Little data are available regarding risk factors for fracture and low bone density among Chinese American women. Chinese American women represent a growing population at risk for osteoporosis. By the year 2050, one-tenth of the US population will be of Asian descent, many of them Chinese American, according to the United States Census Bureau.50 In a cross-sectional study, we investigated predictors of BMD in 359 ambulatory Chinese American women, ages 20–90, using stepwise multiple regression analysis.46 Variables in the model included age, weight, height, menarche age, years since menopause, immigration age, years in the US, percentage of life in the US, number of pregnancies, oral contraceptive use, family history of osteoporosis, daily calcium intake, exercise, time outdoors, alcohol consumption and tobacco use. Among premenopausal women, weight was the most robust predictor of BMD, accounting for 10.5% of the variance at the lumbar spine (LS), 15.2% at the total hip (TH) and 16.6% at the femoral neck (FN). Time outdoors was also a positive predictor of BMD (1.4% at LS, 2.8% at TH, 1.6% at FN), while family history of osteoporosis (1.4% at TH) and age (3.7% at FN) were negative predictors. Among postmenopausal women, greater BMD at the LS and TH was associated with greater weight and earlier immigration age. Weight explained 16.4% of the variance at the LS and 19.8% at the TH; immigration age accounted for 3.1% of the variance at the LS and 4.1% at the TH. At the FN, years since menopause and weight were predictors of BMD, accounting for 14.4% and 8.7% of the variance, respectively.
As in other racial groups weight is the major predictor of BMD in Chinese American women. Limited nutritional information was collected, but calcium intake was not an independent determinant of BMD in this study. However, calcium intake was low [612 ± 17 mg (mean ± SD) daily]. Among premenopausal women, time outdoors was a significant predictor of BMD. This variable may reflect vitamin D status, physical activity or general health. Among postmenopausal women, older age of immigration to the US, independent of weight or age, had a negative effect on BMD. We hypothesize that later age of immigration may have a negative effect on BMD because51 older individuals are less likely to take on a Western lifestyle when they do immigrate or1 individuals who emigrate past a certain age may not be able to significantly alter BMD with lifestyle changes. More data are needed to differentiate between these possibilities. Bone mineral density in Chinese American women is influenced by a number of biological and lifestyle factors, including immigration. The results of this study provide new insights into risk factors for low bone density as they relate to environmental determinants in the growing population of Chinese American women.
In summary, racial differences in BMD are influenced predominantly by weight and bone size. Differences in African Americans persist even with adjustment for these factors. Racial differences in fracture rates are not completely explained by differences in areal BMD. The relationship between BMD and fracture risk may be altered by racial differences in bone size, hip axis length (hip fracture), other bone qualities or non-skeletal factors. More data are needed to provide screening and treatment recommendations that are relevant for non-Caucasian individuals.