The relationship between calcium, vitamin D status, anthropometry, physical activity and bone density in Black men : a case control study

Abstract

Osteoporosis literally means 'porous bone" and is characterized by an increase in bone fragility and susceptibility to fracture, which typically involves the wrist, spine and hip (South African Medical Association (SAMA) Working Group, 2000). In South Africa osteoporosis and fractures are more common in whites than in blacks. African-American men experience hip fractures at a rate of only half of that of Caucasian men. The bone mass in Africans were found to be 6 - 12 % higher than in Caucasians at all ages. A higher peak bone density at skeletal maturity in African-Americans were found, so that despite comparable age related bone loss, African Americans reach the fracture threshold less frequently than whites. Age-related bone loss that begins later, is less severe, or occurs in different skeletal sites in African-Americans than whites (Luckey et al., 1996). American whites have a higher bone turnover than American blacks, but in contrast to this American data. South African blacks may have a higher bone turnover and lower bone density than whites (Daniels et a/., 1995). If it is compared with Caucasians a lower rate of hip fracture in South African blacks were found, despite lower bone density at all ages (Villa, 1994). The lower fracture rate in blacks than in whites is because of greater bone mass and higher bone turnover leading to more frequent renewal of damaged bone. Blacks excrete less urinary calcium, and show no skeletal sensitivity towards the parathyroid hormone. Few studies focus on older black South African men and osteoporosis. Objectives: The aim of this study was to investigate the relationship of calcium intake, vitamin D status, anthropometry and physical activity and bone density in black South African men. Methods: A case-control study design was used, in which variables associated with bone density were compared. The case group were men with fractures of the proximal femur, the proximal humerus or the distal radius and an equal number of age-matched healthy black men (with not more than a 5-year age difference) with no fracture (the proximal femur and humerus and distal radius) previously, was recruited as a control group. Bone density was measured with DEXA. Fat percentage was measured with a Tanita scale. Biochemical analyses were done. Questionnaires were used to gather demographic, activity and dietary information. To our knowledge, this is the first case-control study on osteoporotic fractures in South African black men. Results: Both the groups' bone mineral densities were lower than recommended. The bone density of the case group for lumbar and hip regions was 0.86 and 0.88 and the control group's bone density for lumbar region was 0.95 and hip region 0.91. The control group was more physically active and had a better nutritional status than the case group. The control group's calcium intake was higher but the vitamin D status was lower than the case group. Both calcium and vitamin D status were not statistically significant (pc0.5), between the two groups. Body mass indices of the groups were the same. The serum albumin was higher in the control group than in the case group. The case group serum calcium was higher than the control group. Both serum albumin and serum calcium were statistical significant between the two groups. There were no statistically significant differences in any of the other biochemical variables between the two groups. Serum phosphate and serum vitamin D were statistical significant for bone density of the hip and lumbar regions. Conclusion: To conclude it seems logical to suggest a healthy diet with optimal macro- and micro nutrient intake. Maintain ideal body weight and body fat percentage and recommend regular but moderate-weight-bearing exercise from a young age throughout adult life, as part of a strategy to prevent and treat osteoporosis. In the present study black South African men present with low bone mineral density, but other studies indicated a lower rate of hip fracture in South African blacks, despite lower bone density at all ages. It can be recommended that other factors may play a role in black South African men with osteoporosis. Factors such as serum phosphorus, 25-hydroxy-vitamin D, body mass index (BMI), physical activity index (PAI), animal protein, total fat intake and dietary calcium are important determinants of BMD in older South African blacks, as shown in the present study. Osteoporosis is a multi factorial problem and must be treated that way.