There is conflicting information about sunscreen use vs vitamin D. So what should pharmacists advise patients, asks Rod Tucker

With the summer approaching and the prospect of sunny weather, pharmacists’ attention is invariably drawn towards ensuring that they offer sun safety advice to patients.

One important aspect of sun safety is the use of sunscreens, and particularly the agents in them that protect against UVB radiation because this is the component of sunlight responsible for sunburn. Current advice is to use a broad spectrum sunscreen, ie one that protects against both UVB and UVA radiation, because while UVA doesn’t cause burning, it is thought to play an important role in the development of skin cancer.

Whether or not sunscreen use prevents skin cancer was addressed in a Cochrane review in 2016, which concluded that there is still a lack of evidence to support this premise. While it is generally accepted that over-exposure to sunlight, especially UV radiation, leads to the development skin cancer, one major benefit of UV radiation is the production in the skin of vitamin D, which now appears to have several important physiological roles.

Vitamin D deficiency is a worldwide problem affecting over a billion people, though few foods (except for fatty fish such as salmon) contain sufficient amounts of the vitamin. Sunlight is the most important source of vitamin D. The wavelength of UV radiation that produces vitamin D overlaps with the region that causes sunburn and it is therefore conceivable that applying a sunscreen, while offering protection against sunburn, may attenuate production of vitamin D.

This creates a dilemma for health professionals. On the one hand patients require protection from UVB radiation to avoid sunburn but equally, they need some exposure to sunlight to create vitamin D.

But is this a cause for concern in practice? There is evidence that normal vitamin D levels can be maintained despite the use of sunscreens and that frequent use of sunscreens doesn’t appear to be linked with vitamin D deficiency. In contrast, as sunlight exposure can trigger immune-mediated diseases such as cutaneous lupus erythematosus (CLE), patients with the condition require all year round protection and one study identified that such individuals were vitamin D deficient. Another study using a sunscreen with an SPF50+ significantly reduced the production of vitamin D in the skin.

In an attempt to provide clarity on this issue, a systematic review in the British Journal of Dermatology (BJD) looked at all published studies between 1970 and 2017. The authors identified four experimental studies, three field studies and 69 observational studies and concluded that there was little evidence that sunscreen use affected vitamin D synthesis in the skin.

However, an important limitation from the paper was that many of the studies had included products with a low SPF and since SPFs of 15 to 30 are now generally recommended, it was unclear to what extent these higher protection products affected vitamin D levels.

Another somewhat ironic finding from the BDJ article was that sunscreens didn’t appear to diminish vitamin D synthesis simply because in reality few people applied the recommended amount of the product. In a recent study using two SPF 30 products, it was found that when applied at the correct level (2 mg/cm2), no vitamin D was formed in the skin. When the amount applied was reduced to 0.8 – 1 mg/cm2, which is the average level used in practice, sufficient UV radiation entered the skin to form vitamin D.

So, what advice should pharmacists be given to patients to achieve enough vitamin D but avoid sunburn? Enough vitamin D can be produced in the skin by short periods of exposure to sunlight without sunscreens. One UK study has demonstrated that Caucasian adults require nine minutes per day at lunchtime between March and September to create sufficient levels to last throughout the winter and this requires exposure of the forearms and lower legs between June and August. The same group also found that individuals with skin type V (brown skin) require roughly 25 minutes daily over the same period of time.

While pharmacists would normally be expected to offer advice on the correct use of sunscreens, it seems that for once, not providing any guidance is likely to be in patients’ best interest.