Submarine Medical Research Laboratory Submarine Base , Groton , Conn

Plasma vitamin C levels were determined for 28 submariners prior to, during, and after a 68-day patrol. A significant reduction occurred in plasma vitamin C levels during the patrol compared to levels obtained before and after the patrol. These reductions were unrelated to health and performance effects as determined by total dispensary visits, frequency of upper respiratory infections, and training accomplishments. Smokers had significantly lower levels of plasma vitamin C than non-smokers, as did those who .had made several previous patrols. Vitamin supplements did not appear to ameliorate the vitamin C deficiency found among smokers, but did enhance the plasma levels of vitamin C among non-smokers. These findings indicate that dietary or supplemental intake of vitamin C among submariners should be increased, especially among those who smoke or who have made several patrols. v * Althoughvitamin-Gr-was notH.-dentif ied—biochemically—until thi-s-r-eentury,—— the importance of fresh fruits and vegetables containing high levels of vitamin C in the maintenance of health and performance has been recognized for over 400 years. While exploring the New World during the 15th and 16th centuries, entire crews were ravaged by scurvy following prolonged periods at sea without fresh food (1), In 1753, a Scottish physician named James Lind published data showing that consumption of oranges and lemons could cure scurvy among sailors (2). In 1804, the Royal Navy required that sailors consume a daily ration of lemons or limes (hence, the name "limey"). Research over the last 50 years has isolated vitamin C biochemically, and demonstrated that humans are totally dependent on diet as the sole source of Vitamin C because of genetic deficiency in the enzyme that catalyzes the oxidation of L-gluconic acid to L-ascorbic acid (3, 4). Today, fresh fruits and vegetables are available routinely onboard most Navy ships. Some ships, however, do not have regular access to fresh food stores because the mission of these ships requires that they remain undetectable, thereby preventing resupply at sea. These ships are nuclear submarines on deterrent ballistic missile patrols. Despite the historical involvement that navies have had in recognizing the importance of vitamin C in health, little has been done to determine if prolonged submarine patrols results in significant vitamin C depletions. During these patrols, that last from 60 to 75 days, fresh fruits and vegetables are consumed during the first week or two, and are not replenished until the patrol is completed. Vitamin C mediates the health effects described above through regulation of a number of biochemical processes. Through regulation of these processes, vitamin C has been implicated in the frequency and severity of respiratory infections, notably the common cold (5, 6). Collagen synthesis is another important process found to depend heavily on the availability of vitamin C (7-11). Deficiencies of vitamin C result in problems in wound-healing (i.e., failure of wounds to heal or deterioration of previously healed wounds) that have been attributed directly to impaired collagen formation (7, 10, 11). Submariners may therefore be a population at risk for woundhealing problems because, as mentioned above, access to dietary vitamin C is diminished substantially during extended submarine patrols. Research has also shown that smokers have low levels of vitamin C (12, 13). A possible explanation for this effect is that smokers absorb less vitamin C from the gut than non-smokers. These findings indicate that smokers may require twice as much vitamin C intake as non-smokers to maintain.comparable blood level of L-ascorbic acid. These data have not been replicated under field conditions, however, nor has the relationship of this condition to health and performance been determined. The following research will document the plasma vitamin C levels of a typical submarine crew, compare these levels between smokers and nonsmokers, and determine whether or not these levels are related to respiratory infections, wound-healing, overall health and training accomplishments. METHOD Twenty-eight men from a ballistic missile nuclear submarine crew of 155 volunteered to participate. The average age of the men was 25.2 years, with a range of 19 to 36 years. The group consisted of two officers, four midshipmen (officer candidates) and 22 enlisted men. The median number of patrols made by this group was three (ranging from one to seventeen), including the present patrol. The volunteers were in excellent health and did not have a history of major disease. Blood samples were collected two days before submerging (pre-patrol sample), on day 63 of the 68-day patrol (late-patrol sample), and 38 days after returning from patrol (post-patrol sample). Pre-patrol and late-patrol plasma samples were deprotenized and oxidized on the submarine prior to shipment on dry ice for vitamin C determinations. Post-patrol samples were collected and prepared for analysis at the laboratory about five weeks after the submariners had completed the patrol. Plasma specimens were assayed for vitarain C within one week of collection using a modification of the 2,4-dinitrophenylhydrazine method of Roe and Kuether (14). Before each sampling period, the volunteers were asked to complete a questionnaire that asked for information about diet, use of vitamin supplements, cigarette consumption per week, and whether or not they had problems with wounds healing more slowly than normal. Sick call records were maintained during the entire patrol by the hospital corpsman assigned to the ship. The group made an average of 1.42 sick call visits during the patrol (ranging from none to ten visits). These records were analyzed further for sick call visits involving symptoms of respiratory infection (congestion, coughing, sore throat, earache, and so forth). RESULTS Table 1 shows the means and standard errors for plasma vitamin C levels of the twenty-eight submariners two days before the patrol (pre-patrol) on Day 63 of the 68-day patrol (late patrol), and 38 days post-patrol (postpatrol) . A one-way analysis of variance for repeated measures showed that significant differences in plasma vitamin C levels existed across the three test conditions (F = 4.29, df = 2, 81; p <.05). Subsequent t-tests demonstrated that the late patrol vitamin C levels differed significantly from both pre-patrol and post-patrol levels (pre-patrol x late patrol: t = 2.24; p<.05; post-patrol x late patrol: _t = 3.35; p<.01). A significant difference was not found between pre-patrol and post-patrol vitamin C levels (_t ~ 1.57; p >.05). These results indicate that during the late-patrol period, plasma vitamin C levels were significantly lower than during the control (preand post-patrol) periods. From the above data, the 28 submariners were divided into two equal groups—the 14 who had the highest levels and the 14 who had the lowest levels of plasma vitamin C during the late patrol period. The range for the high group was 0.87 to 2.32 mg/dl (M ■ 1.46 mg/dl), while the range for the low group was 0.14 to 0.72 mg/dl (M = 0.43 mg/dl). With only one exception, the levels for the low group were below the minimum normal level of 0.60 mg/dl defined by Nino and Shaw (4). Comparisons were then made between these two groups for wound-healing problems, sick call visits for respiratory infections, overall sick call visits and training performance. From research cited above, a priori predications were made that the low group would have more wound-healing problems and sick call visits, as well as fewer accomplishments, than the high group. Comparisons were made using _t-tests for independent samples or z-tests for proportions. For wound-healing, adjustments were made in group totals because three members of the low group and one member of the high group did not incur wounds (cuts or scratches) during the patrol. With these adjustments, seven members of the high group (53.8%) and two members of the low group (18.2%) reported that wounds took longer than normal to heal. This difference, which was in the unexpected direction, was significant (z = 1.798; p <.05). Overall sick call visits were not found to differ significantly between the two groups. Nine members of the low group (64.3%) and seven members of the high group (50%) made at least one visit to the dispensary for some type of illness of injury during the patrol (z^ = 0.748; p = NS). If only those dispensary visits involving symptoms of respiratory infection were analyzed, six members of the low group and three members of the high group were found to make at least one visit to the dispensary for this purpose. Again, the difference was not significant (z = 1.193; p = NS). Training accomplishments were rated according to difficulty. Completing