Risk Factors for Osteoporosis: Prevalence, Change, and Association With Bone Density

Janet R. Guthrie, MSc, Dip Ed, PhD, Peter R. Ebeling, MB BS, MD, FRACP, Lorraine Dennerstein, AO, MB BS, PhD, FRANZP, DPM, John D. Wark, MB BS, PhD, FRACP

Disclosures
In This Article

Discussion

Risk factors for osteoporosis, which can be relatively accurately quantified, were prevalent in our cohort of midlife women. The following single risk factors were reported by, or measured in, over 20% of the cohort: low peak bone mass, low calcium, low physical activity levels, a family history of osteoporosis, high caffeine intake, and past smoking habits. Low BMI, high alcohol intake, and a history of menstrual disturbances were reported by 10% or less of the cohort. The use of prescription drugs likely to affect bone metabolism was minimal. The simultaneous occurrence of risk factors within 1 individual has important risk implications because of possible additive effects and interaction between factors. When the risk factors of low calcium and low physical activity are considered, 13% of the cohort have both these risk factors.

There is no literature on the prevalence of all these risk factors for osteoporosis in a similar-aged population sample of Australian-born women with which to compare our results. Table 4 lists various risk factors as measured in Finnish and American population studies and in the follow-up measures of our cohort.

In these 3 Caucasian populations, there are differences in the reporting of current smoking, physical activity, calcium intake, and HRT use. It will be interesting to compare the osteoporotic fracture outcomes within and between these populations in another 10-20 years. This will provide some information on the importance of various risk factors and their roles in the development of osteoporosis.

Rates of osteoporotic fracture vary greatly by country[16] and in different racial groups within countries. Whether these variations result from the prevalence of different risk factors or other unexplained variables is yet to be satisfactorily determined.

We combined the pre- and early perimenopausal women into 1 group to provide greater power for analysis of the association of BMD with risk factors. Previous analyses have shown no significant differences between these groups with regard to hormone levels,[17] menopausal symptoms,[18] and bone changes.[19] Weight, height, and measures of body fatness were all significantly positively associated with BMD at both the LS and FN, confirming associations that had been shown in a smaller cohort of Australian-born women.[20] The significant negative association between age and FN-BMD but not LS-BMD also confirms our earlier studies in a smaller cohort[20] and the work of other investigators.[21]

There was a change in weight and fat distribution during the study period. Weight gain in this cohort has been shown not to be related to the menopause per se,[7] although changes in fat distribution were associated with the menopausal transition. These changes may be beneficial for bone health but not for cardiovascular health.[22] Changes in lifestyle risk factors were in the direction that would decrease rather than increase the risk of osteoporosis. There was a reduction in caffeine intake, an increase in calcium intake, and no significant changes in physical activity and smoking. Of note is that the women who were assessed in this study were provided with results of their BMD measurements. The fact that women were involved in a longitudinal study of BMD may have made them more aware of their lifestyle, and the improvement, particularly in calcium intake, may have ensued.

The pattern of bone loss in the LS and FN during the menopausal transition is similar to that reported previously.[19] These earlier results were over an approximate 2-year span and showed a greater loss per year than over the 4-year period (2.5% vs 1.8% at the LS and 1.7% vs 1.0% at the FN), highlighting the accelerated bone loss that occurs just after the FMP. The inverse relationship between bone loss at the FN and baseline FN-BMD in women who experienced the menopausal transition has been reported in other studies,[23,24,25] and there was no influence on bone loss by lifestyle or gynecologic variables, as has been reported previously.[19]

The differences in the patterns of bone loss in the LS and FN in the early postmenopausal period probably reflect the differences in bone structure of these sites. Trabecular bone is reported to compose 50% to 60% of the bone mass of the LS[26] and 25% of the bone mass of the FN.[27] Bone remodeling is more active in trabecular bone, probably because of its high surface-to-volume ratio; as a result, trabecular bone mass changes more quickly in response to negative influences such as estrogen deprivation.[28]

Some limitations of this study are that the ranges and levels of both calcium intake and physical activity were not sufficient to override the effect of ovarian changes on bone metabolism. On the basis of data from calcium balance studies, Heaney and colleagues[29] recommended a calcium intake of 1600 mg/day for estrogen-deprived women, more than was consumed by the majority of our cohort. The intake was less than 900 mg/day for approximately half of our cohort, a lower estimate of calcium requirement derived from the calcium balance studies of Nordin.[30] The physical activity profile of the cohort was not at the level of resistance training that has been shown in intervention studies to improve bone mass in postmenopausal women.[31,32]

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