Original Paper.
Biomedical Human Kinetics, 2, 81 – 84, 2010
DOI: 10.2478/v10101-0020-z
The effect of milk consumption on bone mass density in obese and
thin adult women
Nasim Habibzadeh
Department of Exercise Physiology, University of Guilan, Rasht, Iran
Summary
Study aim: To assess the effect of milk consumption lasting two months on BMD of obese and thin young women.
Material and methods: A group of 38 untrained women (18 obese [O] – BMI>30, and 20 thin [T] – BMI<20), aged
20 – 25, years participated in the study. They were randomly assigned into BMI-matched experimental [E] or control [C] groups containing 9 obese and 10 thin subjects each. Experimental groups were given 2 glasses of milk (600
mg/day of calcium; fat content 1.5%) for 2 months, 3 days a week. At the beginning (Pre) and at the end (Post) of
the study, bone mass density (BMD) at the hip and spine (L2-L4) was measured using DEXA technique, and oestrogens, calcium and phosphorus were determined in serum. Body fat content (%F) and lean body mass (LBM) were
determined using the bioimpedance (BIA) technique.
Results: In both experimental groups BMD significantly (p<0.05 – 0.001) increased in both areas by 4 – 7%. In the
TE group, %F significantly (p<0.05) decreased by 8% and LBM significantly (p<0.001) increased by 3%. Serum
calcium decreased in all groups except OC by 3 – 5% (p<0.05 – 0.01) and oestrogens markedly increased in all groups
except TC.
Conclusion: The data suggest that adequate milk intake (thus calcium) in adolescence is an indicator of attaining
adequate bone mass density, thus preventing the risk of osteoporosis.
Key words: Osteoporosis – Bone mass density – Milk – Obesity
Introduction
Bone calcium stores remain open for a relatively
short period of life. Calcium is a critical component of
bone mass and of reducing the risk of bone fractures,
especially those due to osteoporosis [12]. As noted by
Heaney [6], dairy products contain many essential nutrients, milk and milk products being the major source of
calcium in the diet and provide other important bonebuilding compounds including vitamin D, protein, potassium and phosphorus. Many studies examined the
effects of milk on bone health in children and adolescents [9].
A number of retrospective studies showed a link between low milk consumption during the childhood and
adolescence and decreased bone mineral density (BMD)
in young women, premenopausal women and older postmenopausal women. In a recent study on Chinese adolescent girls aged 12 – 14 years (n = 649) [3], milk intake was found to be positively associated with distal
Author’s address
radius and ulnar bone mass, milk accounting for 3.2%
of the total BMD variation . However, other studies reported a negative effect of milk and dairy products on
bones; Feskanich et al. [5] did not support the hypothesis that consumption of milk or of other dietary sources
of calcium by adult women protected against hip or forearm fractures.
There is evidence that milk consumption decreased
over the last decades in many countries. In most of them
more than half of the dietary intake of calcium comes
from milk, young people being of particular concern.
Calcium intake is important to bone health throughout
life and milk continues to be the most important source,
particularly under unfavourable physiological conditions,
such as achlorhydria. A long-term avoidance of milk is
associated with low stature and poor bone health of
adult women. Forearm fracture rates of children and
adolescents increased sharply in recent years, and many
researchers attributed that to falling milk consumption
and displacement of milk by carbonated drinks [4].
Nasim Habibzadeh M.S., Department of Exercise Physiology, University of Guilan, Rasht, Iran
[email protected]
Unauthenticated
Download Date | 6/17/17 9:43 PM
N. Habibzadeh
82
Dietary milk (and, thus, calcium) intake at some ages
may influence bone mineral indices at specific sites during the development of peak bone mass but no report
was found in the available literature about the effect of
milk consumption on bone mass density (BMD) in young
women. The aim of this study was thus to assess the effect
of milk consumption lasting over 2 months on BMD of
adult obese and thin women.
Material and Methods
Subjects: A group of 38 untrained women aged 20 –
25 years volunteered to participate in this study. This included 18 obese (BMI>30) and 20 thin (BMI <20) subjects. The participants were randomly assigned into experimental and control groups, each consisting of 9 obese
and 10 thin, BMI-matched subjects. All subjects submitted their written consents to participate prior to the study
which was approved by the local Committee of Ethics.
All subjects underwent medical examinations prior to
the study and were found clinically healthy (no cardiovascular, musculoskeletal, respiratory, or other chronic
diseases that might limit training or testing), had no menstrual irregularities, were not using any beta-blockers or
medication that might influence bone mass density, led
a sedentary life (no regular sports activities for at least 2
years), were not dieting and not smoking. During the
study, both experimental groups received two glasses of
milk (600 mg/day of calcium; fat content 1.5%) for two
months, 3 days a week. Control subjects received no milk
or specific diet. All subjects were requested to continue
their sedentary lifestyle throughout the research period.
At the beginning (baseline, Pre) and at the end (Post) of
it the subjects underwent the examinations listed below.
Methodology: Body mass and height were recorded and
body mass index (BMI) was computed. Body fat content was determined using a bioelectrical impedance
device (BIA-106, RJL Systems, USA). Body mass was
recorded every week; changes in body mass did not
exceed 2.2 kg throughout the study.
Bone mass density (BMD) at the hip and at lumbar
spine (L2 – L4) was measured with the dual X-ray absorptiometry scans (DXA; Norland XR-26, WI, USA).
All the scannings and analyses were done by the same
operator. The day-to-day variability of BMD measurements ranged from 0.7 to 1.7%.The scanner was calibrated daily, its performance being monitored using the
quality assurance protocol. No significant machine drift
was noted throughout the study.
Blood samples were collected after an overnight fast
(>12 h) in sitting position and centrifuged at 1500 rpm
for 30 min at 4oC within 2 h. Serum samples were stored
frozen at -20o C until assayed.. Serum oestrogens were
determined by radioimmunoassay (Amersham Biosciences, Piscataway, NJ, USA) in the follicular stage of
subject’s menstrual cycle; calcium and phosphorus levels
were determined in serum by standard automated laboratory techniques.
Prior to the study, subjects from the experimental
groups were instructed on the diet by a licensed dietician
according to the American Health Association (AHA) in
order to minimise any effects that dietary composition
might have on the measured metabolic variables. The recommended diet contained 50 – 55% of carbohydrates,
15 – 20% of protein and less than 30% of fat. The subjects were requested to maintain this diet composition
throughout the two months of study and this was monitored by 7-day recalls taken every week [8]. Both experimental groups received two glasses of milk (600
mg/day of calcium; fat content 1.5%) for two months, 3
days a week. Control subjects groups received no milk
or specific diet; they were requested to continue their
sedentary lifestyle throughout the research period.
Table 1. Mean values (±SD) of somatic variables before (Pre) and after (Post) training programme
Variable
Group
Obese (n = 9)
Thin (n = 10)
Obese (n = 9)
Thin (n = 10)
Age
(years)
Experimental
Pre 22.2 ± 1.9
Post
Pre 21.1± 1.7
Post
Control
Pre 22.6 ± 1.5
Post
Pre 21.9 ± 1.2
Post
-
Body
height (cm)
Body mass
(kg)
BMI
Body fat
content (%)
Lean body
mass (kg)
157.7 ± 5.1
159.9 ± 7.5
Control
159.1 ± 1.5
162.7 ± 6.6
-
75.0 ± 8.1
73.3 ± 7.7***
45.9 ± 5.3
46.4 ± 5.2
30.2 ± 1.8
29.2 ± 2.1*
17.8 ± 1.2
17.8 ± 1.5
38.8 ± 4.0
36.4 ± 6.8
21.8 ± 3.1
20.1± 3.6*
43.3 ± 5.3
44.4 ± 6.2
33.5 ± 3.7
34.5 ± 4.0***
78.1 ± 10.9
78.1 ± 10.1
46.5 ±5.7
46.3 ± 5.2
30.9 ± 3.3
30.3 ± 3.2
17.5 ± 1.1
17.6 ± 0.1
39.7 ± 3.5
39.0 ± 5.2
22.4± 2.9
22.4 ± 3.2
43.9 ± 6.0
44.3 ± 6.7
33.9 ± 4.3
33.7 ± 4.1
Significantly different from the respective ‘Pre’ value: * p<0.05; *** p<0.001
Unauthenticated
Download Date | 6/17/17 9:43 PM
Milk consumption and bone mass density in women
Data analysis: The SPSS 11.5 for Windows software
was used. Student's t-test for dependent variables was
applied to assess the Post-Pre changes in studied variables, the level of p<0.05 being considered significant.
Results
Few changes were noted in the somatic variables
(Table 1). The obese subjects from experimental group
(OE) significantly (p<0.001) reduced their body mass
by 2% and BMI by 3%. In the TE group, %F signifi-
83
cantly (p<0.05) decreased by 8% and LBM significantly
(p<0.001) increased by 3%.
As shown in Table 2, the BMD values at the spinal
(L2 – L4) and lumbar regions significantly increased in
both experimental groups by 4 – 7% (p<0.05 – 0.001).
The global increments in BMD were not correlated
significantly with any variable recorded. Serum calcium
decreased in all groups except OC by 3 – 5% (p<0.05 –
0.01) and oestrogens markedly increased in all groups
except TC.
Table 2. Mean values (±SD) of bone mass density (BMD) and biochemical variables before (Pre) and after (Post)
study period
Variable
Group
Obese (n = 9)
Thin (n = 10)
Obese (n = 9)
Thin (n = 10)
Hip BMD
(g/cm2)
Experimental
Pre
0.929 ± 0.107
Post
0.967 ± 0.095***
Pre
0.820 ± 0.060
Post
0.863 ± 0.064**
Control
Pre
0.958 ± 0.086
Post
0.964 ± 0.092
Pre
0.834 ± 0.115
Post
0.831 ± 0.107
Spine (L2– L4)
BMD (g/cm2)
Oestrogen s
(pg/ml)
Calcium
(mg/dl)
Phosphorous
(mg/dl)
1.113 ± 0.168
1.160± 0.155*
1.051 ± 0.147
1.128 ± 0.216*
Control
1.247 ± 0.174
1.233 ±.142
1.057 ± 0.121
1.060 ± 0.135
30.4 ± 15.6
61.0 ± 18.6***
25.6 ± 8.4
60.2 ± 18.8***
Control
23.9 ± 13.1
41.5 ± 17.2*
33.0 ± 14.3
38.0 ± 10.6
9.47 ± 0.24
9.42 ± 0.26*
9.78 ± 0.42
9.25 ± 0.50**
3.80 ± 0.39
3.66 ± 0.64
4.21 ± 0.40
3.55 ± 0.37**
9.50 ± 0.46
9.39 ± 0.31
9.67 ± 0.31**
9.28 ± 0.32
3.84 ± 0.47
3.53 ± 0.44
3.96 ± 0.54
3.80 ± 0.39
Significantly different from the respective ‘Pre’ value: * p<0.05; ** p<0.01; *** p<0.001
Discussion
This study demonstrated the effects of regular milk
consumption on the bone status in young women considered to be at risk of osteoporosis. The evident improvement in bone mass density could be attributed to the
milk calcium intake inasmuch the lack of vitamin D
measurements was a serious limitation in this study. The
improvement could have been enhanced by the young
age of subjects.
Several authors studied the effects of milk or calcium
intake on BMD in premenopausal women but the results
were equivocal. Kalkwarf et al. [7] found that regular
milk consumption apparently protected against later
bone fractures and improved bone mass; similar effects
were also reported by Soroko et al. [11] for young and
adult subjects. In another study [1], adolescent girls who
consumed 300 ml of milk daily for 18 months had significantly higher BMD compared with the control group
(by 9.6 vs. 8.5%) and significantly higher bone mineral
content (BMC; by 27 vs. 24%).
Renner [10] recommended daily calcium intake by
subjects aged 10 – 24 years to amount to 1200 mg in
order to protect against bone resorption, as evidenced by
reduced serum osteocalcin, a marker of bone turnover.
On the other hand, Woo et al. [13] studied Chinese women
aged 20 – 35 years who consumed powdered milk (daily
calcium intake equal to 1000 mg) for two years and
found little difference in various factors compared with
control subjects except significantly higher BMD at the
spinal region. They attributed the non-consistent results
to age-related differences in bone metabolism and to a
lack of compliance.
Inasmuch most subjects would agree milk is a healthy
choice, they may believe it also holds risks because of
additives or processing and calcium may come just as
easily from other sources. Some authors suggest that
calcium supplements do not bring the same benefits as
calcium from dairy products and although supplementing calcium at a dose of 1 g daily significantly delayed
or even prevented bone loss in post-menopausal women,
very little work was done in the young ones.
Unauthenticated
Download Date | 6/17/17 9:43 PM
N. Habibzadeh
84
It was reported [2] that a higher consumption of dairy
products at 20 years of age was associated with an increased risk of hip fracture in men and women aged 65
years and above, and similar results were found in the
USA Nurse's Health Study following over 72 000 women
for 18 years showing no protective effect of increased
milk consumption against bone fracture risk.
Yet, this study showed that two glasses of milk daily
(600 mg calcium) consumed for 3 days a week resulted
in increasing BMD in young, adult women. Frequent
milk consumption at the age of 25 years improved the
lumbar and spinal bone mass. In addition, regular milk
consumption in the childhood may contribute to continuing that habit later in life. Thus, the hypothesis that
adequate calcium intake in milk at adolescence is an
indicator of attaining adequate bone mass density, thus
preventing the risk of osteoporosis.
References
1. Cadogan J., R.Eastell, N.Jones, M.Barker (1997) Milk
intake and bone mineral acquisition in adolescent girls: randomized controlled intervention trial. Br.Med.J. 315:1255-1260.
2. Cumming R.G., R.J.Klineberg (1994) Case-control study
of risk factors for hip fractures in the elderly. Am.J.Epidemiol.
139:493-503.
3. Du X.Q., H.Greenfield, D.R.Fraser, K.Y.Ge, Z.H.Liu,
W.He (2002) Milk consumption and bone mineral content in
Chinese adolescent girls. Bone 30:521-528.
4. Feskanich D., W.C.Willett, M.J.Stampfer, G.A.Colditz
(1997) Milk, dietary calcium, and bone fractures in women: a
12-year prospective study. Am.J.Public Health 87:992-997.
5. Feskanich D., W.C Willett, G.A.Colditz (2003) Calcium,
vitamin D, milk consumption, and hip fractures: a prospective
study among postmenopausal women. Am.J.Clin.Nutr. 77:504-511.
6. Heaney R.P. (2000) Calcium, dairy products and osteoporosis. J.Am.Coll.Nutr. 19:83S-99S.
7. Kalkwarf H.J., J.C.Khoury, B.P.Lanphear (2003) Milk
intake during childhood and adolescence, adult bone density,
and osteoporotic fractures in US women. Am.J.Clin.Nutr. 77:
257-265.
8. New S.A, C.Smith, D.A.Grubb, D.M.Reid (1997) Nutritional influence on bone mineral density: a cross-sectional study
in premenopausal women. Am.J.Clin.Nutr. 65:1831-1839.
9. Peter C.E. (2005) Time to value milk. Int.J.Epidemiol.
34:1160-1162.
10. Renner E. (1994) Dairy calcium, bone metabolism, and
prevention of osteoporosis. J.Am.Dairy Sci.Assoc. 77:34983505.
11. Soroko S., T.L.Holbrook, S Edelstein, E.Barrett (1994)
Lifetime milk consumption and bone mineral density in older
women. Am.J.Public Health 84:1319-1322.
12. Sambrook P., C.Cooper (2006) Osteoporosis. Lancet
367:2010-2018.
13. Woo J., W.Lau, L.Xu, C.Wai Kei Lam, X.Zhao, W.Yu,
X.Xing, E.Lau, B.Kuhn-Sherlock, N.Pocock, R.Eastell (2007)
Milk supplementation and bone health in young adult Chinese
women. J.Women's Health 16:692-702.
Received 12.08.2010
Accepted 12.10.2010
© University of Physical Education, Warsaw, Poland
Acknowledgments
The work was supported by grants from the University of
Guilan
Thanks are due to all the subjects who participated in this
investigation
Unauthenticated
Download Date | 6/17/17 9:43 PM