Effects of coffee consumption and smoking habit on bone mineral density

Role of lifestyle factors in mediating the effect of educational attainment on bone mineral density: a Mendelian randomization study

We performed two-step multivariable Mendelian randomization analysis to explore the mediating role of lifestyle factors in educational attainment (EA) and bone mineral density (BMD). Summary statistics from genome-wide association studies of European lineages were used. Coffee intake and processed-meat intake mediated the association between EA and BMD.

PURPOSE

This study aimed to explore the causal relationship between educational attainment (EA) and bone mineral density (BMD), as well as the potential mediating roles of lifestyle factors in the expected EA-BMD relationship. By identifying modifiable lifestyle factors, we hope to provide relevant information to prevent osteoporosis or low BMD in the less educated population.

METHODS

Using summary statistics from genome-wide association studies (GWAS) of major European lineages, one- and two-sample Mendelian randomization (MR) analyses were performed to estimate the association between EA (in the social sciences genetic association consortium (SSGAC) involving 766,345 individuals and in the UK Biobank (UKB) involving 293,723 individuals) and BMD (in the Genetic Factors for Osteoporosis Consortium involving 426,824 individuals selected from the UKB). The EA variable in both consortia were expressed by years of schooling completed. Two-step multivariable MR was used to assess the mediating roles of eight lifestyle-related factors (moderate-to-vigorous physical activity, watching television, computer using, smoking initiation, coffee intake, alcohol intake frequency, tea intake, and processed-meat intake) in the EA and BMD association, and the corresponding mediating proportion was calculated. Meta-analysis was used to present a pooled estimate.

RESULTS

A total of 317 and 73 independent single-nucleotide polymorphisms (SNPs) of GWAS significance (P < 5.0 × 10-8) were selected as instrumental variables (IVs) for EA in the SSGAC and UKB, respectively. A total of 513 SNPs were selected as IVs for the BMD. The results of one- and two-sample MR revealed that the genetically predicted BMD increased by 0.094 and 0.047 g/cm2, respectively, in response to each SD increment of genetically predicted schooling years. Among the eight candidate mediators, coffee intake and processed-meat intake were potential mediators revealed by the two-step multivariable MR analysis, mediating 26.87% and 23.92% of EA's effect on BMD, respectively. Meta-analysis showed consistent findings. Results of sensitivity analysis indicated the robustness of our findings.

CONCLUSION

We elucidated the causal protective effect of EA on BMD and the mediating roles of coffee intake and processed-meat intake. Intervening with these factors can potentially reduce the burden of bone density loss or osteoporotic fractures among the less educated population.

Association between caffeine intake and lumbar spine bone mineral density in adults aged 20-49: A cross-sectional study

Background

Many epidemiological studies have investigated the connection between coffee intake and bone mineral density (BMD), but the results are controversial. This study aimed to assess the association between caffeine consumption and lumbar BMD in adults aged 20-49.

Methods

From a cross-sectional study based on a large sample of the National Health and Nutrition Examination Survey 2011-2018. After controlling for confounders, the weighted multivariate linear regression model was created and stratified by age, gender, and race for subgroup analysis. In addition, we simultaneously stratified analysis by age and sex and divided caffeine intake into quartiles to assess the association between coffee intake and BMD.

Results

Caffeine intake was not significantly linked with lumbar BMD in this study of 7041 adults. In subgroup studies stratified by age, there was a significant correlation between lumbar BMD and caffeine consumption in participants aged 30-39 and 40-49. In females, there was a positive correlation between lumbar BMD and coffee consumption stratified by gender. When evaluated by race, the association between lumbar BMD and caffeine intake was independent of race. Consequently, when stratifying for age, sex, and coffee intake quartiles, a significant positive correlation was discovered between the fourth coffee intake quartile and lumbar BMD in females aged 30-39. In addition, a negative correlation was discovered between coffee consumption and lumbar BMD in males aged 40-49.

Conclusions

Our research indicates that drinking coffee may benefit 30-39 women's lumbar BMD, but it may adversely affect men aged 40-49.

The effects of caffeine on bone mineral density and fracture risk

Caffeine is a regular part of the diet of many adults (coffee, tea, soft drinks, and energy drinks). Multiple molecular effects of caffeine suggest that it may promote bone loss. Given the extensive consumption of caffeine worldwide, any impact of caffeine consumption on bone strength and/or density would have large population health implications. The most well-established pharmacological effect of caffeine is non-specific antagonism of adenosine receptors. Adenosine regulates bone metabolism in a complex manner, with in vitro studies suggesting that direct stimulation of adenosine A_2A and A_2B receptors induces bone formation by activating osteoblasts and suppressing osteoclast differentiation and function. Thus, competitive inhibition of adenosine A₂ receptors by caffeine may inhibit bone formation and promote bone resorption. However, antagonism of adenosine A₁ receptors may have opposing effects. Caffeine has also been suggested to affect bone through derangement of calcium metabolism, alteration of vitamin D responses, and other mechanisms. In clinical and population-based studies, the impact of caffeine consumption on bone metabolism offers a mixed picture, with some but not all studies suggesting a potential link between caffeine intake and reduced bone mineral density or increased fracture risk. Differences in methodology, selected populations, and duration/timing of the studies may account for study outcome discrepancies. The in vitro effects of caffeine on cells involved in bone metabolism suggest that caffeine intake may promote osteoporosis, and some but not all clinical studies support a modest adverse caffeine impact. Herein, we describe the basic biology of caffeine as it pertains to bone, review the clinical literature to date, and consider the implications of the current data on clinical practice and future studies.

Coffee consumption and caffeine intake in relation to risk of fractures: a systematic review and dose-response meta-analysis of observational studies

BACKGROUND

Conflicting reports are available about the association of coffee or caffeine intake and risk of fracture. We performed the current updated systematic review and dose-response meta-analysis of coffee consumption and caffeine intake and risk of fracture to quantify this association.

MATERIALS AND METHODS

PubMed/Medline, ISI Web of Science, and Scopus, Cochrane database were searched up to July 2021. Random-effects model or fixed-effects model was used to pool the study-specific effect sizes (ESs) and 95% confidence intervals (CIs). Dose-response relationship was examined using linear and non-linear dose-response analyses. The certainty of evidence was assessed using NutriGrade tool.

RESULTS

Out of 22 eligible studies included in the meta-analysis, 15 had cohort and 7 had case-control design. We found no significant association between coffee consumption and risk of fracture, either based on pooling cohort (RR: 0.99; 95% CI: 0.88, 1.12; I2 = 71.4%, Pheterogeneity < 0.01) or case-control studies (OR: 1.13; 95% CI: 0.87, 1.46; I2 = 49.0%, Pheterogeneity=0.08). In the subgroup analysis of cohort studies, we observed that higher coffee intake was inversely associated with risk of fracture in men (RR: 0.85; 95% CI: 0.76 to 0.94). In addition, a positive association was seen between coffee consumption and risk of fracture in studies with less than 12 years of follow-up (RR: 1.14; 95% CI: 1.02 to 1.27). With regard to caffeine intake, a statistically significant positive association was seen with risk of fracture (RR: 1.15; 95% CI, 1.08 to 1.23; I2=26.6%, n = 8). In the dose-response analysis, we found that each additional 100 mg caffeine intake was marginally associated with 2% greater risk of fracture (RR: 1.02; 95% CI: 1 to 1.05; I2= 70.3%, n = 6).

CONCLUSION

High coffee consumption was protectively associated with risk of fracture in men, while caffeine intake was positive associated with risk.

Secondary Prevention of Osteoporosis Through Assessment of Individual and Multiple Risk Factors

Introduction

Osteoporosis is a chronic progressive bone disease where the bone tissue resorption exceeds its regenerative capacities. Such a process leads to the reduction of bone mineral density (BMD), and distortion of trabecular microarchitectonics, which creates the basis for an increased fracture risk on a "low trauma" for osteoporosis patients. The notion of low trauma implies a stressor that will not cause a fracture in a healthy person under normal circumstances. BMD is a strong predictor of future fractures. However, many fractures occur in persons with BMD values beyond the defined osteoporosis threshold, and BMD measurement only partially identifies the part of the population with increased fracture risk. Also, it is known that risk factors are influencing the bone mass reduction as predictors of future fractures, and their association may lead to an increased fracture risk irrespective of the bone mass and T-score.

Aim

The 10-year individual risk assessment for osteoporotic fracture and the analysis of impact of individual and multiple osteoporosis risk factors on the degree of osteoporotic fracture risk.

Methods

The research is a retrospective-prospective study which analyzed 120 patients divided into two groups: 1) asymptomatic patients with known risk factors for osteoporosis in the age group of 40-65 (n=60), 2) asymptomatic patients with known risk factors for osteoporosis in the age group of 65-90 (n=60). FRAX® algorithm was used as a tool for the 10-year hip fracture risk assessment, with prior approval of the Centre for Metabolic Bone Diseases, University of Sheffield from the United Kingdom. Fracture risk assessment was calculated using the online FRAX® calculator. High risk is defined as the hip fracture risk higher than 3% or the risk of a "big" osteoporotic fracture higher than 20%. Results are expressed as mean values with a standard deviation. A comparison between tested patient groups was made applying the student T-test.

Results

32% of patients of average age of 65.8±12.6 years are under high hip fracture risk, 28% of patients are under the hip fracture risk higher than 3%, and the risk for 0.03% patients is higher than 20%. Patients with high fracture risk are of advanced age, female, with lower body weight and height values, lower bone mineral density (BMD) and T score values than patients who are not under a high fracture risk. A positive family anamnesis to osteoporosis and fractures, earlier fractures, smoking, rheumatoid arthritis, and use of glucocorticoids are risk factors that are more represented in patients with high fracture risk and osteoporosis. The impact of the majority of individual risk factors for osteoporosis and fracture is moderate, and their joint effect is significant. The contribution of individual risk factors to the overall 10-year fracture risk depends on the type, number and association of risk factors.

Conclusion

This research is a contribution to the resolution of polemics among authors, i.e. a dilemma whether persons with multiple clinical risk factors for osteoporosis with T score values beyond the defined threshold for osteoporosis are candidates for therapy with bisphosphonates, and a dilemma whether persons without any clinical risk factors for osteoporosis with T score values within the defined osteoporosis threshold require therapy with bisphosphonates, or only monitoring is sufficient.

Polyphenol-Rich Foods and Osteoporosis

BACKGROUND

Osteoporosis is a metabolic disease affecting the bone mineral density and thus compromise the strength of the bones. Disease prevention through diet is the objective of the study and discussion. Among the several nutrients investigated, the intake of phenols seems to influence bone mineral density by acting as free radical scavengers, preventing oxidation-induced damage to bone cells. In addition, the growing understanding of the bone remodelling process supports the theory that inflammation significantly contributes to the etiopathogenesis of osteoporosis.

METHODS

To provide an overview of current evidence on polyphenol-rich foods and osteoporosis prevention we made a comprehensive review of the literature focusing on the state of art of the topic.

RESULTS

Some polyphenol-rich foods, including olive oil, fruit and vegetable, tea and soy, seem to be beneficial for preventing osteoporosis disease and its progression. The mechanism is still partly unknown and may involve different pathways which include inflammation and other disease reactions.

CONCLUSIONS

However, further research is needed to better understand the mechanisms regulating the molecular interaction between osteoporosis incidence and progression and polyphenol-rich foods. The current evidence suggests that dietary intervention with polyphenol rich foods may be useful to prevent incidence and progression of this condition.

Does coffee drinking have beneficial effects on bone health of Taiwanese adults? A longitudinal study

Background

Results from studies investigating the association between coffee consumption and osteoporosis or bone mineral density (BMD) have been inconsistent. This longitudinal study was performed to assess the effect of coffee drinking on bone health of Taiwanese adults.

Methods

Data were retrieved from the Li-Shin (Landseed) Hospital in Taoyuan City. In 2006, 6152 participants completed a questionnaire on coffee drinking and other lifestyle factors. In 2014, 5077 of them were followed up. Nonetheless, a total of 2395 participants with incomplete data were excluded. The final analyses included 2682 participants comprising 1195 men and 1487 women (706 premenopausal and 781 postmenopausal). T-scores were derived from the osteo-sono assessment index (OSI) which is a surrogate of BMD. Coffee drinking was categorized as “no, medium, and high” based on the number of cups that were consumed per week in both 2006 and 2014.

Results

In general, medium and high coffee drinking were associated with higher T-scores. However, significant results were observed only among high drinkers (β = 0.158; P = 0.0038). Nonetheless, the test for linear trend was significant (P = 0.0046). After stratification by sex, medium and high coffee drinking were associated with higher T-scores. However, significant results were prominent only among high male drinkers (β = 0.237; P = 0.0067) and the test for trend was significant (P = 0.0161). Based on menopausal status, coffee drinking was associated with higher T-scores. Nevertheless, significant results were found only among premenopausal women (β = 0.233; P = 0.0355 and β = 0.234; P = 0.0152 for medium and high coffee drinking, respectively. The test for linear trend was significant (P = 0.0108).

Conclusion

Coffee drinking was significantly associated with higher T-scores hence, a lower risk of osteoporosis in men and premenopausal women.

Electronic supplementary material

The online version of this article (10.1186/s12889-018-6168-0) contains supplementary material, which is available to authorized users.

Vibration Therapy to Prevent Bone Loss and Falls: Mechanisms and Efficacy

A considerable volume of evidence has accumulated to suggest that whole-body vibration (WBV) may have a therapeutic role to play in the prevention of osteoporotic fracture, particularly for individuals who are unable to tolerate vigorous exercise interventions. There is moderate to strong evidence that WBV will prevent falls (likely due to enhanced neuromuscular function), but also some indication that the effects of WBV do not outstrip those of targeted exercise. Animal data indicates that WBV will also improve bone mass, including preventing loss due to hormone withdrawal, disuse and glucocorticoid exposure. Human trials, however, have produced equivocal outcomes for bone. Positive trends are apparent at the hip and spine, but shortcomings in study designs have limited statistical power. The mechanism of the vibration effect on bone tissue is likely to be mechanical coupling between an oscillating cell nucleus and the cytoskeleton. More robust dose-response human data are required before therapeutic guidelines can be developed.

Assessment of smoking for low bone mineral density in postmenopausal Turkish women

OBJECTIVE

To investigate the effect of cigarette smoking on bone mineral density (BMD) in postmenopausal Turkish women.

STUDY DESIGN

A total of 175 postmenopausal Turkish women admitted to Tepecik Training and Research Hospital for a routine menopausal checkup were included in this study. All participants completed a questionnaire regarding their age, educational status, parity, number of abortus, time since menopause, caffeine intake, tobacco use, alcohol consumption, history of a previous fracture related to trauma, and taking any medication for menopause and osteoporosis. Of all subjects, 23.3% (n = 39) were smokers and 77.7% (n = 136) were nonsmokers. T-scores and Z-scores of vertebra and femur neck were assessed using dual energy X-ray absorptiometry (DXA). For analyzing the results, Student t-test, one-way ANOVA, Mann-Whitney U test, Pearson correlation, and Kruskal-Wallis test were performed.

RESULTS

Femur T-scores (- 0.78 ± 1.07 vs. - 0.32 ± 1.56) and vertebra T-scores (- 2.26 ± 1.23 vs. - 1.82 ± 1.04) were significantly lower in smoking women than nonsmoking women (p < 0.05). However, there were no significant difference between duration of smoking, number of cigarettes consumed per day, and BMD (p > 0.05) CONCLUSION: Cigarette smoking is one of the modifiable risk factors influencing bone density in postmenopausal Turkish women. "Cessation of cigarette" should be recommended for lifestyle modifications to prevent postmenopausal osteoporosis.

Bone mineral density and general health of long-term residential psychiatric inpatients

OBJECTIVE

The aim of this study was to determine the rates of osteopenia and osteoporosis and other general health problems in a long-stay male psychiatric unit.

METHOD

All 15 patients underwent a semi-structured clinical interview and a full physical examination including calculation of Body Mass Index, central obesity (abdominal circumference) and blood pressure measurement. All patients had blood sampling examining FBC, U&E, LFTs, TFTs, PSA, prolactin, lipid profile and glucose. The rates of metabolic syndrome were calculated according to the International Diabetes Federation consensus worldwide definition. Bone mineral density was determined in the lumbar vertebrae and left hip by DEXA scanning.

RESULTS

The prevalence of osteopenia or osteoporosis was 46%, and bone mineral density was inversely correlated with serum prolactin levels (r = -0.595, p = 0.041) and chlorpromazine equivalence (r = -0.645, p = 0.017). The prevalence of obesity was 53%, while central obesity was present in 87% of patients. Metabolic Syndrome was present in 27% of patients.

CONCLUSIONS

More attention should be given to diagnosing and treating osteopenia and osteoporosis in patients on long-term antipsychotic agents and preventative measures should form part of any treatment regime in these individuals. Frequent input from dietitians should also be available for long-stay psychiatric inpatients to reduce the prevalence of obesity.

Body composition in heavy smokers: comparison of segmental bioelectrical impedance analysis and dual-energy X-ray absorptiometry

Smokers tend to have lower body mass index, on one hand, and increased abdominal obesity, on the other hand. Also, low levels of lean mass (LM) and bone mineral content (BMC) were found among older smokers compared with non-smokers. This altered body composition and its consequences raise the need for simple and reliable methods for assessment of body composition in smokers. This study aimed to compare body composition assessment by segmental bioelectrical impedance analysis (sBIA) with the reference method, dual energy X-ray absorptiometry (DEXA). Body composition was measured by sBIA (Tanita BC-545) and DEXA (Hologic) in 49 heavy smokers (>15 cigarettes/day, mean age 43.8±12.0). The comparison included correlations and differences between measurements obtained using the two methods as well as the Blande-Altman analysis. Whole-body fat mass (FM) and LM measured by the two methods were found to be highly correlated (r>0.9, p<0.001). Compared with DEXA, sBIA significantly overestimated whole-body LM and BMC (1,126 g and 382 g, respectively, p<0.01). The Bland-Altman analysis revealed a good agreement for whole-body FM and LM, but a poor agreement for BMC. The segmental FM percentage and LM were also highly correlated (r>0.9, p<0.001). However, sBIA significantly overestimated LM of the trunk and legs and underestimated the appendicular FM percentage. Verified by DEXA, sBIA provides reliable measures of whole-body LM, FM, and trunk FM in heavy smokers. A lesser degree of agreement was found for BMC, appendicular LM, and FM.

A closer examination of the interaction among risk factors for low back pain

PURPOSE

To evaluate the interactions of risk factors and identify their most powerful discrimination pathway for the occurrence of low back pain (LBP).

DESIGN

A cross-sectional study.

SETTING

Taiwan.

SUBJECTS

Taiwanese population of 30 to 64 years old.

MEASURES

A self-reported question, "Have you experienced LBP within the last 3 months?" was used to evaluate LBP. The study variables included demographics (age, gender, occupation, education level, marital status, and household income), biometric health measures (bone mineral density and body mass index), dietary habits (weekly milk, coffee, tea, and soybean consumption), and other lifestyle factors (smoking habits, alcohol consumption, betel nut chewing, body weight control, exercise regularity, and stress management).

ANALYSIS

Logistic regression and classification tree analyses.

RESULTS

A total of 969 Taiwanese participants were analyzed. Primary logistic regression analysis identified three critical risk factors (gender, bone mineral density, and exercise regularity) for the occurrence of LBP. By classification tree analysis, demographic factors, dietary habits, and lifestyle factors had modifying effects on LBP.

CONCLUSIONS

Various factors contribute to the risk of LBP. Interactions between risk factors should be considered when developing future strategies for the prevention and management of LBP.

Risk factors of osteoporosis in healthy Moroccan men

Background

Although not as common as in women, osteoporosis remains a significant health care problem in men. Data concerning risk factors of osteoporosis are lacking for the male Moroccan population. The objective of the study was to identify some determinants associated to low bone mineral density in Moroccan men.

Methods

a sample of 592 healthy men aged 20-79 years was recruited from the area of Rabat, the capital of Morocco. Measurements were taken at the lumbar spine and proximal femurs using DXA (Lunar Prodigy Vision, GE). Biometrical, clinical, and lifestyle determinants were collected. Univariate, multivariate, and logistic regression analyses were performed.

Results

the mean (SD) age of the patients was 49 (17.2) years old. The prevalence of osteoporosis and osteopenia were 8.7% and 52.8%, respectively. Lumbar spine and hip BMD correlated significantly with age, weight and BMI. When comparing the subjects according to the WHO classification, significant differences were revealed between the three groups of subjects for age, weight and BMI, prevalence of low calcium intake and low physical activity. The multiple regression analysis found that only age, BMI, and high coffee consumption were independently associated to the osteoporotic status.

Conclusion

ageing and low BMI are the main risk factors associated with osteoporosis in Moroccan men.

Coffee consumption and CYP1A2 genotype in relation to bone mineral density of the proximal femur in elderly men and women: a cohort study

Background

Drinking coffee has been linked to reduced calcium conservation, but it is less clear whether it leads to sustained bone mineral loss and if individual predisposition for caffeine metabolism might be important in this context. Therefore, the relation between consumption of coffee and bone mineral density (BMD) at the proximal femur in men and women was studied, taking into account, for the first time, genotypes for cytochrome P450 1A2 (CYP1A2) associated with metabolism of caffeine.

Methods

Dietary intakes of 359 men and 358 women (aged 72 years), participants of the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS), were assessed by a 7-day food diary. Two years later, BMD for total proximal femur, femoral neck and trochanteric regions of the proximal femur were measured by Dual-energy X-ray absorptiometry (DXA). Genotypes of CYP1A2 were determined. Adjusted means of BMD for each category of coffee consumption were calculated.

Results

Men consuming 4 cups of coffee or more per day had 4% lower BMD at the proximal femur (p = 0.04) compared with low or non-consumers of coffee. This difference was not observed in women. In high consumers of coffee, those with rapid metabolism of caffeine (C/C genotype) had lower BMD at the femoral neck (p = 0.01) and at the trochanter (p = 0.03) than slow metabolizers (T/T and C/T genotypes). Calcium intake did not modify the relation between coffee and BMD.

Conclusion

High consumption of coffee seems to contribute to a reduction in BMD of the proximal femur in elderly men, but not in women. BMD was lower in high consumers of coffee with rapid metabolism of caffeine, suggesting that rapid metabolizers of caffeine may constitute a risk group for bone loss induced by coffee.

Opinions and attitudes concerning osteoporosis among Austrian general practitioners

General practitioners play a crucial role in the management of osteoporosis. Thus, it is essential to determine the opinions and attitudes of family doctors concerning this disease. A structured pencil-paper questionnaire was distributed to all general physicians in a practice in Austria and 3.2% responded. Results were compared with a similar survey carried out in 1993. 84.4% of the responding doctors regarded the public health impact of osteoporosis as rather or very important, compared with 49.2% in 1993. 83.3% regarded prevention of osteoporosis as effective or very effective. This proportion rose from 66.2% in 1993. Regular physical exercise was rated as most effective in the prevention of osteoporosis, followed by calcium-rich diet and vitamin D- and calcium supplementation. 33.6% reported carrying out a standardised risk assessment prior to referral/non-referral for bone mineral densitometry. The most frequently cited aspects of the patient's medical history leading to this examination were permanent corticosteroid therapy, a history of fractures, and pain, as reported by 93.6, 84.6 and 71.2%, respectively. The most frequently reported interventions recommended by doctors to their osteoporosis patients in the prevention of falls were reduction of trip hazards (87.2%), reduction of psychotropic drugs (50.0%), balance, strength and endurance training (57.7, 48.1, and 42.3%, respectively). These results reveal strengths in the approach to prevention and early recognition of osteoporosis and prevention of falls, but potential room for improvement in the management of osteoporosis by general practitioners is also shown.

Determinants of bone mass and bone size in a large cohort of physically active young adult men

The determinants of bone mineral density (BMD) at multiple sites were examined in a fit college population. Subjects were 755 males (mean age = 18.7 years) entering the United States Military Academy. A questionnaire assessed exercise frequency and milk, caffeine, and alcohol consumption and tobacco use. Academy staff measured height, weight, and fitness. Calcaneal BMD was measured by peripheral dual-energy x-ray absorptiometry (pDXA). Peripheral-quantitative computed tomography (pQCT) was used to measure tibial mineral content, circumference and cortical thickness. Spine and hip BMD were measured by DXA in a subset (n = 159). Mean BMD at all sites was approximately one standard deviation above young normal (p < 0.05). African Americans had significantly higher hip, spine and heel BMD and greater tibial mineral content and cortical thickness than Caucasians and Asians. In Caucasians (n = 653), weight was a significant determinant of BMD at every skeletal site. Prior exercise levels and milk intake positively related to bone density and size, while caffeine had a negative impact. There was an apparent interaction between milk and exercise in BMD at the heel, spine, hip and tibial mineral content and cortical thickness. Our data confirm the importance of race, body size, milk intake and duration of weekly exercise as determinants of BMD and bone size.