Lifestyle risk factors and bone mineral density of urban postmenopausal women in the North West Province

Abstract

Background: Osteoporosis and the resultant fractures are increasing globally, making the disease an emerging public health concern. Over the last few decades osteoporosis has been recognised as a disease with a high incidence in urbanised areas in developing countries, including South Africa (SA). In the past it was believed that black people had greater protection against the development of osteoporosis than Caucasians owing to greater bone mineral densities (BMD). Emerging evidence indicates that black, urban postmenopausal women are at an increased risk for the development of low bone mass, decreased bone formation and bone turnover, as well as increased bone degradation because of inadequate dietary intake, reduced physical activity (PA), and low vitamin D status. The current study will therefore aim to explore the role of diet quality and PA as possible contributing factors to BMD in urban black women from the North West Province (NWP). Methods: For this study, a representative sub-sample of urban black Setswana-speaking women (n=325) was recruited, from the first follow-up in 2010 of the PURE SA-NWP study. Inclusion criteria were women > 45 years, not pregnant or lactating, HIV negative, not menstruating and/or have a follicle stimulating hormone (FSH) level of ≥ 40 IU/L, which resulted in a sample size of 171 women. Habitual PA level was assessed with the use of the modified Baecke questionnaire. A sociodemographic questionnaire including questions on contraception use, number of children, medical history, history of alcohol and tobacco use was completed. Dietary data were obtained through a culturally sensitive validated quantified food frequency questionnaire (QFFQ). Under- and overreporters were identified with the Goldberg cut-off. The Healthy Eating Index (HEI) diet quality score was adapted to explore associations between BMD and diet quality. Femoral neck (FN), total hip and lumbar spine BMD were measured with dual energy x-ray absorptiometry (DXA). Results: The total group had a low level of PA (mean WPA = 2.99); 45.6% reported tobacco use, 56.1% were hypertensive and 25.7% used thiazides. Women ≤60 years had significantly higher BMD at all measured sites (FN BMD = 0.743g/cm2 vs 0.689g/cm2, p = <0.01) compared to women >60 years. Osteoporosis was identified amongst 40.4% of the women. The average dietary calcium intake of the group was inadequate [488(344;633)mg] and the adapted HEI diet quality score were low [2(2;3)]. No associations were found between PA, diet and/or BMD. Multiple regression analysis showed that age, height, postmenopausal status, dietary calcium, vitamin D status, alcohol and tobacco use, as well as waist circumference predicted 32% of the variance in femoral neck BMD (r2 = 0.324, p<0.001). Conclusion: Lifestyle behaviours associated with urbanisation and age-related bone loss increase the risk of osteoporosis in black postmenopausal SA women from the NWP. In order to decrease the incidence of osteoporosis and its associated fractures, prevention strategies should include education on the importance of reduced alcohol and increased calcium intakes in this group of women.