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One recent study in the Journal of the American Osteopathic Association (JAOA) concluded that slathering yourself in SPF 15 or higher sunscreen every time you go outside could cut your body’s vitamin D production by 99%.
“Your body takes UVB light and converts it to vitamin D3, which in turn regulates the uptake of calcium in the intestines,” says Michael Olding, MD, a professor of surgery at George Washington University. “But the irony [when it comes to sun exposure] is that the same thing that’s good for you can also be bad for you.”
Of course, Olding is talking about skin cancer. And in his view, the cancer risks associated with unprotected sun exposure far outweigh the risks of too little D. “I think the amount and magnitude of [health] problems you risk from low vitamin D are many times lower than the risks of unprotected sun exposure,” he says.
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In many ways, you can equate sun exposure to other carcinogens, such as cigarettes. Less is safer. But there’s no lower limit that guarantees you won’t raise your cancer risks, Olding says. He also points out that, while vitamin D shortages seem to be on the rise, there’s still expert doubt about whether lower D levels are leading to widespread health issues among American adults.
Other experts repeat this point.
“We see people with low vitamin D, but it’s not clear if this has any clinical relevance,” says Zaineb Makhzoumi, MD, an assistant professor of dermatology at the University of Maryland School of Medicine. So while some research has linked low D with health issues, it’s far from certain that insufficient vitamin D is the cause of those health problems, she says.
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On the other hand, there’s no doubt at all that spending time in the sun without protection could give you skin cancer. “I’m not saying you’ll die from melanoma if you’re exposed to the sun, but as far as skin cancer is concerned, there is no ‘safe’ amount of sun exposure,” Olding says.
So How Much Sun Is Appropriate?
That’s tricky, and many experts disagree on what amount is necessary.
Both Olding and Makhzoumi say any unprotected exposure is risky. Makhzoumi adds, “I think the amount of sun you need to get vitamin D is so little, you’ll probably get it from driving and having sun hit your hands without sunscreen on.”
Unless you’re spending nearly all your time indoors—a reality for some older adults in care facilities—you probably get enough sun even if you’re diligent about using sunscreen when you go outdoors.
“It also really depends on the patient,” says Jeremy Davis, MD, a surgeon and clinical instructor at UCLA Health. “If you have darker skin and no family history of skin cancer, then I think short amounts of time—maybe 10 minutes a day—of unprotected sun won’t raise your risks unduly.”
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But if you have very light skin and a history of skin cancer? No amount of unprotected sun is safe, he says. “I’d say take a vitamin D supplement,” he adds. (More on those in a minute.)
Research seems to support all of these takes. The authors of that JAOA study concluded that as little as 5 minutes of unprotected midday sun, just twice a week, is enough to supply your body with adequate D.
So What Should You Do?
Unless you have reason to believe your D levels are low, you’re safest option is to apply sunscreen every time you’re planning to spend time outdoors in the sun. (Here is a list of safe options, and those that might contain harmful chemicals.)
Chronic joint pain, low energy, and broken bones are all signs you may be low in D. If you don’t have those symptoms but you’re still worried, ask your doctor to check your vitamin D levels. It’s a simple blood test—and a great way to put your mind at ease.
You could also take a vitamin D supplement. While there’s some lingering questions about whether taking D3 in pill form can replace what you’re not getting from the sun, Olding and Davis agree it’s a worthwhile option.
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“I personally have low D, and I take a vitamin D3 supplement,” Olding says. As for a dose, he recommends 1,000 to 2,000 IU per day, assuming you're not severely deficient. If you are, your doctor may need to write you a prescription for a higher dose. Ensuring your diet includes healthy sources of vitamin D—foods like salmon and other fatty fish—is also a good idea, Olding says.
You also want to be sure you’re getting enough calcium in your diet. While a D supplement alone may not be sufficient, Olding says taking D3 with calcium seems to protect older adults from bone problems like fractures. Kale, broccoli, and all dairy products are good calcium sources.
None of these options is perfect. But when it comes to balancing the risks of low D and skin cancer, erring on the side of caution—and keeping your skin protected from the sun—seems like the safest bet.