Vitamin D Deficiency and Stress
UVB exposure is limited by geography, as the lower arc of winter sun causes UVB rays to be deflected off the earth’s atmosphere. This is reflected in the widespread vitamin D deficiency of those populations living at latitudes over 37 degrees, including southern Australia and New Zealand, and is a factor linked to the increased prevalence of autoimmune disease in those regions.Sun avoidance and regional variations highlight the importance of safely managing vitamin D levels with vitamin supplements; at once avoiding the risks of high sun exposure, whilst compensating for low UVB exposure.
It appears we are hard-wired with a stress response to winter – an evolutionary survival mechanism that guards against severe cold and food shortages. Deepening vitamin D deficiency during winter may act as an environmental cue, triggering an insulin resistant ‘winter metabolism’, as a stress response, to conserve fat mass and energy. However, unlike our ancestors, today we keep warmer and well fed during winter, whilst vitamin D insufficiency and insulin resistance commonly ensue. A recent intervention trial has shown that oral supplementation of vitamin D improves insulin sensitivity over six months in patients with insulin resistance and low vitamin D levels. In the trial, supplementation of 4000IU vitamin D daily over 3 months restored serum 25(OH)D from low levels of less than 50 nmol/L to an optimal level of almost 100 nmol/L, and significantly restored insulin sensitivity, as measured on the HOMA score, over 6 months.
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