Science1 publisher2 min readPublished
Australia now pegs its sun advice to skin tone, season and location
The DNA damage behind skin cancer has a settled mechanism and a dose-response. The benefits attributed to sunlight rest on observational studies that vitamin D supplement trials have not confirmed, and guidance is beginning to split.
The Scientist · Science desk
What happened
- UV light leaves errors in skin DNA that are usually repaired, and the cancer risk comes from accumulation: collect enough of them and the odds rise that one is missed and becomes a mutation.
- The American Academy of Dermatology and the CDC say the best protection is staying out of the sun at peak hours, with a hat, protective clothing and sunscreen for anyone in direct sun from 10 a.m. to 2 p.m.
- Basal and squamous cell carcinomas are rarely deadly; melanoma is much rarer than either but kills around 8,500 people in the United States each year.
- Multiple trials of vitamin D supplementation have failed to show much difference, even as observational work links higher vitamin D to lower colorectal cancer risk and better cancer survival.
- Cancer Council Australia and the Australasian College of Dermatologists issued guidance in 2023 that factors in skin color, time of year and which part of the country a person lives in.
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Why it matters
- constraint Without a supplement that performs in trials, exposure itself is the only variable guidance can set, so the practical argument is about dose and timing.
- contradiction Richard Weller of the University of Edinburgh, lead author of the blood pressure study, says the cover-up advice has gone too far for lighter-skinned people at northern latitudes. Clinicians there are choosing between two named authorities.
- decision One rule for everyone assumes a single UV-to-melanoma relationship, and the JAMA Dermatology finding means that assumption fits some patients better than others.
- precedent Stratified national advice is now a published option. Any body holding a uniform rule has to explain why it declines to stratify.
The two halves of this question do not rest on the same kind of evidence. The damage side has a molecular account. "UV radiation gets absorbed into your DNA and causes little kinks, essentially the DNA equivalent of a typo," Charlene Lam, an associate professor of dermatology at the Penn State Cancer Institute, told Discover [1]. Damage that accrues with dose is why the advice picks out hours of the day at all, and the peak window the American Academy of Dermatology and the CDC name is four hours wide [1]. Discover does not give the number of melanoma diagnoses a year, so the death count it cites cannot be turned into a case fatality rate [16].
The other side is observational, and in each of these studies the people getting more sun chose to get more sun. Covering up and applying sunscreen also cut into the vitamin D the body makes from sunlight [15]. A 2020 study in the Journal of the American Heart Association linked sunshine exposure to lower blood pressure [6]. The National Cancer Institute reports studies finding higher vitamin D levels associated with lower colorectal cancer risk and, in several cancers, with a lower chance of dying of the disease [7]. A study in the Journal of the National Cancer Institute associated sun exposure with better survival among melanoma patients [8].
The supplement trials are the closest thing here to an experiment. Handing people vitamin D in a capsule tests one specific claim: that the molecule is what matters. Multiple trials failed to show that supplementation makes much difference [9]. Two readings survive that. One is that vitamin D helps only when the skin makes it. The other is what Anika Lucas and Myles Wolf of the Duke University School of Medicine put in a 2019 JAMA editorial, that the benefit of sunlight may come from some other factor, or combination of factors, that observational studies are not capturing [10]. The trials varied pills, not sunlight, so they cannot rule sunlight out.
The null results close off the tidy version of the advice, in which you avoid the sun entirely and buy the missing input at a pharmacy.
Answering the dose question takes a trial that varies UV exposure itself and follows blood pressure or survival. Discover says researchers are continuing to investigate the role of sunlight in health, and frames their open question as "How much is too little?" [14]
What to watch
- Whether the AAD or the CDC move from a uniform avoidance rule to guidance stratified the way Australia's 2023 version is.
- Any trial that randomizes UV exposure itself and follows blood pressure or cancer survival, instead of testing capsule dose.
- Replication of the 2021 JAMA Dermatology finding that UV plays a smaller role in melanoma among people with darker skin tones.