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Vitamin D is a vital nutrient in your body, and one of the main sources of vitamin D for humans is exposure to UVB radiation from the sun. However, UV also causes skin cancer and skin aging, so sun protection (sunscreen, protective hats, protective clothing) is important. How should we balance the two? This is a very controversial topic and there aren’t a lot of clear guidelines, so here’s my best attempt at deciphering the prevailing wisdom.

What is Vitamin D?

Vitamin D is an important vitamin that has many possible roles in your body. It’s best known for maintaining your calcium levels and preventing osteoporosis and soft bones, but it’s also suspected to have a role in a whole bunch of other processes including cancer prevention, heart disease, metabolic syndrome and obesity.

Vitamin D is naturally produced in your skin upon exposure to UVB radiation. UVB radiation of wavelengths 270-300 nm will produce vitamin D in your skin, with maximal vitamin D synthesis at 295-297 nm. The amount of vitamin D produced varies with factors like where you live (latitude), time of year, time of day and your skin colour. Daily exercise also helps the body produce vitamin D.

There are a few foods which are sources of vitamin D, including mushrooms, fatty fish, liver, cheese, and specially fortified foods, but this doesn’t contribute to more than 10% of an average adult’s vitamin D requirements. Vitamin D supplements are also available.

It’s estimated that 23% of Australian adults are vitamin D deficient, while 32% of US adults are deficient.

Does sunscreen affect vitamin D?

Since sunscreen reduces the amount of UVB reaching your skin, it seems logical that sunscreen would decrease vitamin D production, but a 2009 study found that it has little effect. The reason seems to be that most people don’t apply sunscreen sufficiently, and even if you think you do, the spots that you miss (scalp, between fingers etc.) get enough UV for adequate vitamin D levels.

There are some sunscreens being developed that absorb harmful UV wavelengths while allowing vitamin D-producing UVB to pass through. The only one on the market that I know of is SolarD, but I expect this concept will become increasingly popular.

How should I get the right amount of sun?

The easiest way to take into account all of the different factors for vitamin D production is to compare the UV required to the minimum amount of UV that would cause sunburn (the minimal erythemal dose, or MED). Research indicates that exposing 25% of the body to half the MED 2-3 times a week is enough for adequate vitamin D production. Additionally, your body can rely on vitamin D stored in your tissues for 1-2 months, so year-round exposure may not be necessary.

For the US, there are no broad guidelines yet for safe sun exposure. Some researchers recommend 15 minutes in the sun with face, arms and legs exposed 2-3 times a week between 11 am – 3 pm between May and October for people with Fitzpatrick II skin (shorter time if more skin is exposed, longer for darker skin).

For Australians, a set of guidelines have been issued by the Australian and New Zealand Bone and Mineral Society, the Australasian College of Dermatologists, Cancer Council Australia, Endocrine Society of Australia and Osteoporosis Australia in January 2016:

• When the UV index is 3 or above in the middle of the day (most of the year), sun protection is recommended when outdoors for more than a few minutes. Most Australian adults will still produce sufficient vitamin D from incidental exposure during typical outdoor activities, despite taking sun protection measures.
• In late autumn and winter when the UV index is below 3, sun protection is not recommended, and people should go outdoors in the middle of the day with some skin uncovered on most days of the week.

For people in the UK, due to the high cloud cover and low UVB, the NHS recommends that almost everyone should consider taking a daily vitamin D supplement in winter.

Things to keep in mind

Sun exposure isn’t just UVB exposure. The sun also produces damaging UVA, which has no known health benefits, as well as IR and visible light. UVB is highest around noon while UVA levels stay relatively consistent throughout the day, so in terms of cost/benefit, this is the best time to get maximum vitamin D production while limiting exposure to the other harmful radiation types.

Only short, non-burning exposures are required for vitamin D production. Longer sun exposure increases your risk of melanoma and other skin cancers, particularly if you end up sunburnt.

UVB doesn’t pass through glass, so sunlight through a closed window won’t help your vitamin D levels but will increase UVA damage.

Tanning beds produce far more UVA (which causes tanning) than UVB, so they are much riskier than regular sunlight.

You should still wear sunscreen, particularly if you’re using anti-aging ingredients in your skincare regimen, as many of these increase your risk of sun damage.

If you can’t follow the guidelines, you should talk to your doctor about monitoring your vitamin D levels and what steps to take to safely increase your vitamin D (most likely through taking supplements – I take these ones from NOW, but I get them off iHerb). This includes if you’ve had skin cancer or are at high risk of skin cancer, if you wear concealing clothing, if you have very dark skin, or if you’re housebound.

Verdict

• Short periods of sun exposure in the middle of the day will provide you with adequate vitamin D while minimising your risk of skin cancer and photoaging.
• Continue avoiding sunburn and UVA.
• Sunscreen is unlikely to make you significantly more vitamin D deficient than you already are.

Further Reading

DG Hoel, M Berwick, FR de Gruijl & MF Holick, The risks and benefits of sun exposure (open access), Dermato-Endocrinology 2016, 8, e1248325.

Position statement – Risks and benefits of sun exposure and vitamin D, Cancer Council Australia 2016 (accessed 17 December 2016).

D Kockott, B Herzog, J Reichrath, K Keane & MF Holick, New approach to develop optimized sunscreens that enable cutaneous vitamin D formation with minimal erythema risk (open access), PLoS One 2016, 11, e0145509.

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