The environment in the Antarctic is quite unique. Seasonal changes in UV-B exposure are more extreme than in any other part of the world. The sun does not rise for 42 days during winter (June 1 – July 12), and the sun does not set for 60 days during the summer months (Nov 22 – Jan 20). During the Antarctic winter, scientists and visitors are typically isolated, and no fresh fruits or vegetables are available. As a result of close quarters and limited food choices throughout the year, most scientists at a particular research station have homogeneous food intakes and physical activities. Not only is Antarctic winter-over a good model for studying vitamin D metabolism because of the limited sunlight exposure, the Antarctic science station model has also been used successfully as a ground-based analog for space flight in studies of behavior, immune response, and latent virus reactivation. Antarctica was used in the proposed study to test the hypothesis that stress causes a reduction in the immune response. The Antarctic winter is similar to space flight with regard to the amount of ultraviolet radiation, which is zero during these months. This is an excellent environment for estimating how effective vitamin D supplements would be in space.
The investigators recently completed a ground-based investigation evaluating vitamin D supplementation efficacy during the winter months in Antarctica, when UV-B radiation levels are zero. A supplement of 2,000 IU/d raised serum 25-hydroxyvitamin D to acceptable levels, but compliance was an issue that needs to be overcome.
In this study, investigators studied whether a weekly dose of 10,000 IU vitamin D could be substituted for this daily 2000-IU dose, and investigated the effects of vitamin D supplementation on immune function in an environment known to suppress immune function. The main objective of this study was to determine if a weekly dose of vitamin D is just as effective as a daily dose to reach a desirable vitamin D status, and to maintain that level for the duration of the mission. Compliance is more difficult with a daily supplement, and a weekly supplement would be more desirable. A secondary objective was to determine if vitamin D supplementation improves immune function of subjects wintering over in Antarctica, a population known to have altered immune function.
The Specific Aims were:
1. To determine the time course and magnitude of changes in vitamin D status during wintering over in Antarctica, with or without vitamin D supplementation.
2. To determine other markers of bone and calcium metabolism (such as serum calcium, 1,25-dihydroxyvitamin D, and parathyroid hormone) before and after vitamin D supplementation to determine the effectiveness of supplementation.
3. To determine the relationships between vitamin D status and immune response. A polymerase chain reaction assay will be used to determine the reactivation patterns of varicella-zoster virus, a causative agent of chickenpox in children and shingles in adults.
Vitamin D supplementation
Subjects were trained to collect diet records and were asked to record all food items consumed for 1-week periods three times during the study period. Although foods are generally not rich in vitamin D, it is possible that wintering polar explorers will consume a relatively large amount of fish and therefore a substantial amount of vitamin D could come from the diet. Height and body weight were measured at the beginning of the study, and body weight was measured once per month during the remainder of the study. The efficacy of vitamin D supplementation was documented as the dose that maintains mean serum 25-hydroxyvitamin D concentration above 80 nmol/L over the course of the winter without changing serum calcium levels.
Saliva samples were collected for 10 consecutive days before each of the three blood draws. Samples were stored frozen until they were processed. Immune function was tested by studying reactivation of varicella-zoster virus (VZV), which causes chicken pox in children and shingles in adults. This virus is said to be widespread in adults, and reactivation of VZV has been found to occur during space flight in most astronauts. The investigators used a polymerase chain reaction (PCR) assay to determine the reactivation patterns of VZV. Viral DNA will be extracted from saliva samples.
Sample Collection and Processing
Blood samples were collected by standard phlebotomy techniques. All samples were collected in the morning after an 8-hour fast. About 12 mL of blood (two 6-mL serum tubes) were collected at each of the three blood collection sessions. Blood was processed, serum was collected, and aliquots were stored at minus 70 degrees Celsius. Samples were transported on dry ice to the Nutritional Biochemistry Laboratory at the Johnson Space Center in Houston, TX, and indices of vitamin D, bone, and calcium metabolism were measured, including serum 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, PTH, BSAP, N-telopeptide, and calcium.
All subjects recorded food intake for 1-week sessions at the beginning, middle, and end of the supplementation period (a total of three 1-week sessions were collected for each subject). Nutrient intake was calculated from the food logs using the Nutrition Data System for Research developed by the Nutrition Coordinating Center, University of Minnesota, Minneapolis, MN. Body weight was measured once per month using a calibrated scale.
Results indicate that a once-daily 2,000-IU and a once-weekly 10,000-IU vitamin D3 supplement are equally effective in increasing vitamin D status in subjects not exposed to sunlight for 6 months. Furthermore, the response to supplementation depends on both BMI and baseline vitamin D concentration. Importantly, the roles of vitamin D status and stress in immune responsiveness to viral reactivation interact. These findings represent valuable information about vitamin D, and provide evidence targeted at gaps in our understanding of vitamin D.
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