Here comes the sun – why vitamin D is known as the ‘sunshine vitamin’

16 Feb 2023

Vitamin D has many health benefits, and not having enough of it could lead to potentially severe issues. Luckily for us, the vitamin has one special quality that sets it apart from the rest: its power to harness the sun and synthesise in our skin when exposed to UV radiation.

Vitamin D is a nutrient that helps the body absorb and retain calcium and phosphorus, which helps build healthy bones. Some studies have also linked vitamin D deficiencies to chronic diseases like autoimmune disease, some cancers, cardiovascular disease, infectious diseases, schizophrenia and type 2 diabetes.

There is also research that suggests that vitamin D can protect against respiratory infections, tuberculosis and asthma exacerbations. It is also believed to influence brain growth, development and overall health, with some studies finding that it decreases the risk of developing dementia and can positively improve symptoms of depression.

Read in Daily Maverick: “Increase your vitamin D intake to decrease your dementia risk, study finds”

On the other hand, deficiencies in vitamin D can lead to severe health problems.

In children, vitamin D deficiency manifests in rickets, which causes soft bones and skeletal deformities. In adults, it can lead to osteomalacia, where the existing bone is demineralised and weakened, resulting in deformity, pain, hypocalcemic seizures, tetanic spasms and dental abnormalities. In 2019, research published in The Lancet estimated that about one in five people living in Africa have inadequate levels of vitamin D concentration.

To maintain healthy concentrations of vitamin D, adults need up to 15 micrograms or 600 international units (IU) of the nutrient every day, according to the US National Institutes of Health.

However, vitamin D can be more difficult to find, since it is present in relatively few foods.

Though it can be found in fare such as fatty fish, egg yolk and mushrooms, as well as supplements, it also has a special superpower: it can be made from sunlight that shines onto the skin. And with a limited number of foods offering this nutrient, this dermal synthesis is a major natural source of vitamin D.

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The “sunshine vitamin” is made when the skin absorbs the sun’s UVB rays, which then breaks down the steroid 7-dehydrocholesterol, to convert it into vitamin D3, one of the two forms of the vitamin, which can then be used elsewhere in the body.

While it is agreed that vitamin D is a vital nutrient and that a key source of it is through chemical reactions in the skin, there is no hard-and-fast rule for exactly how much sunshine is needed.

Broadly, experts recommend 10 to 20 minutes outside each day to reap the benefits. That is equivalent to ingesting an estimated 200 IU of vitamin D – about a third of the suggested daily intake.

However, there are various factors that also come into play to affect this estimate and how much time one should spend in sunlight.

First, lifestyle: how much time people naturally spend outside is linked to how much vitamin D their skin synthesises. People who have indoor, office-based jobs have been found to have lower levels of vitamin D, and are therefore encouraged to make intentional time in their days to go outside and catch some rays.

Skin tone is also a factor when it comes to how much vitamin D is in the body. A study led by Janicke Visser in the Division of Human Nutrition, Faculty of Medicine and Health Sciences, Stellenbosch University, found that participants who had lighter skin tones had higher concentrations of the vitamin in their bodies than those with darker skin tones. Therefore, lighter-skinned people may need less exposure to UVB rays while people with darker skin tones may need more.

As a person ages, the skin produces less vitamin D from sun exposure. According to Harvard Health Publishing, people over 65 only generate a quarter of the amount of vitamin D from the sun as people in their twenties do.

While the evidence is clear that spending time in sunlight is a good way to get a good dose of vitamin D, one does need to exercise caution when it comes to the daily dose.

For vitamin D synthesis to take place, the skin needs to be exposed to solar ultraviolet radiation (UVR) in the UV-B range (290–315 nm).

However, South Africa in particular has high levels of UV across the country, which can damage skin and cause cancer. Therefore, people should still take care when outside, especially in summer, by wearing sunscreen and covering up. The silver lining, though, is that research suggests that wearing sunscreen does not significantly decrease the levels of vitamin D in the skin, and still protects against overexposure to UV rays. DM/ML

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