Dietary calcium intake, physical activity and the risk of vertebral fracture in Chinese.

To study the relationship between dietary calcium intake, load-bearing activity, reproductive factors, anthropometric factors and vertebral fracture in Chinese, a case-control study was carried out on 481 women (aged 70-79 years) who lived in three housing blocks under the Geriatric Priority Housing Scheme in Shatin, Hong Kong. Lateral spine radiographs were taken from the T4 to L4 level. Definite and doubtful vertebral fractures were diagnosed when any of the three vertebral height (anterior to anterior, middle to posterior and posterior to posterior) ratios was 3 SD and 2-2.99 SD below the mean respectively. Women with one or more definite fractures were classified as definite cases, those with one or more doubtful fractures were classified as doubtful cases, and the rest as controls. The mean dietary calcium intake and load-bearing activities were obtained by interview, using a structured questionnaire. Detailed information on cigarette smoking, alcohol consumption and reproductive factors was also obtained. The grip strength, body weight and height were measured. Doubtful cases were found to differ little from the controls in their lifestyle and anthropometric factors. The odds ratio (OR) for being a definite case was 2.1 (95% CI = 1.1-3.9) when the dietary calcium intake was in the lowest quartile. The OR was 1.8 (95% CI = 0.8-4.4) for subjects who walked or exercised outdoors for less than an hour a day. Giving birth to or breast-feeding three children or more was protective against definite fracture. The definite cases were significantly lighter and shorter than controls; they also had a weaker grip strength. It is concluded that a low dietary calcium intake was significantly associated with an elevated risk of vertebral fracture, while the effect of infrequent load-bearing activity was uncertain. Giving birth to or breast-feeding three or more children was protective against vertebral fracture in our population.