If your childhood was anything like mine, you may have found yourself being fed multi-vitamin tablets or the dreaded spoon of cod liver oil by well-meaning adults. We all know that vitamins are beneficial, but there is growing evidence to suggest that vitamin D may be even more important than we have been led to believe. The vitamin may even provide protection against cancer, heart disease, and even sleep disorders.
In the past, vitamin D deficiency was marked by an increased risk of fractures, rickets, and osteoporosis. This is because vitamin D’s main function is to aid in the uptake of small molecules like calcium, magnesium, and phosphates from the intestines. Calcium uptake is particularly important for maintaining bone density.
A recent study has determined that higher vitamin D concentrations are associated with a lower risk of cancer in Japanese populations. It has been found that vitamin D reduces cell proliferation and differentiation in malignant cells. Other studies have found an association between vitamin D levels and a reduced risk of coronary heart disease. Even more studies link vitamin D deficiency with fatigue. Given how such diseases plague our societies, why do so many of us not get our daily allowance of vitamin D?
It has much to do with how we obtain – or don’t obtain – our vitamins. Vitamin D is made up of couple vitamers (forms): D2 and D3. D2 is formed in yeasts and fungi when hit by ultraviolet light. D3 is an animal-based source and formed from cholesterol when sunlight hits the skin. D3 formation in our skin is a delicate balance between the levels of the pigment melanin – the main determinant of skin colour – and the intensity of sunlight. A higher concentration of melanin is associated with a darker skin colour and protects well against UV ray damage. However, it also means that the conversion of cholesterol to vitamin D is slowed.
Evolutionarily speaking, this makes sense, as we can observe a decrease in skin pigmentation with increasing latitude and decreasing sunlight intensity. As sunlight intensity decreases, less melanin is required to protect against UV rays and to make use of the limited light to synthesise vitamin D. A notable exception to this pattern is the Inuit of Northern Canada. Due to their high latitude, one would expect them to have a pale skin colour, yet their fish heavy diet provides them with all the vitamin D they require. Therefore, their skin has not reduced in pigment concentrations.
Although our skin does a good job of synthesising this necessary molecule, during months where there is limited sunlight, it simply isn’t enough. Current guidelines suggest a daily intake of 10 micrograms of vitamin D, which would likely require some supplementation in the form of vitamin tablets or diet changes. It must be stressed that vitamin D overdose is possible via supplements; however, it seems our parents were onto something with the cod-liver oil after all.
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