Vitamin D homeostasis, bone mineral metabolism, and seasonal affective disorder during 1 year of Antarctic residence

Abstract

Low serum vitamin D and increased parathormone levels were found to be associated with depression and stress in a wintering expedition of 20 healthy male subjects over a period of 1 year in Antarctica. The continuous daylight during summer and the dark polar winter affect endogenous vitamin D production. Long-term effects on bone health need to be studied further.

Purpose: Vitamin D plays a significant role in calcium and bone mineral metabolism and also affects cardiovascular, psychological, and cognitive functions. The ultraviolet B radiation component of sunlight, which shows marked seasonal variation in Antarctica, influences the synthesis of vitamin D. Depression and mood disorders are associated with this extreme photoperiod. In this study, we attempted to gauge the alteration of vitamin D homeostasis in Antarctica and its effect on bone mineral metabolism and mood over a period of 1 year.

Materials and methods: Twenty male subjects who wintered over at India's Antarctic base Maitri (70°45'57″ S, 11°44'09″ E) from November 2010 to December 2011 were studied. Fasting serum samples were collected at baseline, 6 months, and 12 months for serum 25-hydroxyvitamin D, intact parathyroid hormone (PTH), total alkaline phosphatase (ALP), calcium, and phosphate. Beck Depression Inventory (BDI), Positive and Negative Affect Scale (PANAS X), and Perceived Stress Scale were used to measure depression, affect, and stress.

Results: Mild vitamin D deficiency was present in two (10 %) subjects on arrival, which increased to seven (35 %) subjects during the polar winter at 6 months. The mean score on the BDI-II screen for depression was significantly higher during midwinter (4.8 ± 3.9) when compared with the baseline value (2.9 ± 2.1). Only 2/20 (10 %) of subjects met the criteria for minor depression. Higher PTH levels at 6 months correlated with a higher PANAS X score (p = 0.021). The mean values of calcium, inorganic phosphorus, and ALP were comparable during the course of the expedition.

Conclusion: Low light exposure during the dark polar winter, lower vitamin D, and increased intact PTH levels were found to be associated with depression during 1 year of Antarctic residence. The low dietary intake and decreased solar radiation exposure during the polar winter reduce serum vitamin D levels in otherwise healthy individuals, which suggests that supplementation may be necessary.