Abstract: BACKGROUND: Studies have demonstrated that postmenopausal osteoporosis is related to female reproductive characteristics and exercise diets, but few studies have demonstrated whether female reproductive characteristics and exercise diets have an effect on vitamin D in postmenopausal women.
OBJECTIVE: To investigate the relationship of vitamin D levels with female reproductive characteristics and exercise diets and their influencing factors in postmenopausal women in Beijing.
METHODS: Totally 727 postmenopausal women with an age range of 46-75 years old who received on-site questionnaires in 17 communities of Beijing from September 2017 to May 2018 were selected as the study subjects, and the questionnaires included the subjects’ basic information and history of menstruation, menopause, pregnancy, and exercise diet. An electrochemiluminescence immunoassay analyzer and its auxiliary reagents were used to determine 25-(OH)D levels. Bone mineral density and T values of the lumbar spine (L1-L4, whole) and both hips (femoral neck, whole) were determined using a dual-energy X-ray bone mineral density detector. The correlation of vitamin D with reproductive characteristics and exercise diet was observed, as well as the influencing factors of vitamin D were analyzed. 
RESULTS AND CONCLUSION: There were 136 cases (18.7%) in the vitamin D normal group, 389 cases (53.5%) in the vitamin D insufficient group, and 202 cases (27.8%) in the vitamin D deficient group. The mean vitamin D level was (15.60±5.85) ng/mL. With the increase of vitamin D level, the bone mineral density value and T value of different parts of the body also increased. Vitamin D level was positively correlated with age at menarche, days of menstrual duration, stage of menopause, activity, diet type, and dietary preference (P < 0.05); was negatively correlated with menstrual cycle, age at menopause, and number of childbearing (P < 0.05); and had no correlation with age at first conception and number of pregnancies (P > 0.05). The results of multifactorial ordered Logistic regression analyses showed that there was a positive correlation between the frequency of drinking dairy products and vitamin D level (P < 0.05), and dairy products were a protective factor for vitamin D level. To conclude, vitamin D levels are generally insufficient and bone mineral density values are generally low in postmenopausal women in Beijing. Vitamin D levels are correlated with some reproductive characteristics and exercise diets, and drinking dairy products is a protective factor. Therefore, it is possible to intervene in the dietary situation of postmenopausal women by means of health education about osteoporosis and by increasing vitamin D levels in order to increase bone density values and reduce the prevalence of osteoporosis in the postmenopausal period.

Key words: Beijing, postmenopausal women, vitamin D, reproductive characteristics, exercise diet, osteoporosis