Caffeine, urinary calcium, calcium metabolism and bone.

Oral doses of caffeine increase the urinary excretion of calcium, magnesium, sodium and chloride for at least 3 h after consumption. The hypercalciuric effect can be blocked by adenosine receptor agonists. The effect is proportional to dose per lean body mass and no adaptation to the urinary losses occurs with continuing consumption of caffeine. Uncompensated losses of calcium would be a risk factor for development of osteoporosis. Risks of osteoporosis due to caffeine consumption are reviewed. Comparison of data from epidemiological surveys and animal and human studies suggests that for younger adult women consuming adequate calcium, moderate caffeine intakes may have little or no deleterious effects. Increased urinary and intestinal losses may be compensated for by increased intestinal calcium absorption. However older women do not seem to compensate adequately to maintain their former calcium balance, especially when calcium intakes are below recommendations.