Yonago Acta medica 2000;43:103–108

Longitudinal Measurements of Bone Density in Adolescent Girls andIntervention in Diet
Keiko Minamimae, Takako Maeda and Tsunakiyo Kasagi
Department of Women’s and Children’s Family Nursing, Faculty of Medicine, Tottori University, Yonago 683-0826 Japan
Ca intake raises bone mineral density (BMD) in adolescence. The present study aimed
at improving BMD in adolescent girls by increasing Ca intake from foods, and developing
a supportive method for keeping this eating habit. In July of 1997 and 1998, BMD of
the left os calcis was measured by ultrasound bone densitometry in 55 college girls
respectively in the 1st and 2nd grades by calculating levels of stiffness which served as
the index for BMD. We told them the analyzed results both times, giving instruction inlife-style for preventing osteoporosis in 1997 and explanation about Ca-rich foods in
1998. After the measurement in 1998, we selected 11 girls with low BMD for the followingintervention in diet (intervention group): i) kind and amount of Ca-rich foods weredaily recorded for 4 weeks; ii) difference between the calculated intake and necessarylevel was told; and iii) subjects were continually encouraged to take daily necessarylevel from foods. Then, BMD of the intervention group was measured 12 weeks after.
Further, in 1999, we measured BMD for the intervention group and 10 selected students
with normal BMD in the 2nd grade (non-intervention group). Mean stiffness was
significantly lower (P < 0.01) in the 2nd grade than in the 1st. In the 2nd grade, theintervention group showed a significantly higher mean 12 weeks after than in July. In
the 3rd grade, the decrease in stiffness was stopped in both groups. The longitudinalmeasurements of BMD over a 2-year period made adolescent girls recognize thedecreasing tendency of BMD. We conclude that adolescent girls can maintain BMD byutilizing their knowledge of preventing osteoporosis and by taking ample Ca from foods.
Key words: adolescent girl; bone density; dietary guidance; longitudinal measurement

Bone mineral density (BMD) in women rapidly
decreases after menopause, and the risk of having osteoporosis or bone fracture becomes higher. To prevent these diseases, it is important toincrease the maximum BMD in adolescenceand to maintain a healthy level (Hirota and
Hirota, 1995). There are many factors affecting
BMD; particularly, what is most important iseating habits (Irie et al., 1996; Yoshida et al.,1997). These days, however, young females are
inclined to miss meals in order to lose weight,
and therefore imbalance in diet is often produced in the population (Maruyama et al.,1993). In 1997, after passing out a booklet, we
lectured female students on critical BMD at

Tottori University College of Medical Care Technology; 6 weeks after, their Ca intake increased
and stiffness rose significantly (Maeda andKitagawa, 1997). However, their Ca intake decreased 12 weeks after to the same level as before our guidance. To get them to retain good
health-keeping behavior firmly on a daily basis
was a problem which had to be solved in the
study.
To improve adolescent female BMD and tosustain the normal level, we carried out longitudinal measurements of BMD in adolescent
girls, intervened in their eating habits and did afollow-up to investigate the effects over a 2year period.

Abbreviations: BMD, bone mineral density; BUA, broadband ultrasound attenuation; SOS, speed of sound103

K. Minamimae et al.

July 1997

July 1998

1st [55]

2nd [55]

1st
guidance

2nd
guidance

BMD measurement

July 1999

Extra

3rd

12 weeks

Intervened
group [11]Girls with low BMD [19]4-week intervention to11 girls
Non-intervened
group [10]Girls with normal BMD [36]Fig. 1. Schema of study and subjects. The extra measurement of BMD 12 weeks after the 2nd measurement
for the intervention group followed our 4-week intervention into the group.

Subjects and Methods

First-grade BMD measurement and 1st
guidance
To measure BMD, we recruited volunteers outof the 80 female students in the 1st grade at
Tottori University College of Medical Care
Technology. We measured BMD of the left os
calcis by the Achilles ultrasound bone densitometer (A-1000 PLUS, Lunar Corp., Madison,
WI) by calculating levels of stiffness from the
SOS and BUA, which serve as the indices for
BMD (Yamazaki et al., 1992). The densitometer was self-managed by the subjects using thephantom of the heel once a week or more. The
accuracy of the densitometer was examined in 5
volunteers by measuring their BMD 3 times a
week: the coefficient of variation we observed
was 2.0 ± 1.3%. Fifty-five girls voluntarily applied, and their BMD was measured in July
1997 (Fig. 1); at the same time, we requested
them to fill out questionnaires and to be interviewed by us. At the end of the session, BMD
data were delivered to respective girls together
with guidance booklets containing an explanation of the onset mechanism of osteoporosis, theneed to increase BMD and methods for getting
the maximum level, for example, eating foods

rich in Ca, protein or vitamin D, taking substances which inhibit Ca assimilation, andunderstanding the need for exercise and sunbathing (1st guidance).
The questionnaire covered the following
topics: i) condition of the body and health—height, weight, age of menarche and regularity
in the menstrual cycle; ii) life-style—smoking
or nonsmoking, frequency of taking alcohol andcoffee, and duration of sunbathing, and iii) the
kind of exercise, its duration and frequency.
During the personal interview, we focused on
the kind and amount of foods they had taken the
day before.

Second-grade BMD measurement and2nd guidance
In July 1998, we measured BMD again in thesame subjects. Personal data and another booklet were delivered similarly at the end of themeasurement. The contents of the booklet
showed Ca-rich foods and recipes (2nd guidance).

Intervention in diet
As for the BMD index, we used stiffness of thebone calculated from the combined data of
speed of sound (SOS) and broadband ultrasound attenuation (BUA); the mean for 20-

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Bone density in adolescent girls

year-old Japanese females is 92 (Yamazaki etal., 1992). From the 2nd-grade students, weselected 19 girls with stiffness lower than 92(Fig. 2), and explained the method of intervention. We obtained consent from 11 girls, andcarried out the following intervention in theirdiet (intervention group; n = 11): i) the subjects
recorded the kind and amount of Ca-rich foods
they ate every day for 4 weeks; ii) we collected
the data once a week, calculated Ca intake, andtold them the results; and iii) as we informed
them of the data, we encouraged their efforts
and got them to confirm the next week’s goal by
discussing with them. Twelve weeks after, we
re-measured BMD.
The name and daily intake of Ca-rich foods
we requested the students to write were fish, sea
weed, cow milk, dairy products, tofu, small fry,
komatsuna, leaves of Chinese white radish andturnip and other brightly colored vegetables.
We calculated their Ca intake every week, andtold them how excessive or insufficient they
were from the daily amount necessary foradolescent Japanese girls (600 mg). In the caseof insufficiency, we advised those students to
set a goal for the next week where they could
resolve the insufficiency.

12Intervened
group selected

8

In July 1999, BMD was measured again when
the students were in the 3rd grade. This time,
we randomly selected 10 girls (non-intervention group) from those whose stiffness in the
2nd grade exceeded 92 (mean at 20 years ofage). Stiffness ranged from 92 to 111 in the
non-intervention group (n = 10), and from 67 to
87 in the intervention group (n = 11) (Fig. 1).
The amounts of food elements were calculated with a computing program NUTAS 4(Nankodo, Tokyo, Japan). Statistical analysis
was done with software StatView, Version 4(Abacus Concepts Inc., Berkeley, CA).

Results

First-grade BMD and affecting factors
The 55 girl students showed a mean (± SD) of
98.64 ± 11.63 for stiffness (Fig. 3).
Physical conditions, health and BMD
The subjects ranged from 18 to 20 years inage, 147 to 171 cm in height (mean, 157.5 cm)
and 41 to 63 kg in weight (49.9 kg). The mean
age of menarche was 12.4 years. The menstrual
cycle was “quite irregular” in 11 girls, “some-

Critical levels

115

Below mean andabove lowest normal

110

P < 0.01

105

6

Stiffness

Number of subjects

10

Third-grade BMD measurement

4

2

100
95
90
85
80

0
50

60

70

80

90

100

110

120

130

140

Stiffness
Fig. 2. Number of subjects classified by stiffness. Subjects forthe intervention group were selected from girls with criticallevels (67–79) and with levels above the lowest normal andbelow the mean at 20 years of age (80–87).

105

1st grade 2nd gradeFig. 3. Change in stiffness of 55
female subjects measured in the 1st
and the 2nd grades. Shown aremean ± 1SD. The difference issignificant (P < 0.01).

K. Minamimae et al.

times shortened or lengthened” in 29 girls and“regular” in 15 girls. Stiffness showed no significant relation to body height, weight or menarche. There was no significant difference between the mean for stiffness and regularity inmenstrual cycle.

Foods and BMD
We observed 404.9 ± 284.4 mg as the dailymean (± SD) of Ca intake, which showed nosignificant relation to stiffness.

Life-style and BMD
Among the 55 subjects, there was a habitual
smoker (“I smoke every day”), and the remaining 54 students were nonsmokers. The frequency of drinking alcohol was “once or twice aweek” in 4 girls and “sometimes” in 30 girls; 21
girls did not drink. The habit of coffee drinking
was “negative” in 11 girls, “sometimes” in 23
girls, “1 to 2 cups a week” in 11 girls and “3 to 5
cups a week” in 10 girls. The daily total of sunbathing was less than 60 min in 34 girls, and 60
min or more in 21 girls. The frequency of smoking, drinking alcohol or coffee drinking and theduration of sunbathing showed no significant
differences according to stiffness.

Stiffness data obtained 1 year later in the 2nd
grade was 94.38 ± 11.62 (Fig. 3). We performed a t-test for the data matched to both the 1st
and 2nd grade measurements, and observed asignificant decrease in BMD (t = 4.713, degrees
of freedom = 54, P < 0.01).

Exercise and BMD
Thirteen girls participated in sports, but therelation between stiffness and quantity of
exercise (severity × duration × weekly frequency) was not significant.
110
105Second-grade BMD measurement

BMD changes in the intervention and nonintervention groups
In the intervention group (n = 11), the stiffness
measured in July of the 2nd grade (80.0 ± 5.24)
and after 12 weeks (82.36 ± 3.85) showed a significant increase (P < 0.05). But the difference
between July of the 2nd grade and July of the
3rd grade (85.55 ± 7.15) was not significant(Fig. 4). The non-intervention group (n = 10)
recorded mean stiffness at 98.60 ± 7.29 in Julyof the 2nd grade and 97.20 ± 9.72 in July of the
3rd grade (Fig. 3).
The mean Ca intake on the previous day of
BMD measurement in July of the 3rd grade was
587 ± 258 mg in the intervention group and 592± 210 mg in the non-intervention group.

100

Stiffness

95

Discussion

90
85

We carried out BMD measurements over a 2year period for college girls, giving them active
instructions on life-style, and followed-up theeffects of our intervention on their diet.
As for methods of measuring BMD, the literature has reported roentogenography and ultrasound bone densitometry. We calculated levels ofstiffness for the present study with the lattermethod which served as the index for BMD.

80
75
70

P < 0.05

65
60

July Extra

July

2nd grade 3rd gradeFig. 4. Change in stiffness of the intervention group( , n = 11) and non-intervention group ( , n = 10)
measured in July of the 2nd grade (both groups),
extra (12 weeks after the measurement in July;
intervention group) and in July of the 3rd grade (bothgroups).

BMD and life-style
For the 1st grade, stiffness in 55 girls (aged 18
to 20 years) was higher than the age-matched

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Bone density in adolescent girls

mean reported in the literature (Yamazaki et al.,1992) (Fig. 3). The 55 girls responded to ourrecruitment out of a whole grade of college students consisting of 80 girls. We suppose thatthe voluntary subjects were concerned with
their health condition.
In the present study, we observed that difference in stiffness was not significant in comparing cases with or without any BMD-affecting factor. A significant correlation was reported between continuous sports activity and stiffness of the os calcis of 18- to 20-year-old Japanese women (Hasegawa et al., 1997). We observed no significant difference between stiffness and quantity of exercise in the present
study, which may be attributed to the low number of studied subjects. However, the dailymean of Ca intake calculated from personal
interviews concerning 1-day meals (404.9 ± 284.4mg) was 67.5% of the recommended daily level(600 mg). In a study of age-matched students at
a domestic science college (Kamezaki and
Shimao, 1994), the mean Ca intake was 408 ±179 mg (68% of necessary level). Both populations presented similar levels. These facts
suggest the necessity of nutrition betterment inadolescent Japanese females.

Change in stiffness between the 1st andthe 2nd grades
We performed a t-test for the data of stiffness
matching both the 1st and 2nd grades, and observed a significant decrease in stiffness (P <0.01). The peak of BMD in Japanese females is
15 to 17 years of age (Io et al., 1997). As the present subjects were aged 18 to 20 years, their peakof BMD had passed, which is one reason for thesignificant decrease we observed. Another presumable factor for BMD decrease is poor eating
habits in the population. BMD in July of the 1st
grade reflected eating habits administered bytheir families, but levels measured thereafter
were a reflection of poorly self-managed eating
habits. Following college entrance as new students, they started to live independently fromtheir family and prepared meals by themselves.
Their lack of cooking knowledge, skill and time
apparently produced trouble in their diets.

Health guidance to improve and maintain BMD
In the 1st guidance, we delivered the students abooklet on life-style methods for preventing
osteoporosis. However, 2nd-grade BMD decreased, which implies a correlation between
negative effects and the 1st guidance. To study
the individual’s subjective state of readiness totake recommended preventive health action,
Pender (1996) introduced the illustrated“Health Belief Model,” which was a reportdone by Becker et al. (1977). This model contained the following elements: i) the individual’s subjective state of readiness to take action
is determined by the individual’s perceived
likelihood of susceptibility to the particularillness, and ii) the individual’s estimate of theaction’s potential benefits in reducing susceptibility weighs against his perception of barriers
involved in the proposed action. As the aim of
the present study, we first explained to the subjects as follows: to prevent osteoporosis andbone fracture after menopause which is a highrisk in women with low BMD, it is important toincrease the maximum BMD in adolescenceand for young girls to take measures to reinforce
the habit of taking Ca. We lectured them on thisat the 1st guidance. Thus, our lecture on theimportance of Ca-taking behavior focused onhealth maintenance after menopause. Presumably, the students hardly recognized suchdisease-oriented concern as Pender (1996) suggested, and they did not realize the problem tobe related to their own possible future condition.
On the other hand, BMD did not change orincrease between the 2nd and the 3rd grades(Fig. 4). We supposed that the girls’ behavior
must have changed during the period: they
were shocked by the decrease in BMD between
the 1st and the 2nd grades, which was translated
as fear and which led them to perceive thatstrengthening the bone would be their benefit.
This is a result of effectively applied knowledge
obtained from our explanation.
According to Yamada et al. (1999), establishment of any behavior is the result of forming

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K. Minamimae et al.

motivations through the mutual functioning of
biological, psychological and social factors. In
the present study, the biological factor was the
BMD data, while the psychological factor was
students’ response to how they accepted thedata. The social factors considered were many:
the method of getting food, economical problems or encouragement by others. We intervened in the poor-BMD group for 4 weeks bymeans of appreciating girls’ efforts and confirming the following week’s goal; our intervention must have contributed to the forming of
motivation, which was the social factor in thepresent study. If intervention had made subjects feel like they were bearing a heavy burden,
however, the intervention would have had the
opposite effect to what was intended. We performed the above intervention for 12 weeks in aprevious study and observed some effects,
which lasted temporarily. One year after, during the 2nd-grade measurement, their Ca intake
returned to the pre-intervention level (Maeda
and Kitagawa, 1997). This fact suggests thatthe quantity and duration of intervention need
to be more fully considered.
Our conclusion is that girl students can andmust sustain their efforts to take Ca-rich food,when their knowledge of osteoporosis works
together with the recognition that Ca-taking
behavior is essential for their future.
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Received August 17, 2000; accepted September 18, 2000
Corresponding author: Prof. Takako Maeda