Summertime is here, and with it comes the opportunity to make some vitamin D just by catching some rays. Yet this can leave us in something of a quandary, having to navigate the fine line between adequate sun exposure and the risk of sunburn.

The UK recommended daily vitamin D intake for anyone over the age of one is 10 micrograms (ug) or 400 international units (IU). Achieving this through sunshine, however, can be a challenge; especially in children whose skin has been slathered with high factor sunscreen.

Lotions with an SPF of 30 or more have been found to reduce vitamin D synthesis by 95%.

What is vitamin D?

An essential nutrient Vitamin D has numerous roles and more recently has been speculated to reduce the severity of Covid-19. It is, however, more commonly known for its importance in bone health; notably it aids absorption of calcium, which is necessary for skeletal growth and bone health.

A concern with children is that severe vitamin D deficiency can lead to rickets, resulting in poor growth and soft, weak or misshapen bones. Cases are rare but the last decade has seen a rise in rickets-related hospital admissions.

How do we make vitamin D?

When skin is exposed to sunlight, ultraviolet B (UVB) rays convert a chemical in the skin (7-dehydrocholesterol) to vitamin D. From there, it is transformed in the liver and then kidneys into the hormonally active form known as calcitriol. Although getting a bit of sunlight sounds straight forward, numerous factors influence vitamin D synthesis including clothing, time of year, time of day, latitude, air pollution, sunscreen and skin colour.

Also, when it comes to skin colour, a report by the Scientific Advisory Committee on Nutrition highlighted the following advice: of six skin types, those with very light skin or fair/red hair or freckles (types I and II) do not need much time in the sun to synthesise vitamin D, but do have a higher risk of sunburn or skin cancer.

People with darker skin (types V and VI) may need to expose their skin for longer; possibly for three to five times as long as someone with fair skin, according to one small study.

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