Does sunscreen prevent the synthesis of Vitamin D?

Vitamin D is crucial for skeletal integrity and has been linked to numerous other health benefits. Indeed, it enhances the intestinal absorption capacity of calcium and phosphorus, which promotes the mineralisation of bones, teeth, and joints, as well as muscle tone. Over 90% of vitamin D comes from sun exposure, which can then lead to seasonal variations in temperate climates. Therefore, it is essential to get enough sun exposure to ensure optimal levels of vitamin D.

In brief, UVB radiation converts 7-dehydrocholesterol (also known as pro-vitamin D) in the epidermis into pre-vitamin D3. The action spectrum of this reaction indicates that it occurs in the UVB waveband (290 - 315 nm) with maximum efficiency at 295 nm. Formed from pre-vitamin D3 through progressive thermal isomerisation, vitamin D3 then travels to the liver where it is hydrolysed into 25-hydroxyvitamin D [25(OH)D], the circulating form. Subsequently, it is transported to the kidneys for a second hydroxylation to become 1,25(OH)2D (calcitriol), which is the active form of vitamin D.

In order to meet the daily requirements for Vitamin D (estimated at 1,000 IU per day), several studies and reports suggest that spending approximately 15 to 30 minutes per day is sufficient to synthesise Vitamin D.

In recent years, there has been a growing concern that the widespread use of sunscreen, particularly those with a high sun protection factor, could increase the risk of vitamin D deficiency.

What do we know at this stage?

The UV rays from the sun are responsible for sunburn and are also recognised as carcinogenic. Indeed, they are the main risk factor for skin cancers, particularly in populations with fair skin for whom sunburn is a risk factor. Numerous public health efforts have been made to raise awareness about the inherent dangers of sunbathing.

The use of sunscreens is one approach, and randomised trials have shown that they inhibit the development of skin cancers. The role of sunscreens in preventing melanoma has also been supported by large population-based studies.

However, the use of sunscreens appears to have an impact on vitamin D status. The action spectra of erythema and cutaneous formation of vitamin D overlap significantly in the UVB region. Thus, sunscreens that inhibit erythema should theoretically also inhibit the production of vitamin D.

What do the studies say?

Studies on the inhibitory effects of sunscreens on the synthesis of vitamin D have yielded contradictory results. Some authors have found a significant inhibition of its production, while others report no influence of sunscreens on vitamin D.

Sun cream protects the skin from the harmful rays of the sun by filtering UV rays. These consist of different types of UV rays, including UVA and UVB. UVB rays are both responsible for the synthesis of vitamin D, but also for sunburn. As UVB rays are filtered by sun cream, it is reasonable to think that the body may not synthesise enough vitamin D.

A recent study presents conflicting data on the matter. The four experimental studies included in the review showed that the use of sunscreen mitigated any increase in the concentration of circulating vitamin D3 or 25(OH)D, which occurs following exposure to artificially generated UV radiation. Of the 69 observational studies included in the review, 25% concluded that sunscreen use was associated with higher concentrations of 25(OH)D, while 10% concluded that sunscreen use was associated with lower concentrations of 25(OH)D. The authors note that the conclusions of these observational studies are limited by their heterogeneity, study design, and sub-optimal reporting.

This review also included two randomised controlled trials conducted in Australia. In one of these studies, participants were given either a sunscreen or a placebo, and were instructed to apply it daily. In the second study, one group was asked to apply sunscreen daily to their face, neck, arms, and hands, while the other group was advised to apply sunscreen as they saw fit. Both studies compared the concentration of 25(OH)D between the two groups and found no statistical difference. The authors conclude that while there is a theoretical risk that sunscreen could reduce vitamin D levels, current data does not demonstrate a correlation in real-world scenarios.

This conclusion is supported by a more recent study, which demonstrated that during a one-week holiday in Tenerife (Spain), individuals applying an SPF15 sunscreen at the recommended thickness of 2mg/cm2 showed no signs of sunburn and also exhibited a significant increase in serum levels of 25(OH)D. Thus, despite the optimal use of a low sun protection factor sunscreen, these individuals had sufficient vitamin D production.