Preventing cardiovascular disease in women:

How much physical activity is “good enough”?

Introduction

The term cardiovascular disease is used by medical professionals to refer to both coronary heart disease (CHD) and stroke; both

conditions are usually caused by insufficient blood supply. In most cases, the reduced blood flow results from atherosclerosis, or the

accumulation of fatty plaques in artery walls that causes arteries to narrow and harden. If a blood clot or plaque rupture blocks a

narrowed artery leading to the heart, it can cause a heart attack; if the artery that is blocked instead leads to the brain, it can cause a

stroke. 

Until recently, cardiovascular disease, especially CHD, was widely perceived to be less of a public health problem for women than

for men. Although CHD tends to appear later in women than it does in men (10 years later for total CHD and 20 years later for its

most serious manifestations such as heart attack), CHD nevertheless becomes the leading killer of U.S. men by 45 years of age and

of women by 65 years of age. In fact, once women develop CHD, they have a markedly worse prognosis than men. For example,

38% of women but only 25% of men die within one year after having a first heart attack. Moreover, 64% of women but only 50%

of men who die suddenly from CHD have no prior symptoms of the disease. In recent years, declines in cardiovascular deaths have

also been less pronounced among women than among men (Figure 1).1 Boosting prevention and treatment efforts among women is

necessary to forestall potentially widening gender disparities in cardiovascular outcomes. One potent protective factor that should

be targeted for promotion is physical activity.

Figure 1.

Cardiovascular Disease Mortality Trends for Males and Females

United States: 1979-2001

Reprinted from American Heart Association, Heart Disease and Stroke

Statistics–2004 Update. Dallas, Texas: American Heart Association, 2003.

Copyright © 2003, American Heart Association. Used with permission.

Researchers generally agree that physical activity provides cardiovascular benefits. In

1990, a quantitative review of 27 longitudinal studies in mostly male populations

concluded that physically active individuals have about half the CHD risk of those

who are sedentary, and studies conducted within the last 15 years also indicate that

physically active women are less likely to develop CHD than their inactive

counterparts. However, there is still debate on the amount or “dose”—a function of

duration, frequency, and intensity—of physical activity required for optimal health.

Series 5, No. 4 Dec. 2004

Published quarterly by the

President’s Council on

Physical Fitness and Sports

Washington, D.C.

★

Guest Authors:

Shari S. Bassuk, ScD1

JoAnn E. Manson, MD, DrPH1,2

Division of Preventive Medicine,

Department of Medicine

Brigham and Women’s Hospital

Harvard Medical School

Boston, Massachusetts

Department of Epidemiology

Harvard School of Public Health

Boston, Massachusetts

★

Co-edited by:

Drs. Charles B. Corbin and

Robert P. Pangrazi,

Arizona State University, and

Dr. Deborah Young,

University of Maryland

President’s Council on Physical Fitness and Sports

ResearchDi est
Duration refers to how long one exercises; frequency, how

often. Intensity refers to how “hard” one exercises and is

typically measured in kilocalories (kcal) burned per minute

or in a unit called the metabolic equivalent (MET). One MET

is the amount of energy (oxygen) that the body expends while

sitting quietly, and is taken as a constant of 1 kcal.kg-1.hr-1. A

2-MET activity expends twice the energy of sitting quietly; a

3-MET activity expends three times the energy of sitting

quietly; and so forth. Moderate-intensity activities, such as

brisk walking, are those that burn 3.5 to 7 kcal per minute

(for a 70-kg person) or, equivalently, those that expend 3 to 6

METs. Vigorous activities, such as running, are those that

burn more than 7 kcal per minute or expend more than 6

METs.

Physical activity guidelines

The longstanding belief that physical activity must be

vigorous to be healthful has been overturned in the last

decade by epidemiologic studies indicating otherwise.

Earlier guidelines advocating vigorous exercise for at least

20 minutes three times per week have been supplemented by

a widely publicized 1995 recommendation by the Centers for

Disease Control (CDC) and the American College of Sports

Medicine (ACSM) that adults engage in 30 minutes of

moderate-intensity physical activity on most, preferably all,

days of the week (see Corbin, Le Masurier, and Franks,

PCPFS Research Digest, December 2002, at

www.fitness.gov). This has also been the standard endorsed

by the U.S. Surgeon General since 1996. In 2002, the

influential Institute of Medicine (IOM) concurred that

moderately intense activity is beneficial. However, the IOM

concluded that one half-hour is not sufficient to maintain a

healthy weight nor to achieve maximal health benefits and

therefore recommended a 60-minute standard. The IOM

guideline was issued as part of a report focused on providing

diet and nutrition goals for the American public; the report is

available at http://www.nap.edu/books/0309085373/html/.

Although the IOM has been praised for promoting physical

activity as an essential part of a healthy lifestyle, its

recommendation has also been criticized for failing to

balance the issue of efficacy (the most effective amount of

exercise) with that of feasibility (the amount of exercise

people are actually likely to do), both of which are necessary

to achieve a public health goal. A recent national survey

conducted by the U.S. Department of Health and Human

Services found that 73% of women and 66% of men fail to

meet the 30-minute guideline; and 41% of women and 35%

of men engage in no leisure-time physical activity at all

(Figure 2).2 Setting the standard even higher, to 60 minutes,

may erode the motivation the sedentary public—already

largely unable to fulfill the 30-minute goal—might marshal

to adopt a more active lifestyle. Based both on this fact and

our review of scientific data regarding the salutary effect of

even modest amounts of exercise, we, along with many

researchers and policymakers, believe that the public health

message should continue to be that 30 minutes per day of

moderately intense exercise confers significant and

measurable health benefits. Indeed, physical activity

guidelines issued in 2003 by the American Heart Association

(AHA) and endorsed by the ACSM espouse the 30-minute

goal for the prevention of cardiovascular disease, as do the

AHA’s February 2004 cardiovascular prevention guidelines

specifically targeted to women. In June 2004, the AHA

reiterated the 30-minute guideline in a joint statement with

the American Diabetes Association and the American Cancer

Society regarding strategies for preventing cardiovascular

disease, diabetes, and some types of cancer. The World

Health Organization also included the 30-minute

recommendation in its 2004 global blueprint for fighting

these and other chronic diseases. 

30 minutes of moderate exercise per day lowers

the risk of cardiovascular disease

Findings from epidemiologic studies strongly support the

prescription of 30 minutes per day of moderate-intensity

activity to reduce the risk of CHD. For example, among

nearly 74,000 postmenopausal women aged 50 to 79 years

participating in the Women’s Health Initiative, walking

briskly for at least 2 1/2 hours per week (i.e., a half-hour five

times per week)—or expending an equivalent amount of

energy through more vigorous exercise—was associated with

a 30% reduction in cardiovascular events over 3 years of

follow-up.3 The protective effect of walking was observed in

both white and black women, in middle-aged and older

women, and in lean and overweight women (Figure 3). 

The cardiovascular benefits of walking—the most common

leisure activity among U.S. adults—have also been

demonstrated in other studies of women. In the Nurses’

Health Study, which followed 72,000 healthy middle-aged

female nurses for 8 years, women who walked briskly for 3

hours per week or, alternatively, exercised more vigorously

for 1 1/2 hours per week, had a 30 to 40% lower incidence of

heart attack than did sedentary women.4 In the Women’s

Health Study, a 7-year follow-up of 39,000 healthy middleaged female health professionals, walking at least 1 hour per

week was associated with a 50% reduction in CHD risk in

women reporting no vigorous physical activity.5 Among

1,564 middle-aged University of Pennsylvania alumnae

followed for 30 years, walking 10 or more blocks per day as

compared with walking less than 4 blocks per day was

associated with a one third reduction in cardiovascular

disease incidence.6 Among community-dwelling women and

men aged 65 years and older, walking more than 4 hours per

week, as compared with walking less than 1 hour per week,

 

0

10

20

30

40

50

18-24 25-44 45-64 65-7 4 75+

Age (years)

46.0

31.9

36.0

31.1 31.6

26.7

30.6

20.2 21.9

11.2

*Regular activity = light-to-moderate activity 5 times or more per

 week for 30 minutes each time, or vigorous activity 3 times or more

 per week for 20 minutes or more each time.

 Data from Schoenborn CA, Barnes PM. Leisure-time physical activity

 among adults: United States, 1997-98. Advance data from vital and health

 statistics; no. 325. Hyattsville, MD: National Center for Health Statistics,

 2002.

Figure 2

Percent of U.S. adults engaging in regular

leisure-time physical activity,* by gender and age

Men

Women

2
as well, albeit somewhat less strongly, perhaps due to

generally higher physical activity levels for men as compared

with women. Nevertheless, in the Health Professionals

Follow-up Study, a 12-year follow-up of 44,000 healthy male

health professionals aged 40 to 75 years, a half-hour per day

or more of brisk walking was associated with an 18%

reduction in CHD incidence.8 In the Honolulu Heart

Program, men aged 71 to 93 years who walked 1 1/2 miles

per day experienced half the risk of CHD of those who

walked less than 1/4 mile per day.9 In the Zutphen Elderly

Study, men aged 64 to 84 years who walked or cycled at least

3 times per week for 20 minutes were 31% less likely to die

from CHD over a 10-year follow-up period, compared with

their counterparts who did not meet this activity criterion.10

Studies in men suggest that vigorous exercise is associated

with even greater reductions in the risk of cardiovascular

disease than is moderate-intensity exercise.8,10

Physical activity is also associated with a reduced risk of

stroke, although available data are less extensive than for

CHD outcomes. A quantitative review of 18 longitudinal

studies that included a high proportion of women found that

moderately active and highly active persons were 17% and

25% less likely, respectively, to have a stroke or die of

stroke-related causes than were persons with low activity.11

In the Nurses’ Health Study, women in the highest activity

category experienced only half the risk of ischemic stroke as

the least active respondents.12 Ischemic strokes, which are

caused by blood vessel blockages in the brain, account for

about 80% of strokes in the U.S. Other studies, including the

Physicians’ Health Study, an 11-year follow-up of nearly

22,000 male physicians aged 40 to 84 years, indicate that

physical activity may also be beneficial in preventing

hemorrhagic stroke, a type of stroke that can occur when

blood vessels in the brain burst and saturate surrounding

tissues with blood.13

Physical activity versus cardiorespiratory

fitness

The above studies examined self-reported physical activity

levels in relation to cardiovascular outcomes and thus offer

direct support for public health guidelines on cardiovascular

disease prevention. Such guidelines are framed in terms of

physical activity, a behavior, rather than physical fitness, a

biologic state. However, a high level of cardiorespiratory

fitness, defined as the ability of the body’s circulatory and

respiratory systems to supply energy (oxygen) during

sustained activity, has also been shown to predict lower

cardiovascular death rates in initially healthy women and

men. Cardiorespiratory fitness, also known as exercise

capacity, is commonly measured by treadmill exercise testing

and expressed in METs. In a 20-year follow-up of 2,994

women aged 30 to 80 years in the Lipid Research Clinics

Study, the risk of death from cardiovascular causes and from

all causes decreased by 17% and 11%, respectively, for each

1-MET increase in exercise capacity, after factoring out the

effects of other cardiovascular risk factors.14 In an 8-year

follow-up of 5,721 women aged 35 and older (the St James

Women Take Heart Study), death from all causes declined by

17% for each 1-MET increase in exercise capacity.15

Although regular physical activity boosts physical fitness, the

degree to which being inactive and being unfit represent

distinct risk factors for cardiovascular disease is uncertain.

Indeed, the intensity and amount of exercise an individual

needs to reduce his or her cardiovascular risk likely depends

significantly reduced the risk of hospitalization for

cardiovascular reasons.7

Benefits of walking have been observed in male populations

3

Energy expenditure from walking (MET hr/wk)

0. 0

0. 2

0. 4

0. 6

8

0

2 0 0.1-2.5 2.6-5.0 5.1-10 10+

1.00*

0.85

0.70

0.66

0.55

P for trend <0.001

1.00* 1.00

0.67

0.73

0.65

P for 

trend=0.11

White Women (n=61,574) Black Women (n=5,661)

Race

Age-Adjusted Relative Risk of Cardiovascular Disease

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.00* 1.00* 1.00*

0.89

0.78

0.72 0.72

P for trend <0.001 P for trend <0.001 P for trend=0.004

0.91

0.70

0.49

0.66

0.78

0.49

0.46

0.51

50-59 yr (n=24,803) 60-69 yr (n=32,127) 70-79 yr (n=15,856)

Age

0. 0

0. 2

0. 4

0. 6

0. 8

1. 0

1. 2

P for trend =0.003 P for trend <0.001 P for trend <0.001

1.00*

0.79 0.78

0.59 0.56

1.00*

0.90

0.71

0.64

0.75

1.00*

0.9

5

0.71 0.75

0.67

BMI <25.0 BMI 25.0-29.9 BMI 30.0+ 

(n=30,583) (n=24,590) (n=16,806)

 

*The reference category is the lowest category of energy expenditure 

from walking.

Reproduced from Manson JE et al. N Engl J Med 2002;347:716-25. 

Copyright ©2002, Massachusetts Medical Society. Used with permission.

Body Mass Index

Figure 3

Age-adjusted relative risks of cardiovascular disease according to energy

expenditure from walking (MET hour/week) in subgroups defined by race,

age, and body mass index.
4

on his or her baseline fitness level. This explanation may

account for the above-mentioned gender differences in

epidemiologic findings regarding the level of exercise

intensity necessary for CHD risk reduction. In general,

studies that indicate that moderate-intensity activity is

sufficient to decrease cardiovascular risk have been carried

out in women or older men, who tend to be less fit, whereas

studies that have reported that vigorous activity is required to

reduce such risk have been conducted in young or middleaged men, who tend to be more fit. 

A “good-enough” level of physical activity

In light of the above data, how do we resolve the discrepancy

between the 30-minute physical activity guideline of the

CDC/ASCM, Surgeon General, and AHA and the 1-hour

recommendation of the IOM? The answer is by recognizing

that there is in fact no actual discrepancy, only an apparent

one arising from differences in which aspect of scientific

findings were emphasized by the guideline authors and

subsequently publicized by the media (see Corbin, Le

Masurier, and Franks PCPFS Research Digest, December

2002, at www.fitness.gov). Moderately intense exercise for

one half-hour per day confers significant and measurable

cardiovascular health benefits, as the data on walking show.

It is also true, however, that a dose-response relationship

between physical activity and cardiovascular outcomes exists

such that another half-hour of exercise would, on average, be

expected to confer additional protection against the

development of cardiovascular disease in sedentary societies

such as ours. This fact was clearly acknowledged by the

CDC/ACSM and the Surgeon General, even as they issued

their 30-minute-per-day guideline: “People who already meet

the recommendation are also likely to derive some additional

health and fitness benefits from becoming more physically

active.” By contrast, the IOM, in advocating a higher

exercise dose for the optimization of health, may not have

sufficiently credited the role of more modest physical activity

achievements in lowering disease risk. 

Physical activity and weight control

Whether a person is overweight or obese is often measured

with a statistic known as body mass index (BMI), calculated

by dividing one’s weight in kilograms (kg) by the square of

height in meters (m). Using commonly accepted cut points,

individuals with BMI of 18.5 to 24.9 kg/m2 are classified as

having a healthy weight; those with BMI of 25 to 29.9 kg/m2

are classified as overweight; and those with a BMI of 30

kg/m2 or greater are classified as obese. The primary

rationale given by the IOM for its physical activity

recommendation is that one half-hour of exercise per day has

not been consistently shown to ensure maintenance of a

healthy weight or to foster weight loss in the absence of

curtailing caloric intake. 

Some evidence does suggest that an hour of activity per day

may be necessary to control weight when dietary restraint is

not practiced concurrently. In an IOM-compiled database of

some 400 healthy stable-weight adults whose energy

expenditures had been estimated using a biochemical method

considered to be the gold standard of energy expenditure

measurement, individuals with a BMI between 18.5 and 24.9

kg/m2 expended a daily energy equivalent of at least one hour

of moderate physical activity—or, as the IOM phrased it,

walking at least 4.4 miles per day at the rate of 2 to 4 miles

per hour. (This energy expenditure could also result from

lighter activity over a longer duration or more vigorous

activity over a shorter duration.) Moreover, descriptive

studies of formerly obese individuals suggest that 80 minutes

per day of moderately intense activity or 35 minutes per day

of vigorous activity is required for long-term maintenance of

weight loss. In the National Weight Control Registry, a

sample of 629 women and 155 men who lost an average of

30 kg and maintained a minimum weight loss of 13.6 kg for

5 years, the self-reported median energy expenditure was

approximately 2800 kcal per week, or about 1.5 hours of

brisk walking per day for a 65-kg woman.16

On the other hand, findings from randomized trials of

exercise in overweight, sedentary individuals who were

asked to adhere to their usual eating pattern suggest that

lesser amounts of physical activity can also have a beneficial

effect on weight control. For example, a one-year trial that

randomly assigned 173 postmenopausal women with an

average BMI of 30.5 kg/m2 to 45 minutes of moderateintensity exercise 5 days per week or to a stretching control

group found significant reductions in weight even among

women whose exercise amounts fell short of the prescribed

intervention.17 Women in the intervention group, who

exercised an average of 3 1/2 days for 176 minutes per week,

experienced an average BMI reduction of 0.3 kg/m2, whereas

BMI of the controls increased by 0.3 kg/m2. Moreover,

women who were highly active (exercised more than 195

minutes per week) or moderately active (135 to 195 minutes

per week) each lost more total body fat and abdominal fat

than did women in the control group. Another recent study

using nationally representative data has estimated that a mere

100 kcal per day change in energy balance could prevent

weight gain in the majority of 20- to 40-year-old Americans,

and that modest increases in physical activity, such as

walking an additional 15 minutes per day, or reductions in

food intake, such as consuming a few less bites per meal,

would bring about the desired change.18 These data indicate

that an hour of exercise per day may not be necessary to

derive measurable benefits with respect to weight control. 

Other mechanisms by which physical activity

reduces cardiovascular disease risk

Physical activity reduces cardiovascular risk not only by

promoting weight maintenance or loss but also by processes

that are, at least in part, independent of weight regulation.

Regular exercise lowers blood pressure, reduces the risk of

developing type 2 diabetes, and boosts levels of high-density

lipoprotein (HDL) cholesterol (the “good” cholesterol). For

example, among Nurses’ Health Study participants who did

not engage in vigorous physical activities, walking briskly

for 3 hours per week was predictive of a 26% reduction in

the incidence of type 2 diabetes, after adjusting for the

effects of excess body weight and other variables.19

Blood pressure. Findings from randomized trials indicate

that moderate-intensity exercise is at least as effective as

high-intensity exercise at lowering blood pressure; such

effects occur in persons with normal blood pressure and

those with hypertension (high blood pressure) and are largely

independent of weight change. In a quantitative review of 54

randomized trials that enrolled 2419 participants, exercise

led to an average reduction of 3.9 mm Hg in systolic blood

pressure (the top number in a blood pressure reading) and 2.6

mm Hg in diastolic blood pressure (the bottom number).

Among participants with hypertension, the reduction was

even greater—4.9 and 3.7 mm Hg for systolic and diastolic

pressures, respectively.20 In an analysis of 16 trials (650

participants) that employed walking as the sole activity
intervention, systolic/diastolic blood pressure decreases of

3/2 mm Hg were observed after an average of 25 weeks of

treatment in people with normal blood pressure and in those

with hypertension.21 Both analyses included trials with a

large percentage of female participants and found that the

effectiveness of the exercise intervention did not vary by

gender.

Type 2 diabetes. Type 2 diabetes mellitus, a metabolic

disorder characterized by excess glucose (sugar) in the blood

resulting from defects in insulin action, is a major risk factor

for cardiovascular disease, especially among women.

Whereas men with diabetes are 2 to 3 times more likely to

develop cardiovascular disease than are men without

diabetes, women with diabetes are 3 to 7 times more likely to

do so than are their counterparts without the condition.

Moderate- and high-intensity exercise appear to be equally

effective in improving blood glucose control and insulin

action and lowering diabetes risk. In the Nurses’ Health

Study, brisk walking and more vigorous activity were

associated with comparable reductions in type 2 diabetes

risk, after adjustment for total exercise energy expenditure.19

A 6-year follow-up of 1,728 Pima Indians in Arizona, a

community with one of the world’s highest rates of type 2

diabetes and a high prevalence of obesity, found that

recreational physical activity at levels meeting the 30-minute,

moderate-intensity public health guideline was associated

with a 26% reduction in diabetes risk in women and a 12%

reduction in men, after factoring out the effect of BMI.22

Clinical trials conducted in high-risk populations also

indicate that physical activity lowers the risk of diabetes. For

example, in the Da Qing Impaired Glucose Tolerance and

Diabetes Study, 577 middle-aged Chinese women and men

with impaired glucose tolerance—a condition in which blood

glucose levels are higher than normal but not high enough to

be classified as full-fledged diabetes—were randomized to

one of three treatment groups—diet only, exercise only, or

diet plus exercise—or to a control group.23 Over 6 years, the

three interventions were associated with reductions of 31%,

46%, and 42% in diabetes risk, respectively. Notably,

overweight and lean participants experienced similar

reductions in diabetes risk. The U.S. Diabetes Prevention

Program, a 3-year follow-up of 3,234 women and men aged

25 to 85 years with impaired glucose tolerance and BMI of

24 kg/m2 or more, reported a 58% reduction in diabetes risk

among the intervention group, whose members, on average,

performed moderate-intensity exercise for 30 minutes per

day (most chose walking) and lost 5 to 7% of their body

weight during the trial.24 This study oversampled older

persons, as well as members of racial/ethnic groups that

suffer disproportionately from diabetes (black, Hispanic, and

Asian Americans; Pacific Islanders; and American Indians),

and found that the lifestyle intervention was effective in

reducing diabetes risk in all of these groups. Indeed, among

people aged 60 and older—a group with a diabetes

prevalence of nearly 20%—the intervention was associated

with a 71% reduction in diabetes risk. 

An estimated 75% of people who have diabetes eventually

die from cardiovascular complications. However, several

long-term studies, including the large Nurses’ Health Study,25

suggest that people with diabetes who engage in regular

moderate-intensity physical activity can sharply cut their

odds of developing, or dying from, cardiovascular disease.

Among 2,449 adults with diabetes in the National Health

Interview Survey, walking 2 or more hours per week, as

compared with not walking, was predictive of a 41% reduction

in the cardiovascular death rate during 8 years of follow-up.26

A large ongoing trial, the Look AHEAD (Action for Health

in Diabetes) study funded by the National Institute of

Diabetes and Digestive and Kidney Diseases, should provide

valuable randomized data about the long-term (11 1/2 years)

effects of regular exercise and decreased caloric intake on the

risk of developing cardiovascular disease in obese persons

with diabetes.27

Lipid profile. In contrast to the findings for blood pressure

and glucose control, stronger dose-response relationships

between exercise intensity and blood lipids—specifically,

HDL cholesterol and triglycerides—have been reported in

observational studies. Nevertheless, a recent 8-month trial

that assigned overweight middle-aged women and men to

various exercise regimens or to a nonexercising control

group found that, although improvements in lipid profile

were far more striking among the “high-amount/highintensity” exercise group than among either the “lowamount/high-intensity” and “low-amount/moderateintensity” groups, a comparison of the latter two groups

showed that they experienced similar improvements in lipid

profile to each other.28 On the basis of these results, the

investigators conclude that lipid profile is related more

strongly to the amount, rather than the intensity, of exercise.

Favorable effects of brisk walking (three 50-minute sessions

per week) on blood lipids were also found in a 10-week

randomized trial of women aged 70 to 87 years.29 In these

trials, the beneficial effects of exercise occurred in the

absence of concurrent dietary change.

Novel risk factors. Accumulating data indicate that exercise

favorably influences not only the established risk factors for

cardiovascular disease described above but also a variety of

newly recognized risk factors. Although comparable studies

in women are lacking, studies in healthy men suggest that

both moderate-intensity and vigorous exercise alter the

body’s production of various factors that work in concert to

regulate blood clotting. That is, exercise helps maintain the

proper balance between substances that stimulate clot

formation—including proteins called coagulation factors and

viscous (sticky) blood cells called platelets—and those that

counteract this effect by promoting blood thinning. Trials of

men with hypertension, diabetes, or preexisting heart disease

suggest that exercise can also improve the functioning of the

cells that line the blood vessel walls. Collectively termed the

endothelium, these cells have been shown to respond to

regular exercise by producing more nitric oxide, a substance

that relaxes blood vessels, thereby increasing the ability of the

vessels to dilate in response to blood flow. Improved regulation

of blood coagulation and viscosity and improved endothelial

function are believed to lessen the risk of unhealthy blood

clots and thus of heart attack and ischemic stroke.

The protective effect of physical activity may also be a result

of its influence on inflammation. In large observational

studies of women and men, exercise has been linked to lower

levels of various inflammatory markers in the blood,

including C-reactive protein and interleukin-6. Inflammation

is thought to destabilize fatty atherosclerotic plaques in heart

and brain arteries. By reducing inflammation, exercise may

promote the stability of these plaques, thus reducing the odds

that they will rupture and precipitate a heart attack or stroke.

Taken in the aggregate, these findings suggest that the

cardiovascular benefits derived from physical activity are not

solely a function of weight regulation. Indeed, in the largescale Nurses’ Health Study, walking was associated with a

5
Study, which examined changes in physical activity over 14

years among 5,934 men aged 40 to 59 years at baseline,

found that men who took up even light activity in later life

experienced a 34% reduction in cardiovascular death over the

subsequent 4 years as compared with men who remained

inactive.34 Similarly, the Study of Osteoporotic Fractures,

which assessed physical activity changes over 6 years among

7,553 women aged 65 years and older at baseline, reported

that women who increased their physical activity level were

36% less likely to die of cardiovascular causes during the

subsequent 7 years than were women who stayed sedentary.35

Nevertheless, both studies also indicate that exercise must be

current and habitual to confer cardiovascular protection; men

and women who became inactive in later life had a similar

risk of cardiovascular death to those who had remained

inactive over the course of follow-up. 

Effect of race/ethnicity. There are sparse data on the

relationship between physical activity and cardiovascular

disease in nonwhite populations. However, results from the

Women’s Health Initiative, one of the few studies to include

a sufficient number of black participants to permit an

examination of the association between physical activity and

CHD in this group, show that black women derive

comparable cardiovascular benefits from exercise as do white

women.3 In both racial groups, 30 minutes per day of brisk

walking, or more vigorous exercise, was associated with an

approximate 30% reduction in CHD risk. Such evidence

regarding the applicability of national activity guidelines to

black Americans is important because of the high prevalence

of physical inactivity, obesity, hypertension, type 2 diabetes,

and cardiovascular disease in this group. In a recent national

survey, 55% of black women and 44% of black men reported

no leisure-time physical activity, as compared with 36% of

white women and 33% of white men.1 An estimated 40% of

black women and 41% of black men have cardiovascular

disease, whereas the corresponding figures for whites are

24% and 30%.1 Although the reasons for racial disparities in

health are not completely understood, with differing physical

activity patterns being only one piece of a complex puzzle,

targeted initiatives to increase physical activity among U.S.

blacks may help ameliorate their disadvantaged

cardiovascular status vis-à-vis U.S. whites. 

Strength training. Most epidemiologic studies of physical

activity have focused on aerobic exercise such as walking.

However, resistance exercise, also known as strength

training, may also reduce CHD risk. In the Health

Professionals Follow-up Study, men who trained with

weights for at least 30 minutes per week were 23% less

likely to develop CHD during 8 years of follow-up than were

men who did not train with weights.8 Resistance exercise is

known to improve blood glucose control and may also

improve blood lipid profile and lower blood pressure.

Resistance exercise also confers noncardiovascular benefits,

most notably the preservation of bone and muscle, which

may be particularly important for women, who are at higher

risk for bone thinning and fractures than are men. It is

therefore of great concern that only 16% of U.S. women

aged 45 to 64 years and less than 10% of women aged 65

years and older report ever engaging in strengthening

activities.2

Prolonged sitting and other sedentary behaviors. Recent

studies demonstrate the health benefits not only of obtaining

adequate aerobic and resistance exercise but also avoiding

sedentary behaviors such as prolonged sitting. Highlighting

6

reduced incidence of cardiovascular disease even after

factoring out the effects of changes in participants’ BMI over

time. Thus, focusing on excess weight—as powerful a

cardiovascular disease risk factor as it is—as the primary

guidepost yields an incomplete picture when assessing the

impact of physical activity on cardiovascular health.

Other efficacy and feasibility issues

Calorie control. Indeed, if obesity rather than cardiovascular

disease is the outcome of interest, then it should be kept in

mind that energy output from physical activity, is only one

half of the energy balance equation. Energy input is the other

half, and this topic, rather than physical activity, is the main

focus of the aforementioned IOM report. The most effective

weight-loss programs combine calorie control with physical

activity. Given the trend of ever-increasing portion sizes,

reinforcing the importance of dietary moderation is crucial to

halt the pandemic of obesity, the prevalence of which jumped

from 14.5% in 1980 to 30.4% in 2002.30 Otherwise,

recommended exercise doses will creep inexorably upward

in an attempt to keep waistlines from expanding. It is

plausible that one half-hour of exercise per day, in

combination with modest-to-moderate dietary restraint, will

confer cardiovascular benefits of equal magnitude to those

conferred by one hour of exercise per day in the absence of

caloric restriction. The former prescription may be more

feasible to achieve than the latter in our time- but not fooddeprived society. This issue is particularly salient for U.S.

women, as national data indicate that their average caloric

intakes increased by a much larger percentage than did those

of U.S. men during the past 3 decades. From 1971 to 2000,

the daily caloric intake of the typical woman rose 22%, from

1542 to 1877 kcal, while the typical man increased his intake

by 7%, from 2450 to 2618 kcal.31 Although comparable data

on national trends in physical activity during this period are

lacking, activity levels among U.S. women and men

remained relatively stable during the 1990s,32 suggesting that

diet is at least as important as exercise in controlling weight. 

Short vs. long bouts of exercise. Because exercise must be

current and habitual to confer cardiovascular protection, the

ability to incorporate it into one’s daily schedule is crucial.

Especially welcome news to time-pressured individuals

should be findings from studies showing that short durations

(as short as 10 minutes) of exercise favorably affect

cardiovascular risk factors. To date, only one longitudinal

study has examined the relationship between short bouts of

exercise and the risk of cardiovascular disease itself. Among

7,337 middle-aged and elderly men followed for 5 years in

the Harvard Alumni Health Study, exercising in 15-, 30-, or

45-minute bouts all offered similar protection against

cardiovascular disease, given an equivalent total exercise

energy expenditure per week.33 To date, no parallel studies

have been conducted in female populations. However, it is

not unreasonable to speculate that comparable findings

would be observed among similarly aged women. From a

public health perspective, this knowledge may help busy

individuals to consider exercise a manageable part of their

daily routine rather than a “production number” to be

undertaken only on rare occasions. 

Effect of age. For aging populations, additional motivation to

exercise is provided by data that strongly support the adage

“it’s never too late.” Several long-term studies suggest that

adopting a physically active lifestyle even in late adulthood

may lower cardiovascular risk. The British Regional Heart
7

this distinction in future public health messages would seem

to be warranted, given that the typical U.S. adult spends 4 to

5 hours per day watching television,36 and many individuals

sit for an additional 8 or more hours while at work.

Prolonged sitting predicts an increased risk for diabetes and

cardiovascular disease, even after accounting for time spent

in recreational exercise. Among women in the Nurses’ Health

Study, each 2-hour-per-day increment in television watching

was associated with a 14% increase in the risk of diabetes.37

Among participants in the Women’s Health Initiative, those

who spent 16 or more hours per day sitting were 68% more

likely to develop cardiovascular disease than those who spent

less than 4 hours per day sitting.3

Clinician counseling and other interventions. Because of a

lack of research, it is not known whether brief counseling by

primary care physicians during routine office visits is

effective in producing sustained physical activity increases

among their patients. Nonetheless, it is sobering to note that,

despite the fact that 2 of 3 U.S. adults do not exercise enough

to meet the 30-minute-per-day guideline, only 1 in 3 adults

who saw a physician in the prior year were counseled about

physical activity at their last visit.38 Data from randomized

clinical trials suggest that so-called “lifestyle activity”

interventions, which encourage sedentary individuals to

incorporate short bouts of physical activity into their daily

life (e.g., taking short walks during lunch or coffee breaks;

doing yard work or gardening; and using the stairs instead of

the elevator), can be more effective than traditional exercise

programs (e.g., structured workout sessions at the gym) in

boosting activity levels and improving physical fitness and

cardiovascular risk profiles.39 Urgently needed are additional

studies to identify specific characteristics of interventions—

both interventions implemented at the individual level (e.g.,

one-on-one counseling of patients by healthcare providers)

and those implemented at the community level (e.g.,

increasing the availability of walking trails, bike paths, and

other recreation-friendly spaces in urban and suburban

environments)—that can bring about lasting improvements

in exercise behaviors.

Safety issues

In addition to issues of efficacy and feasibility, initiatives to

boost physical activity must adequately address safety

concerns. Exercise is not an unqualified boon with respect to

either cardiovascular or muscle and bone health, especially

among persons who already have heart disease or diabetes or

who are not accustomed to exercising. Risks of overexercise,

especially vigorous exercise, include sudden cardiac death,

fall-related injuries, other muscle and bone injuries, and, for

women, menstrual and reproductive problems. While

physical inactivity and overeating exact a far greater toll on

the health of U.S. adults than do excessive exercise and

overzealous dieting, these factors must not be ignored by

healthcare providers and public health professionals.

Conclusion

To lead to tangible improvements in health, the findings of

scientific research must be skillfully translated into

healthcare practice and public health policy. Such translation

requires the balancing of efficacy, feasibility, and safety

issues. The challenge to healthcare providers and

policymakers is determining how best to promote appropriate

levels of regular physical activity to their patients and to the

general public, respectively. We believe that the public health

message should remain “30 minutes per day is good, and

more is better, to a reasonable extent.” As the eminent British

epidemiologist Geoffrey Rose stated in his classic text The

Strategy of Preventive Medicine, the overall burden of

disease in a given population is likely to undergo a more

dramatic reduction when a large segment of that population

adopts modest improvements in health behaviors than when

a modest segment of that population adopts large

improvements. 

Note: References are included in the electronic version found at www.fitness.gov.
8

Please Post

President’s Council on Physical Fitness & Sports

200 Independence Avenue, S.W., Washington, DC 20201

(202) 690-9000 • FAX (202) 690-5211

“Epidemiologic studies suggest that

30 minutes per day of brisk walking

can reduce the occurrence of

cardiovascular disease in women

and men. In a sedentary society

such as ours, public health initiatives

that promote moderate increases in

physical activity may represent the

optimal balance between efficacy,

feasibility, and safety to achieve the

desired cardiovascular benefit.”

Shari S. Bassuk, ScD1

JoAnn E. Manson, MD, DrPH1,2

1Division of Preventive Medicine,

Department of Medicine

Brigham and Women’s Hospital

Harvard Medical School

Boston, Massachusetts

2Department of Epidemiology

Harvard School of Public Health

Boston, Massachusetts
9

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