-12 -8 -4 0 4 8 12

% Difference in Hip BMD

Association of selected lifestyle factors with BMD

Adjusted mean BMD* N Hip Spine Whole Body

__________________________________________________________________

Current Yes 39 0.935 0.969 1.069smoker No 135 0.968 0.987 1.088

(p=0.12) (p=0.40) (p=0.30)

Wt-bearing 0-<55 62 0.947 0.965 1.069activity 55-<70 62 0.962 0.997 1.086

70+ 50 0.976 0.986 1.099 (p=0.39) (p=0.26) (p=0.26)

Dietary 0-<650 60 0.944 0.972 1.072Calcium 650-<1300 53 0.971 0.986 1.071(mg/day) 1300+ 52 0.970 0.992 1.109

(p=0.30) (p=0.58) (p=0.06)

Dietary 0-<45 44 0.953 0.960 1.087Protein 45-<90 90 0.951 0.976 1.078(gm/day) 90+ 31 0.999 1.035 1.095

(p=0.26) (p=0.15) (p=0.70)

Dietary 0-<180 59 0.958 0.962 1.066Magnesium 180-<360 83 0.952 0.976 1.072(mg/day) 360+ 23 0.999 1.058 1.169

(p=0.29) (p=0.04) (p=0.002)

Any caffeine Yes 104 0.952 0.981 1.080intake No 70 0.973 0.986 1.089

(p=0.20) (p=0.77) (p=0.58)

Caff. cola 0-1 123 0.969 0.985 1.095(drinks/day) 2+ 50 0.938 0.978 1.053

(p=0.12) (p=0.72) (p=0.01)

Alcohol 0 74 0.954 0.978 1.078(drinks/mo) <5 62 0.969 0.996 1.098

5+ 38 0.960 0.970 1.072 (p=0.71) (p=0.44) (p=0.31)

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* Adjusted for the following baseline covariates: age, height, weight, and calcium as continuous variables; ethnicity, number of periods in last year and hormone-based contraception as categorical variables.

mean ± s.e. median HIP BMD

Spearman correlation

Age at menarche (yrs.) 12.3 ± 0.1 12.0 0.05

Height (in) 64.1 ± 0.2 64.1 0.29*

Weight (lb) 142.4 ± 2.2 137.1 0.42*

Weight-bearing activity 61 ± 1 61 0.25*

Calcium (mg/day) 973 ± 47 833 0.11

Protein (gm/day) 66 ± 3 59 0.09

Magnesium (mg/day) 235 ± 9 220 0.09

Caffeine (mg/day) 52 ± 6 20 -0.10

Calories (kcal) 1717 ± 66 1593 -0.006

_______________________________________________________________________________

*p< 0.05

Study Setting Group Health Cooperative (GHC), a mixed-model HMO located in Washington state

Study Design Cross-sectional

Participants 174 adolescent women, ages 14-18 yearsSelected using computerized databases from this health plan

Inclusion/ Not pregnant or lactating, post-menarche, no Exclusion conditions or medications that might affect bone

density, informed consent from parents for participants <18

Data Collection Health questionnaire; Food frequency questionnaire; Exam; DEXA

Lifestyle Factors Current smoking; weight-bearing physical activity; dietary intake of magnesium, calcium, protein, alcohol, caffeine and caffeinated cola beverages

Outcome Hip, spine, and whole body bone mineral density (g/cm2) using DEXA

Analyses Association of lifestyle factors with BMD, after adjustment for the effects of age, height, weight, ethnicity, number of periods in the past year,

hormonal contraception, and dietary calcium

All study procedures were reviewed and approved by the GHC Human Subjects Committee

Lifestyle Factors Associated with Bone Mineral Density in Adolescent WomenDelia Scholes1,2, Andrea Z. LaCroix1,2 , Laura E. Ichikawa1, Susan M. Ott2, William E. Barlow1,2

1Group Health Cooperative and the 2University of Washington, Seattle WA

INTRODUCTION

Background

Maximizing peak bone mass is essential for prevention of future morbidity from osteoporosis.

Adolescence is a particularly critical time for bone mass accrual. More than half of peak bone mass is attained during adolescence and, for many anatomic sites, bone mass accrual is virtually complete by age 18.

Heritable factors are most important in peak bone mass attainment. But identification of modifiable risk factors offers opportunities for interventions aimed at improving bone health.

A number of lifestyle factors, including dietary factors, smoking, and exercise, have been both positively and negatively associated with bone density.

Purpose

To evaluate the association between selected lifestyle factors and bone mineral density in a population-based study group of adolescent women.

METHODS

RESULTS

Summary of Results

A number of biologic and lifestyle variables were associated with bone density as the hip or other anatomic site.

However, after adjusting for other factors known to affect bone density, the majority of the lifestyle factors we examined were not significantly associated with BMD in these adolescents.

Two dietary factors, magnesium and caffeinated cola consumption, were significantly associated with BMD in this study group:

• Dietary intake of magnesium was positively associated with BMD at two anatomic sites, the spine and whole body.

• Consumption of caffeinated cola beverages was negatively associated with whole body BMD.

CONCLUSIONS

When compared to inherited and hormonal influences, lifestyle factors may have relatively modest effects on bone density and bone mass accrual in essentially healthy adolescent women.

Studies of these factors to date have had inconsistent methods and findings.

Future prospective studies or randomized trials of sufficient size are needed to determine whether these factors in adolescents can be modified to improve bone health.

This research supported by The National Institutes of Health (NICHD, R01HD31165)

Selected Baseline Characteristics

Total hip BMD, g/cm2 0.956 ± 0.009

Spine BMD, g/cm2 0.982 ± 0.009

Whole body BMD, g/cm2 1.082 ± 0.008

Magnesium 180-<360 mg/day (vs. <180)

Calcium 1300+ mg/day (vs. <650)

Calcium 650- <1300 mg/day (vs. <650)

Wt. Bearing activity score 70+ (vs. <55)

Wt. bearing activity score 55-<70 (vs. <55)

Age 16-18 (vs. 14-15)

Non-white

BMI <18.5 (vs. normal)

BMI 25-<30 (vs. normal)

BMI 30+ (vs. normal)

0-7 periods (vs. 8+)

Ever pregnant

Hormonal contraception

Magnesium 360+ mg/day (vs. <180)

Smoker

<5 alcoholic drinks/mo (vs. 0)

5+ alcoholic drinks/mo (vs. 0)

2+ caff. cola drinks/day (vs. 0-1)

Personal fracture

Correlation between selected variables

Wt. bearing Calcium Protein Magnesium Caff. Cola Alcohol activity

_______________________________________________________________________________

Wt bearingactivity 0.24* 0.27* 0.28* -0.23* -0.09

Calcium 0.87* 0.87* -0.14 0.02

Protein 0.88* -0.11 -0.002

Magnesium -0.20* 0.005

Caff. Cola 0.18*_______________________________________________________________________________

Age -0.09 -0.05 -0.01 0.03 0.11 0.22*

BMI -0.05 -0.07 -0.09 -0.09 0.14 0.07_______________________________________________________________________________

*p< 0.05