Sunlight and hypercalciuria.
Urinary calcium and magnesium excretion was measured in two groups of soldiers leaving the temperate climate of the united Kingdom for service in the Persian Gulf. In one group urinary calcium levels and magnesium/calcium ratios were similar, ten days after arrival in the Gulf during the "cold season", to those found in the U.K. The other group went to the Gulf in the "hot season", and calcium excretion rose immediately to levels comparable with those found in the first group after eight months. Mg/Ca ratios fell to levels seen in stonformers, and 2 of 91 soldiers followed up for three years have had urinary calculi. Increased exposure to sunlight seems to be the most likely cause of the hypercalciuria.