Effect of calcium intake vs. other life-style factors on bone mass.

Several life-style factors are known to or have been suggested to interact with calcium metabolism and bone turnover. Immobilization or a sedentary life-style may result in substantial bone loss, and physical exercise may increase bone mass, to different extents in different parts of the skeleton. Excessive training and/or slimming may lead to amenorrhoea, which is in turn complicated by rapid bone loss. While calcium supplementation probably cannot override the negative calcium balance induced by immobilization or amenorrhoea, the calcium requirement may be enhanced during recovery from these states. A high body mass index may to some extent protect against bone loss, particularly in post-menopausal women. Tobacco smoking and high alcohol consumption are probably detrimental to bone mass. Insufficient exposure to daylight and/or insufficient vitamin D intake occur mainly in infants and elderly people, and may impair calcium balance and cause rickets, osteomalacia or osteoporosis. Whether high intake of caffeine, protein, phosphate or fibre is detrimental to the bone mass has not yet been clarified. In many populations smoking and consumption of alcohol or caffeine are negatively correlated with calcium intake, and this exemplifies a source of confounding factors. Increased attention would be paid to important life-style factors during investigations of calcium requirements in different sex and age categories.