Carbon dioxide and vitamin D effects on calcium metabolism in nuclear submariners: a review.

Studies in nuclear submariners show that calcium excretion falls rapidly to 50% of pre-patrol levels during long patrols and remains low for many weeks after return to fresh air. This has previously been attributed to a specific effect of continuous exposure to the inevitably raised ambient CO2 levels, but other environmental factors cannot be ignored, in particular isolation from sunlight, which leads to reduced skin synthesis of vitamin D. The role of vitamin D is examined with reference to measured mean circulating blood levels of 25-hydroxyvitamin D at the beginning and end of a submarine patrol and in human exposure chamber investigations. It is concluded that although CO2 exposure has specific effects on calcium metabolism, causing a considerable reduction in urinary calcium excretion, a state of hypovitaminosis C occurs in long submarine patrols that has effects outweighing those of CO2 toward the end of patrols and afterward. The significance of this effect to submariners' health is discussed.