Effect of a 68-day submarine patrol on serum 25-hydroxyvitamin D levels in healthy men.

Serum 25-OH-D levels were determined for 30 submariners prior to, and near the end (day 63), of a patrol lasting 68 d. A significant reduction occurred in serum 25-OH-D levels during the patrol compared to levels obtained before the patrol. Nearly one-third of the sample has serum 25-OH-D levels that were below the minimum normal levels. The late-patrol depletion of serum 25-OH-D was not associated with lower levels of calcium. On the contrary, serum calcium levels were found to be significantly elevated during the late-patrol period compared to pre-patrol levels, even among those submariners who had serum 25-OH-D levels in the low normal or below normal range. This calcium effect may be mediated by the high levels of carbon dioxide maintained in the submarine breathing atmosphere.