This research and its findings should reassure people that the benefits of sunscreen outweigh concerns about its possible effects on vitamin D levels in the body, says Antony Young, the study’s lead author and a photobiologist at King’s College London.
Such concerns have been based primarily on laboratory studies, Young and his colleagues point out in their paper. By contrast, their study was a “field trial.” It tested the use of sunscreens on real people in a real-life situation — while they were vacationing in a particularly sunny locale.
“Sunlight is the main source of vitamin D,” said Young in a statement released with the study. “Sunscreens can prevent sunburn and skin cancer, but there has been a lot of uncertainty about the effects of sunscreens on vitamin D.”
The new study demonstrates, he added, that “even when used optimally to prevent sunburn, [sunscreens] allowed excellent vitamin D synthesis.”
For the study, Young and his colleagues recruited 79 healthy adults living in Poland. All the participants had either type II (“usually burns, tans minimally”) or type III (“sometimes mild burn, tans uniformly”) skin, based on the Harvard-developed Fitzpatrick classification system.
Sixty-two of the participants were sent to Tenerife, the main island in Spain’s Canary Islands off West Africa, for a week in the sun. (I suspect finding volunteers for this study was not difficult.) Tenerife has a very high UV index, similar to that of south Florida, the researchers note in their paper.
The vacationing participants were then divided into three groups. Two groups (20 participants in each) were instructed to apply a tube of sunscreen with a sun protection factor (SPF) of 15 to their skin three times a day: in the morning, at mid-day and again at mid-afternoon. One of these groups was given a broad-spectrum sunscreen, which provides balanced protection against both UVA and UVB rays, while the other received a non-broad-spectrum sunscreen, with low UVA protection. The third group (22 participants) was told to use their own sunscreen, and they weren’t instructed on how or when to use it.
A fourth group — the “control” (17 patients) — remained in Poland.
All the participants were asked to keep diaries during the week of their sun exposure. Blood tests to measure their vitamin D levels were taken 24 hours before and 24 to 48 hours after the vacationing groups went to Tenerife. Their level of sunburn was also measured.
The study found that the use of sunscreen has no meaningful effect on vitamin D levels. All three groups that went to Tenerife experienced “highly significant” increases in their vitamin D levels when compared to the group that remained in Poland.
Interestingly, the broad-spectrum sunscreen was associated with higher Vitamin D synthesis than the non-broad-spectrum one — probably because it allows for more UVB rays to penetrate the skin, say the researchers.
The study also found that group of vacationers who used their own sunscreen (without being given instructions on how and when to apply it) experienced significantly more sunburn while in Tenerife than the other two groups who went there.
Limitations and implications
The study comes with several important caveats. It included a relatively small number of participants who live in one city in Poland and who have similar skin types. The findings might not apply to people with either darker or lighter skin types.
Furthermore, the participants were not randomly assigned to the study’s groups. The people who chose to stay behind in Poland may have been different from the other groups in ways that affected their vitamin D levels. Indeed, the people who remained behind tended to be older than those who went to Tenerife, and vitamin D synthesis is known to decrease with age.
Still, the fact that the study was conducted under “real life” holiday conditions rather than in a laboratory gives its findings some weight.
In another study, published in the same issue of the British Journal of Dermatology, an international team of researchers reviewed 75 field trials, observational studies and experimental studies (ones conducted in a laboratory using artificial light) that had looked at the effect of sunscreen on vitamin D production between 1970 and 2017.
That paper also concludes that using sunscreen — even when applied frequently and generously, as advised by health officials — has no significant effect on the body’s production of vitamin D.
In fact, the authors of the paper say their review suggests that “other photoprotection behaviour (such as seeking shade, wearing protective clothing and long sleeves) may have more impact on vitamin D status than sunscreen use.”
Unfortunately, several of the authors of that review are employed by L’Oreal, a company that sells sunscreens along with other cosmetic and beauty products. The review’s findings, therefore, have to be viewed through that conflict-of-interest prism.
FMI: You can read both studies at the British Journal of Dermatology’s website.