NCHS Data Brief ¡ No. 6 ¡ May 2008

Folate is an essential vitamin for good health. Women of childbearing age are 

among the population subgroups that have been shown previously to have 

low blood folate levels (1,2). Low blood folate levels are associated with 

an increased risk of neural tube birth defects. Beginning in 1998, the Food 

and Drug Administration (FDA) required the addition of folic acid (a form 

of folate) to all enriched breads, cereals, flours, corn meal, pasta products, 

rice, and other cereal grain products sold in the United States (3). Blood 

folate data from the National Health and Nutrition Examination Surveys 

(NHANES) have documented improvements in the folate status of the U.S. 

population after folate fortification was implemented (4). Red blood cell 

(RBC) folate measures long-term folate intake and low levels are associated 

with adverse health effects. Serum folate reflects recent folate intake and low 

levels are an early indicator of inadequate folate status. Pre- and postfortification blood folate levels of the U.S. population 4 years of age and older and 

prevalence of low blood folate among women of childbearing age (15–45 

years) are reported. 

Keywords: folic acid fortification, prevalence, red blood cell folate, serum 

folate, survey, trends, National Health and Nutrition Examination Surveys

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

National Center for Health Statistics

Key findings

Data from the National 

Health and Nutrition

Examination Surveys

• Very large increases in 

blood folate levels of the U.S. 

population occurred between 

1988–1994 and 1999–2000. 

Small fluctuations in blood 

folate levels occurred over the 

time period 1999–2006. 

• The median red blood cell 

(RBC) folate level of the U.S. 

population 4 years of age 

and older was 266 ng/mL in 

2005–2006. 

• The median serum folate 

level of the U.S. population 

4 years of age and older was 

12.2 ng/mL in 2005–2006.

• In 2005–2006, the prevalence of low RBC folate (less 

than 140 ng/mL) among U.S. 

women of childbearing age 

(15–45 years) was 4.5%. 

• In 2005–2006, the prevalence of low serum folate (less 

than 3 ng/mL) among U.S. 

women of childbearing age 

was 0.3%. 

Blood Folate Levels: The Latest NHANES Results

Margaret A. McDowell, M.P.H., R.D.; David A. Lacher, M.D.; Christine M. Pfeiffer, Ph.D.; Joseph Mulinare, 

M.D., M.S.P.H.; Mary Frances Picciano, Ph.D.; Jeanne I. Rader, Ph.D.; Elizabeth A. Yetley, Ph.D.; Jocelyn 

Kennedy-Stephenson, M.S.; and Clifford L. Johnson, M.S.P.H. 

1988–

1994

1999–

2000

2001–

2002

2003–

2004

2005–

2006

Figure 1. Median RBC folate levels (ng/mL) of the U.S. population, 1988–2006 

0

100

150

50

200

250

300

Year

Median RBC folate

(ng/mL)

Persons 4 years of age and older

Females 15–45 years of age

NOTES: Statistically significant difference between 1988–1994 and 1999–2000 for both groups. Statistically 

significant difference between 2001–2002 and 2003–2004 for both groups. Statistically significant 

difference between 2003–2004 and 2005–2006 for both groups. RBC is red blood cell.

SOURCE: CDC/NCHS, National Health and Nutrition Examination Surveys.
■ 2 ■

NCHS Data Brief ¡ No. 6 ¡ May 2008

Have levels of RBC folate, a measure of long-term body stores changed 

since NHANES III (1988–1994)?

Median RBC folate levels increased between 1988 and 1994 (prefortification) and 1999 and 2000 

(postfortification) followed by small fluctuations between 1999–2000 and 2005–2006.

Median RBC folate levels of persons 4 years of age and older increased nearly 60%, from 174 ng/

mL to 276 ng/mL between 1988–1994 and 1999–2000. The NHANES 2005–2006 value is 266 

ng/mL.

Median RBC folate levels of women of childbearing age increased 65%, from 160 ng/mL to 264 

ng/mL between 1988–1994 and 1999–2000. The NHANES 2005–2006 value is 257 ng/mL. 

Has the prevalence of low RBC folate (less than 140 ng/mL) improved since 

NHANES III (1988–1994)? 

The prevalence of low RBC folate in the U.S. population 4 years of age and older declined from 

30.4% in 1988–1994 to 2.8% in 1999–2000 and rates have remained low since that time.

Low RBC folate is of particular concern for women of childbearing age. The prevalence of low 

RBC folate among U.S. women of childbearing age declined from 37.6% in 1988–1994 to 5.1% 

in 1999–2000. The 2005–2006 value was 4.5%. 

The prevalence of low RBC folate was consistently higher among non-Hispanic black women 

compared with non-Hispanic white and Mexican-American women. Significant improvements 

have been made in the RBC folate status of all race and ethnicity groups. Among non-Hispanic 

1988–1994 1999–2000 2001–2002 2003–2004 2005–2006

Year

Percent 1

Significantly different from non-Hispanic white persons and Mexican-American persons.

2

Significantly different from 2003–2004.

NOTES: 1988–1994 rates significantly different from those of the 1999–2006 survey periods. RBC is red blood cell.

SOURCE: CDC/NCHS, National Health and Nutrition Examination Surveys. 

0

10

20

30

40

50

60

70

Figure 2. Prevalence of RBC folate less than 140 ng/mL by racial and ethnic group: Females 15–45 years 

of age, United States, 1988–2006

37.6

5.1 4.0 5.8 4.5

34.5

4.5 2.7 3.6 3.7

1

59.6

1

12.1 1

13.9 1

16.0

1, 29.4

38.7

1.6 2.8 4.9 2.7

Total Non-Hispanic white Non-Hispanic black Mexican American
NCHS Data Brief ¡ No. 6 ¡ May 2008

■ 3 ■

black women, the prevalence of low RBC folate declined from 59.6% in 1988–1994 to 12.1% in 

1999–2000. During the same time period, the prevalence of low RBC folate declined from 34.5% 

to 4.5% among non-Hispanic white women and from 38.7% to 1.6% among Mexican-American 

women.

In 2005–2006, the prevalence of low RBC folate was 9.4% for non-Hispanic black, 3.7% for nonHispanic white, and 2.7% for Mexican-American women. 

Did NHANES 2005–2006 RBC folate levels differ by sex and age? 

Median RBC folate levels varied by sex and age. 

RBC folate levels were lowest among adolescents 12–19 years of age and highest among adults 

60 years of age and older.

Females 60 years of age and older had higher median RBC folate levels (347 ng/mL) compared 

with males 60 years of age and older (304 ng/mL). 

Were there race and ethnicity differences in median RBC folate levels of 

women of childbearing age in 2005–2006? 

Median RBC folate levels of women of childbearing age varied by race and ethnicity.

The median RBC folate level of non-Hispanic black women (210 ng/mL) was significantly lower 

compared with non-Hispanic white and Mexican-American women, whereas the median levels of 

non-Hispanic white (272 ng/mL) and Mexican-American (252 ng/mL) women were similar. 

Figure 3. Median RBC folate levels by sex and age: United States, 2005–2006

1

Significantly different from persons 4–11, 20–59, and 60 years of age and older.

2

Significantly different from persons 4–11, 12–19, and 20–59 years.

3

Significantly different from males 60 years of age and older.

NOTE: RBC is red blood cell.

SOURCE: CDC/NCHS, National Health and Nutrition Examination Surveys. 

0

50

100

150

200

250

300

350

400

Total sample Male Female

4–11 years 12–19 years 20–59 years 60 years of age and older

Median RBC folate (ng/mL)

266

1

234

261

2

332

268 254 1

233

2

304

265 1

237

271

2,3347
■ 4 ■

NCHS Data Brief ¡ No. 6 ¡ May 2008

Have median serum folate levels, a measure of recent folate intake, 

changed since NHANES III (1988–1994)?

Median serum folate levels nearly tripled for the U.S. population 4 years of age and older from 

5.5 ng/mL in 1988–1994 (prefortification) to 14.2 ng/mL in 1999–2000 (postfortification). 

After a modest decline in median serum folate levels from 1999–2000 through 2003–2004, the 

2005–2006 estimate of 12.2 ng/mL shows no change since the previous 2-year period.

Median serum folate levels of women of childbearing age (15–45 years) increased from 4.8 ng/

mL in 1988–1994 to 13.0 ng/mL in 1999–2000. The NHANES 2005–2006 value is 11.4 ng/mL. 

Has the prevalence of low serum folate (less than 3 ng/mL) improved since 

1988–1994?

The prevalence of low serum folate in the U.S. population 4 years of age and older declined from 

15.5% in 1988–1994 to 0.5% in 1999–2000 and rates have remained below 1% since that time.

The prevalence of low serum folate among women of childbearing age declined from 20.6% in 

1988–1994 to 0.8% in 1999–2000. The prevalence of low serum folate has remained low and 

stable among women of childbearing age between 1999–2000 and 2005–2006. 

There were no race and ethnicity differences in the prevalence of low serum folate among women 

of childbearing age in 2005–2006. The prevalence of low serum folate was 0.3% overall and the 

rates were 0.4% for Mexican-American women, 0.0% for non-Hispanic black women, and 0.4% 

for non-Hispanic white women. 

NOTE: Statistically significant differences between 1988–1994 and 1999–2000 and between 1999–2000 and 

2001–2002 for both groups. Statistically significant difference between 2001–2002 and 2003–2004 for persons 4 

years of age and older.

SOURCE: CDC/NCHS, National Health and Nutrition Examination Surveys.

Figure 4. Median serum folate levels (ng/mL) of the U.S. population, 1988–2006 Median serum folate (ng/mL)

0

4

2

8

6

12

14

10

16

Persons 4 years of

age and older

Females 15–45 years of age 

1988–

1994

1999–

2000

2001–

2002

2003–

2004

2005–

2006

Year
NCHS Data Brief ¡ No. 6 ¡ May 2008

■ 5 ■

Did median serum folate levels differ by sex and age in 2005–2006? 

Serum folate levels were highest in young children and older adults; median serum folate was 

significantly higher in children 4–11 years of age and adults 60 years of age and older compared 

with adolescents 12–19 years of age and adults 20–59 years of age. 

Females 60 years of age and older had the highest median serum folate level (17.1 ng/mL) and 

their serum folate level was significantly higher compared with their male counterparts (14.1 ng/

mL). 

Did median serum folate levels of women of childbearing age (15–45 years) 

vary by race and ethnicity group in 2005–2006? 

Non-Hispanic white women had significantly higher median serum folate (11.8 ng/mL) compared 

with non-Hispanic black (9.8 ng/mL) and Mexican-American women (10.4 ng/mL).

Summary

The NHANES data demonstrate that measures of folate status that reflect both short-term and 

long-term folate intake have improved. The median serum and RBC folate levels of the U.S. 

population 4 years of age and older and of women of childbearing age have increased significantly over the time period from 1988 to 2006. The large increases in blood folate levels that occurred 

between 1988–1994 and 1999–2000 were followed by small fluctuations from 1999 to 2006. 

In addition to the overall trends in blood folate, the most recent NHANES data also showed that 

the prevalence of low blood folate has improved among women of childbearing age. The prevalence of low serum folate among women of childbearing age was very low in all racial and ethnic 

groups and significant reductions in the prevalence of low RBC folate have also occurred in all 

Figure 5. Median serum folate levels by sex and age: United States, 2005–2006

0

2

4

6

8

10

12

14

16

18

Total sample Male Female

4–11 years 12–19 years 20–59 years 60 years of age and older

Median serum folate (ng/mL) 1

Significantly different from persons 4–11 and 60 years of age and older.

2

Significantly different from males 60 years of age and older.

SOURCE: CDC/NCHS, National Health and Nutrition Examination Surveys. 

16.4

1

11.6 1

11.2

15.8 16.1

1

10.5

1

11.6

14.1

16.6

1

11.6 1

11.9

2

17.1
■ 6 ■

NCHS Data Brief ¡ No. 6 ¡ May 2008

racial and ethnic subgroups. Government agencies, health care organizations, and health care 

providers are continuing to work together to educate consumers, particularly minority women of 

childbearing age, to consume adequate amounts of folate. 

Definitions

Folate: a water-soluble B vitamin that is found in many foods.

Folic acid: Folic acid is the synthetic form of folate that is found in dietary supplements and 

added to enriched flour and grain products such as breads, pasta, rice, and cereals. 

Median value: The 50th percentile value of the distribution. One-half of the sample (or population) is above the median value and one-half is below the value. 

Neural tube defect: A group of birth defects that are caused by incomplete development of the 

brain, spinal cord, or their protective coverings. Spina bifida is one of the most common types of 

neural tube defects. 

Data source and methods

The National Health and Nutrition Examination Survey (NHANES) data (5) were used for all 

of the analyses presented in this data brief. NHANES is conducted by the Centers for Disease 

Control and Prevention’s (CDC), National Center for Health Statistics, to monitor the health and 

nutritional status of the U.S. population. The annual NHANES samples are composed of the 

civilian, noninstitutionalized U.S. household population. The annual samples are selected using 

a complex, multistage sampling method that includes the selection of primary sampling units 

(counties), household segments within the counties, and sample persons from selected households. Prior to 1999, NHANES data were collected periodically. NHANES became a continuous 

annual survey in 1999. 

Every year approximately 5,000 infants, children, and adults from the United States are selected 

to participate in NHANES. The NHANES sample design includes oversampling in order to 

produce reliable estimates of health and nutritional measures for population subgroups. In 

1999–2006, the oversampled groups included black and Mexican-American persons, persons with 

low income, adolescents 12–19 years of age, and adults 60 years of age and older. 

Survey participants are asked to complete the household interview and health examination components of the survey. The laboratory component of the health examination includes an extensive 

array of laboratory tests that are performed on blood, urine, and other types of specimens. CDC’s 

National Center for Environmental Health Laboratory in Atlanta, Ga., performed the serum and 

RBC folate analyses for NHANES III and NHANES 1999–2006. The folate analysis methodology and quality assurance provisions are described in the NHANES Laboratory Procedures 

Manuals for each of the 2-year survey cycles (6–9). An earlier report examined U.S. blood folate 

trends and methodological considerations for their interpretation (4). 
NCHS Data Brief ¡ No. 6 ¡ May 2008

■ 7 ■

The NHANES examination sample weights were used for all of the data analyses reported. The 

survey sample weights account for the differential probabilities of selection, nonresponse, and 

noncoverage. The standard errors of the percentages were estimated using Taylor series linearization, a method that incorporates the sample weights and sample design (10). Differences between 

groups were evaluated using a univariate t-statistic. Trend tests were performed to evaluate 

changes in blood folate levels over time. Trends were examined using log-transformed data because the blood folate distributions were skewed. All significance tests were two-sided using p < 

0.05 as the level of statistical significance. All data analyses were performed using the statistical 

packages SAS version 9.1 (SAS Institute, Cary, N.C.) and SUDAAN version 9.0 (RTI, Research 

Triangle Park, N.C.). 

About the authors

Margaret A. McDowell, David A. Lacher, and Clifford L. Johnson are with the Centers for Disease Control and Prevention’s (CDC) National Center for Health Statistics, Division of Health 

and Nutrition Examination Surveys; Christine M. Pfeiffer is with CDC’s National Center for 

Environmental Health, Division of Laboratory Sciences; Joseph Mulinare is with CDC’s National Center for Birth Defects and Developmental Disabilities, Division of Birth Defects and 

Developmental Disabilities; Mary Frances Picciano and Elizabeth A. Yetley are with the National 

Institutes of Health, Office of Dietary Supplements; Jeanne I. Rader is with the Food and Drug 

Administration, Division of Bioanalytical Chemistry, Center for Food Safety and Applied Nutrition; and Jocelyn Kennedy-Stephenson is with the Northrop Grumman Corporation under contract to CDC’s National Center for Health Statistics. 

References

1. Senti FR, Pich SM. Analysis of folate data from the second National Health and Nutrition 

Examination Survey (NHANES II). J Nutr 115:1398–402. 1985.

2. Wright JD, Bialostosky K, Gunter EW, et al. Blood folate and vitamin B12: United States, 

1988–1994. National Center for Health Statistics. Vital Health Stat 11 (243):1–78. 1998.

3. Food and Drug Administration. Food standards: Amendment of standards of identity for enriched grain products to require addition of folic acid. Final Rule. Federal Register 61(44):8781–

97. 1996.

4. Pfeiffer CM, Johnson CL, Jain RB, Yetley EA, Picciano MF, Rader JI, et al. Trends in 

blood folate and vitamin B-12 concentrations in the United States, 1988–2004. Am J Clin Nutr. 

86(3):718–27. 2007.

5. Centers for Disease Control and Prevention, National Center for Health Statistics. Datasets and 

Related Documentation. Available from: http://www.cdc.gov/nchs/about/major/nhanes/datalink.

htm [Accessed January 29, 2008.]
6. Centers for Disease Control and Prevention, National Center for Health 

Statistics. Laboratory Manuals and Procedures for NHANES 1999–2000. 

Available from: http://www.cdc.gov/nchs/about/major/nhanes/lab99_00.htm

[Accessed January 29, 2008]. 

7. Centers for Disease Control and Prevention, National Center for Health 

Statistics. Laboratory Manuals and Procedures for NHANES 2001–2002. 

Available from: http://www.cdc.gov/nchs/about/major/nhanes/nhanes2001–

2002/lab01_02.htm [Accessed January 29, 2008]. 

8. Centers for Disease Control and Prevention, National Center for Health 

Statistics. Laboratory Manuals and Procedures for NHANES 2003–2004. 

Available from: http://www.cdc.gov/nchs/about/major/nhanes/nhanes2003–

2004/lab03_04.htm [Accessed January 29, 2008]. 

9. Centers for Disease Control and Prevention, National Center for Health 

Statistics. Laboratory Manuals and Procedures for NHANES 2005–2006. 

Available from: http://www.cdc.gov/nchs/about/major/nhanes/nhanes2005–

2006/lab05_06.htm [Accessed January 29, 2008]. 

10. National Center for Health Statistics. The National Health and Nutrition Examination Surveys (NHANES) Analytic and Reporting Guidelines. 

Updated September 2006. Available from: http://www.cdc.gov/nchs/about/

major/nhanes/nhanes2003–2004/analytical_guidelines.htm [Accessed January 

29, 2008]. 

U.S. DEPARTMENT OF

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National Center for Health Statistics

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NCHS Data Brief ¡ No. 6 ¡ May 2008

ISSN 1941-4927 (Print ed.)

ISSN 1941-4935 (Online ed.)

CS118968

T31372 (05/08)

DHHS Publication No. (PHS) 2008–1209

Suggested citation

McDowell MA, Lacher DA, Pfeiffer CM, 

Mulinare J, Picciano MF, Rader JI, et al. 

Blood folate levels: The latest NHANES 

results. NCHS data briefs, no 6. Hyattsville, 

MD: National Center for Health Statistics. 

2008.

Copyright information

All material appearing in this report is in the 

public domain and may be reproduced or copied without permission; citation as to source, 

however, is appreciated.

National Center for Health 

Statistics

Director

Edward J. Sondik, Ph.D.

Acting Co-Deputy Directors

Jennifer H. Madans, Ph.D.

Michael H. Sadagursky