| Osteoporosis is a systemic skeletal disease, which characterized by low bone density and microarchitectural deterioration of bone tissue with a consequent increase in bone fragility. The prevalence of osteoporosis increases rapidly worldwide due to aging and changed lifestyles. More than 200 million people are affected by osteoporosis and most of them are Asia. If not taking effective action, half of osteoporotic fractures will occur in Asia by 2050. Women have a three-fold higher probability in experiencing osteoporosis than men because of especial physiological change. Aging and sex hormone deficiency are widely recognized as strong determinants in the development of osteoporosis. In addition, nutrition, physical activity, and other lifestyle patterns are also indicated to play roles in maintaining bone health. The present thesis was designed to identify these risk factors from epidemiological point of view, and tried to give some suggestions about osteoporosis prevention strategies. The contents as list were included in this thesis:Examine the different association of human body composition, such as fat mass (FM), lean mass (LM), and fat distribution with bone mineral density (BMD) in pre- and postmenopausal Chinese women.Examine the ethnic difference in the association of body fat and trunk fat with BMD among Chinese, whites, and black subjects.Examine sleep duration patterns in Chinese women and explore its association with total and regional BMD after potential covariates taking into account.The main findings were summarized as follows:LM was positively associated with BMD both in pre- and postmenopausal Chinese women. Muscle activity exerts strain on nearby bone structure, and thus stimulates the adaptive processes of the bone.Increased FM was significantly associated with total and body regional BMD in postmenopausal women, but not in premenopausal women. One explanation is that greater FM imposes a greater mechanical stress on bone, and in response, bone mass increases to accommodate the greater load. Another explanation is adiposity influence BMD through adipocyte-dependent hormonal factors.During menopausal transient, significant changes will occur in fat distribution. Central fat distribution index, android to gynoid fat ration (AOI), was become greater in postmenopausal women than in premenopausal women. In addition, an android type of fat distribution in postmenopausal women was negatively associated with the BMD of total and major body regions. Visceral adiposity-associated inflammatory markers, such as C-reactive protein, tissue plasminogen activator antigen, and adipokines may exert detrimental influence on bone metabolism.Percent body fat (%BF) and percent trunk fat (%TF) were negatively associated with most regional body BMD. The interactions between %BF,%TF, and ethnicity were found in most regional body BMD among Chinese, white, and black subjects for both men and women. In addition, the ethnic differences between %TF and BMD were observed in more body regions than that between %BF and BMD. With an increase in %BF and %TF, both white and black subjects were more likely to decrease their BMD than Chinese subjects within both sexes.A positive association between sleep duration and BMD exists in women. Compared to those who slept 8 h, women who slept 6 h or less per night had a significantly lower level of total and regional BMD. It is very important to encourage adequate sleep duration, at least more than 6 h per night, in women to curb bone loss.In conclusion, bone health is not only related with some fixed factors, such as age, sex, and ethnicity, but also related with some modified lifestyle factors. In terms of osteoporosis prevention, it seems important for women to persevere in physical activity and enhance muscle strength in their whole lifetime, to decrease central fat accumulation during menopausal transient, and to prolong sleep duration at least 6 h per night. These results of present thesis may lead to the development of better preventive approaches to osteoporosis in women. |
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