Risk factors for osteoporotic fractures in Black South African men : a case control study

Abstract

The main focus of bone loss and Osteoporosis (OP) research has been limited almost entirely to women, but OP has become increasingly common in older men and the impact of hip fracture on mortality may actually be greater in men. OP is a major cause of morbidity and mortality in developed countries, at a cost that currently exceeds $10 billion per year in the United States (US) alone. Osteoporotic fractures affect 50 % of women and 20-30% of white men and 4% of black men over the age of 50 years. These statistics may even increase because of increasing life expectancy. Few studies focusing on Blacks have been published to date and very little is known regarding the bone health and the aetiology and prevalence of OP and fractures among older South African blacks. From the above information it is clear that OP is of considerable clinical and economic importance. Without information on the patterns and determinants of bone loss, the formulation of rational prevention and treatment strategies in these groups is not possible. The aim of the study described in this thesis was to investigate the influence of the dietary factors (iron, vitamin C, and protein) and lifestyle factors (alcohol and tobacco smoking) on osteoporotic fractures and bone mineral density in older South African black men using a case-control study design. Sixteen black male patients with fractures of the proximal femur, the proximal humerus or the distal radius and who conformed to the inclusion and exclusion criteria were included in the study. An equal amount of age-matched (±2 years), apparently healthy black men with no previous fracture (of the proximal femur and humerus and distal radius), were recruited as a control group. Dual energy X-ray absorptiometry (DEXA) was used for the measurement of the lumbar vertebrae and the proximal femur (hip). Questionnaires were used to gather demographic and medical information, data on physical activity and dietary intakes. Anthropometric measurements and blood samples were taken. Appropriate biochemical analyses were done with standard methods. Both the cases and controls were osteoporotic according to the mean lumbar spine BMD determined in both groups. The BMD was only marginally lower in the cases than in the controls and therefore not statistically significant. The mean tobacco pack years of the cases (13.29) [95% CI: 4.44; 22.141 were almost double that of the controls (7.43) [1.83; 13.031 but it was not statistically significant (p=0.55). Tobacco pack years were negatively associated with BMD of the lumbar spine (p=0.008) even after controlling for possible confounding factors (p=0.001). Malnutrition, as indicated by the low dietary intakes of energy, protein, vitamin C, iron and low BMI, could play a role in the lower bone mineral density (BMD) observed in the cases. The mean protein intakes of the cases (56.1 19) [46.49; 65.741 were very low compared to the recommended 639 per day. This low protein intake was also significantly less compared to the controls (739) [58.28; 88.311. lron intake tended to be lower in the cases compared to the controls (p=0.09). lron intake was not associated with BMD, however, in the stepwise regression analysis; iron intake came out as a possible predictor of BMD of both the lumbar spine and hip, although it was not statistically significant. The BMI was c 19 kg/m2 in 50% of the cases and the controls. S-GGT, a marker of alcohol intake, was significantly increased in the cases with a mean value of 65.88ulL opposed to the 36.33UIL in the control group. S-GGT was the most important predictor of BMD in both the hip and the lumbar spine. There was a significant statistical correlation between lumbar spine BMD (p=0.04); hip BMD (p=0.02) and s-GGT. In conclusion it can be said that malnutrition played a vital role in the low BMD aggravated by the use of tobacco from a young age and alcohol in excessive amounts over weekends. From the results of this study it can be recommended that any intervention programme should focus on alcohol abuse, tobacco smoking and improvement in nutritional status. Children should be encouraged not to smoke and be educated on the detrimental effects of alcohol. It is important to address dietary risk factors associated with OP, namely to increase the overall nutrition of the South African black male with low cost protein and calcium products. Vitamin C enhances iron absorption and may be beneficial for bone collagen. The increased intake thereof by using seasonal fruit can therefore be recommended.