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Vitamin D is one of the few essential nutrients needed by the body that isn’t naturally present in many foods. Our main source of vitamin D is sunlight – bare skin produces vitamin D in response to the sun’s ultraviolet B (UVB) rays. Our stone age ancestors, with days spent outdoors, sparsely clothed would have benefitted from hours of vitamin D production – today however the story is very different. Most people work indoors, kids play inside and the UK climate means that most are well covered up when outside. 

In fact, getting enough vitamin D from the sun is much more complicated than just stepping outside for a few minutes each day. 

Here’s some of the main points you need to know about vitamin D & sunlight exposure:

Vitamin D & sunlight exposure – it’s complicated!

It’s not possible to give specific recommendations for how long you need to spend in the sun to produce optimal amounts of vitamin D, and that’s because there are many factors that can affect this process.

The paler your skin, the easier it is for your body to produce vitamin D.  For example if you have very pale skin (the type that always burns and never tans) you may get all the vitamin D you need in just 15 minutes exposure. However, if you have dark skin, the type that never burns, it may take 2 hours. Darker skin contains more melanin (a substance that protects the skin against UVB exposure) so it takes longer for this type of skin to produce vitamin D.

Where you live in the world has a massive impact on how much vitamin D you can produce. The further away from the equator you get, the more of an angle the sun hits the earth at  And more angle means less vitamin D-producing UVB rays, especially in the winter, when it can be very difficult for the skin to produce any vitamin D at all. In the summer, the Earth rotates and this angle improves, meaning that these rays are able to reach places further away from the equator as well.

The time of year has a big impact on vitamin D production. In the UK, the angle of the sun in the winter months makes it very difficult for the skin to produce any vitamin D at all. Ideally people in the UK should be topping up their vitamin D with a maintenance dose supplement from October to April.

The time of day has an impact on vitamin D production too. The closer to midday that your bare skin is exposed to the sun’s rays, the better your chances of vitamin D production. Again, this is down to the angle of the sun and a higher chance that the vitamin-D producing UVB rays can get through. Your shadow gives a good clue as to whether you are producing vitamin D. If it’s longer than you are tall (as happens in winter for most of the day) it’s unlikely you are making any vitamin D.  However, in summer, when your shadow is shorter, especially around midday, you are more likely to produce vitamin D.

The more skin you expose, the greater the potential for your body to produce vitamin D – for example, you’ll make more vitamin D if your whole back is exposed than just your face or arms. 

Large amounts of vitamin D are produced when you expose your whole body to summer sun around midday when the sun is high in the sky. Contrary to popular thought, you don’t need to tan or burn to get plenty of vitamin D. For someone with fairly pale skin, just 15 minutes exposure (around half the time is takes for your body to turn pink) can produce 10,000 – 25,000 IU vitamin D.

Skin damage – Spending lots of time in the midday sun without sunscreen may well be the best way to maximise vitamin D production but it’s putting you at higher risk of damage to your skin including cancer risk. The debate over the risks versus benefits of sun exposure continues, with most experts agreeing that a combination of safe sun exposure and supplementation is probably the safest way to keep your levels optimal. 

Summary of factors that affect vitamin D production

✓ Type of skinPale or dark? Paler skin produces vitamin D more easily

✓ Where you liveCloser to equator is best

✓ Time of dayMidday is best

✓ How much skin you exposeLarge areas exposed to the sun’s rays will produce more vitamin D

✓ How old you areIt’s more difficult for your skin to produce vitamin D as you get older

 ✓ SunscreenThis blocks the sun’s vitamin D-producing UVB rays

✓ AltitudeYou make more vitamin D the higher the altitude you’re at (eg. better on top of a mountain than on a beach)

✓ Clear or cloudy skySkin makes less vitamin D on a cloudy day

✓ Air pollutionUVB rays are reflected back into space when air pollution is high

✓ Behind glassYou can’t make any vitamin D when you’re in the sun but behind glass

Consider the risks of skin damage – Experts agree that a combination of safe sun exposure and supplementation is probably the best way to keep vitamin D levels optimal

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