The other week, after having proclaimed the benefits of Vitamin D and the necessity of getting adequate sun exposure without sunscreen protection, someone shared this ABC news article that loudly pronounces the need to wear sunscreen 24/7. And as a science communicator eager to provide accurate information and afraid that I might have published a misinformed post, I’ve done quite a bit of research to try and understand this issue.
The article in question quoted Terry Slevin, a professor and CEO of of the Public Health Association of Australia who has written extensively on skin cancer, edited a book on the topic and taken on major public roles in cancer prevention projects and organisations. In arguing his case for applying sunscreen as part of a regular daily routine, he made the following claim concerning the possible health effects:
“Importantly, clinical trials have found that people who use sunscreen daily have the same levels of vitamin D as those who don’t.”
The specific clinical trials were not cited and this statement appeared to conflict with some of what I’d previously read in researching about Vitamin D production.
What I’ve learnt
If you’ve ever looked closely at a sunscreen bottle, it says to apply about 45 ml (the size of a shot glass) to your body and re-apply every 2 hours or so. That’s far more sunscreen than most people apply and far more often than many people would consider unless they’re on the beach and it’s extremely hot.
So that means if you put on a smaller amount of sunscreen than is recommended, you probably won’t have a problem getting enough UVB radiation to synthesise Vitamin D … but that means you could also be receiving enough to get sunburnt and increase risk of skin cancers.
So the participants in studies like this one and this one, may have not applied enough sunscreen to see dangerous effects on Vitamin D levels. Tellingly, this 2012 study showed that there was an exponential relationship between sunscreen layer thickness and Vitamin D levels and warned that “re-evaluation of sun-protection strategies could be warranted”. In other words, wearing the recommended amount of sunscreen really limits the amount of Vitamin D your body can produce.
Other research, summarised in this Outside article, claims that while so-called “sun-worshippers” have a higher likelihood of getting skin cancer, they are 8 times less likely to die from it. However, I would be cautious in following their sun exposure advice religiously, given that the magazine is biased towards spending time outdoors.
So it seems from this, that wearing the recommended amount of sunscreen, and applying it as part of a daily routine, as suggested above, is probably going to limit your body’s Vitamin D production. But don’t go straight to the other end of the spectrum and boycott sunscreen all together. Instead, as recommended in the original post, aim for between the 10-30 minute mark of sun exposure. And keep in mind that this depends on location. If the UV index is below 3 (as it is in large parts of the northern hemisphere during winter), you’d have to spend far longer in the sun to get enough UVB, meanwhile in an Australian summer, generally only 2-14 minutes is enough, given that you may get a sunburn in as little as 8 minutes.