Submariners are exposed to both psychological and physical stresses during a patrol. They are separated from their families and confined to a limited area. The length of their day is shortened from 24 to 18 hours. This routine—coupled with increasing vitamin deficiencies as the patrol progresses—results in lowered morale and decreased work efficiency.
The separation from family members and confinement are difficult to offset. Nevertheless, vitamin supplements would increase work output, because vitamin deficiencies have been reported during submarine patrols. Specifically, Vitamins C and B-6 levels decrease during prolonged patrols because of a lack of fruits and vegetables. Vitamin D levels also decrease significantly, because there is little or no exposure to natural sunlight during a patrol. In adults, prolonged deprivation of Vitamin D can lead to osteomalacia, softening of the bone.
Submarines are typically lighted by standard fluorescent tubes, which emit very little of the ultraviolet radiation essential for Vitamin D synthesis in the skin. This lack of ultraviolet exposure is further complicated by dietary changes. After 30 days at sea, fresh fruits and vegetables are no longer available, and fresh dairy products are replaced by powdered substitutes.
In one study, Vitamin D levels were measured in 22 submariners before, during, and after a two-month patrol. Eleven subjects received a multivitamin-mineral supplement, and the remaining 11 received a placebo. Figure 1 represents the data for each time interval for each group. The placebo group showed a 38% drop in circulating Vitamin D at the mid-patrol point and a 40% drop by the end of the patrol. The supplemented group showed a 17% decrease in blood levels at mid-patrol and a decrease of 3% at the end of the patrol. In the nonsupplemented group, all 11 subjects showed a decline in Vitamin D levels from the pre-patrol to the mid-patrol measure, and 10 of the 11 from pre-patrol to the end of the patrol. Conversely, in the supplemented group, 8 of the 11 subjects showed a slight decrease at mid-patrol, and only 5 showed a gradual decline over the full patrol. The differences between the two groups were significant. The sudden jump at the post-patrol phase was caused by an overcompensation of the body to regain lost Vitamin D by dietary and ultraviolet means.
Vitamin D is also required for calcium absorption in the intestine. As a result of recent studies, the characteristic decreasing levels of Vitamin D explain a 50% decrease in urine calcium excretion, as seen in patrols and several weeks into the post-patrol or recovery period. The 'll effects from retained calcium include calcifications of the kidneys— kidney stones.
The overall health of nuclear submariners is not affected by the submarine environment, but studies like these have identified specific groups at risk—such as older males, for whom some kind of supplementation is needed. A vitamin supplement for submariners should be provided, both for health and for enhancement of performance in environments that lack sunlight.
Another problem faced by nuclear submariners is a significant drop in activity levels while underway. Decreased activity in submariners not only reduces overall Productivity but also results in defective carbohydrate metabolism. In one study, insulin and glucose values were measured in 58 submariners with five or more Patrols, and also 58 non-submariners. A relationship between serum glucose and insulin for classifying defects in carbohydrate metabolism is indicated, because 55% of the submariners exhibited some type of defect.
Exercise appears to play an important role in the maintenance of normal carbohydrate metabolism in these subjects. Non-submariners reported engaging in significantly more exercise than submariners. An inverse relationship was observed between amount of exercise and the severity of carbohydrate metabolic defects in the subjects. There was no significant difference between submariners and non-submariners with regard to glycosylated hemoglobin or fasting glucose. However, notably higher serum glucose levels occurred one and two hours following the glucose load in the submariners. The submariners also exhibited a profound delay in the return of insulin levels at two hours after the glucose load.
The study indicated that when the number of subjects with normal carbohydrate metabolism and the total number of those with carbohydrate defects are compared, 55% of the submariners exhibited defects, in contrast to 45% of the controls. The conclusions are that submariners possess a shift toward glucose intolerance, resulting from increased peripheral insulin resistance and, therefore, a tendency toward the development of defective carbohydrate metabolism. This increase in insulin resistance results more from decreased exercise among submariners than from increased carbohydrate intolerance associated with obesity, since the submariners were found to be no fatter than the controls.
Another study of submariners quantified an observed drop in physical conditioning. The activity levels of 44 submariners were monitored before and during a fleet ballistic missile submarine patrol. These levels were determined by use of a pedometer worn on the hip. Readings were obtained daily and recorded as miles walked. This reduction of more than 50% in activity is responsible for the physical deconditioning observed during the course of a 40 to 70- day submergence period.
Increased physical fitness will produce a more vigilant and productive worker. Exercise regimens on board submarines will reduce weight fluctuations and promote the reduction of the development of defective patterns of carbohydrate metabolism in submarine personnel. A combined vitamin supplement and exercise regimen would result in more healthy and fit submariners and, consequently, a more productive and efficient work force.
Ensign Hardee graduated from the U.S. Naval Academy in May. He will report to Nuclear Power School, Orlando, Florida, in July.