Vitamin D

As well as depending on sunlight for the majority of our food, at least indirectly, we as human beings also need sunlight for the production of vitamin D. This important vitamin is produced in our skin as a result of exposure to UV light, particularly UVB.

Vitamin D is necessary for our bodies to properly process calcium, and is therefore needed to help build and maintain strength in our bones. Without adequate levels of vitamin D, the body is unable to properly absorb calcium from food and instead re-absorbs it from the bones, weakening them and preventing the formation of new, strong bone.

Vitamin D is also beneficial for the strength of our muscles, and promotes anti-tumour activity by our immune systems.

Sources of Vitamin D

Vitamin D is rarely available in common foods, other than those deliberately fortified with it, such as breakfast cereals and dairy products. Oily fish (particularly herring and salmon), cod liver oil, and mushrooms (especially when sun-dried or irradiated with UV), are good sources, however.

By far the best source of vitamin D is simple exposure of your skin to UVB. Not much exposure is needed: about 10 to15 minutes in the Sun, with your arms, hands and face exposed (and without sunscreen), 2 to 3 times per week is all that is necessary, provided the Sun is strong enough (UV Index of 3 or higher).

Sufficient Sun strength occurs daily (subject to cloud cover) in spring and summer at higher latitudes such as Europe and northern USA, and all year round in the tropics.

If you are particularly pale-skinned, even less exposure may be sufficient, while if you are dark-skinned substantially more will be required. This is why vitamin D deficiency is particularly prevalent among dark-skinned people at higher latitudes.

Vitamin D generation in the skin increases with further exposure to a maximum level. After this, any excess vitamin D produce is naturally destroyed, so it is not possible to overdose on vitamin D through UVB exposure (although there may be other consequences of such exposure). It is possible to overdose on vitamin D from dietary sources, however, but the levels needed for toxic effects in adults are very high. The safe limits for children and especially infants are much lower.

Vitamin D is also stored in the body, to a certain extent, so that the loss of adequate Sun strength in autumn and winter at higher latitudes isn’t a great problem, provided adequate levels were built up over the summer.

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