Determinants of bone mineral density in middle aged men: a population-based study

Osteoporosis is a growing health problem not only in women but also in men. To assess determinants of bone mineral density (BMD) at the spine and proximal femur, a randomly selected sample of 140 Finnish men aged 54-63 years was measured using fan beam dual-energy X-ray absorptiometry. Isometric muscle strength was measured using a computerized measurement system and cardiorespiratory fitness was assessed with maximal oxygen uptake (VO2 max) using breath-by-breath respiratory gas analyses during an incremental bicycle ergometer exercise. Intakes of calcium and energy were estimated using 4-day food records. Smoking habits and alcohol consumption were assessed from an interview and a 4 week diary, respectively. Isometric muscle strength of triceps and biceps brachii, extensors and flexors of thigh and rectus abdominis correlated significantly with BMD (r = 0.18-0.35, p = 0.02-0.000). Calcium intake correlated positively with femoral (r = 0.19-0.28, p = 0.03-0.003), but not with lumbar BMD. In addition, calcium intake adjusted for dietary energy content (mg/MJ) correlated with femoral BMD (r = 0.25-0.36, p = 0.03-0.000). Smoking had no effect on BMD, whereas alcohol intake correlated positively with BMD at L2-L4 (r=0.19, p = 0.031). In the multiple linear regression analysis adjusted calcium intake predicted BMD in every site measured, while strength of abdominal muscles predicted BMD at Ward's triangle and femoral neck. Body weight was a predictor of trochanteric BMD. Body height was the best predictor of lumbar and femoral neck area. We conclude that low dietary calcium intake, weak muscle strength and low body weight are risk factors for low BMD in men.