27th October, 2009

Researchers are suggesting that lower vitamin D availability in the winter months may explain the seasonal nature of flu outbreaks and why swine flu has been particularly virulent in Scotland.

A number of genes are known to be regulated through the interaction of vitamin D in the form of 1,25(OH)₂D and its receptors with DNA. 1,25(OH)₂D has a variety of effects on immune system function, which may enhance innate immunity and inhibit the development of autoimmunity. The vitamin D receptor (VDR) is expressed by most cells of the immune system. Those with low blood levels of vitamin D (25[OH]D levels <17.8 ng/mL) have been found to have a 26% increased risk of mortality from any cause.

The Times reports that Scotland has 530 confirmed cases of swine flu, 441 possible cases and 300 clinically diagnosed possible cases, a total of more than 1,200. Comparable countries with much larger populations are relatively unaffected. England, with ten times the people, has 1,062 cases, Austria 7, Portugal 3, France 80, Germany 170, Spain 488 and Ireland 12. It may be the case that the explanation for this is the prevalence of vitamin D deficiency in Scotland.

Exciting as the new research is blanket supplementation is not recommended; vitamin D is a fat soluble vitamin and as a result can be toxic. Vitamin D toxicity (hypervitaminosis D) induces abnormally high calcium levels (hypercalcemia), which could result in bone loss, kidney stones, and calcification of organs like the heart and kidneys if untreated over a long period of time. It is however vital to ensure good vitamin D intake by combining good amounts of sun exposure (about 45 minutes per week) with a diet that includes oily fish, eggs and some milk. Bear in mind that the application of sunscreen with an SPF factor of 8 reduces production of vitamin D by 95%. Supplementation of up to 10μg (400IU) is safe; intake at this level is recommended for the elderly, who have a reduced capacity to synthesize vitamin D in the skin, and those at risk of deficiency such as Islamic women using the hijab. An abundance of new research suggests 5-10μg may also be needed in the winter months among those living in the northern hemisphere.