Sunlight is both a blessing and a curse. On one hand, your body needs it to jump-start vitamin D production. On the other, too much sun on your skin could lead to cancer. And when it comes to giving advice, there’s no one-size-fits-all approach. There are just too many variables.

The sun’s intensity can vary. The time of day, season of the year, cloud cover and your location all matter. (The sun is stronger as you go closer to the equator and higher in altitude.) Then you have to factor in personal variables, such as skin tone and clothing.

In one study, researchers found that the amount of sunlight required to hit vitamin D requirements in Spain ranged from 7 minutes in July to more than 2 hours in January. But those numbers would likely be higher in Montana and lower in Florida. (Optum Perks, on the other hand, works the same in all 50 states. Download our discount card to start saving.)

To help solve the sunlight puzzle, we spoke with Barry Goldman, MD, a dermatologist in New York City. He’s been advising people on how to take care of their skin for more than 2 decades, so he has a lot to say about sunlight.

How does the body turn sunlight into vitamin D?

Dr. Goldman: There is a precursor of vitamin D in your skin that is activated by sunlight. It moves through the body to become vitamin D.

Why is vitamin D important?

Dr. Goldman: Active vitamin D helps increase the amount of calcium your gut can absorb from food into your bloodstream. [Learn more about the benefits of vitamin D.]

How much vitamin D can you make in a day?

Dr. Goldman: Somewhere around 15 to 20 minutes a day exposing your arms would be a fine estimate for most people. You can’t make up for perceived sunlight deficiency with a trip to Barbados; you could end up with a sunburn that leads to a deadly melanoma or other skin cancer.

It’s hard to say how much exposure you should get, since skin pigmentation affects how much radiation your skin absorbs. Darker skin can go a little longer, but very light skin might only need a few minutes. Instead of risking sunburn, taking a vitamin D supplement (under medical guidance) is a good option for everyone.

Can my body stockpile vitamin D?

Dr. Goldman: Vitamin D, like other fat-soluble vitamins, is stored in your body’s fatty tissue, so your body can mobilize reserves. You don’t need vitamin D every day.

How else does healthy sunlight exposure affect our well-being?

Dr. Goldman: Sunlight has real benefits: It puts you in a good mood and keeps your circadian rhythm [your body’s internal clock, which determines when you’re tired or energized] on schedule. Many people also find it easier to exercise outside, and 3 workouts a week have been proven to lower blood pressure and raise HDL (good) cholesterol. You could argue that sunlight indirectly affects well-being in all these ways. If you’re feeling depressed from lack of sunshine, especially in winter, you might consider light therapy.

What are the risks of too much sunlight?

Dr. Goldman: Sunlight delivers ultraviolet radiation. Unprotected UV exposure, from sun or indoor tanning devices, is a known risk factor for developing skin cancer. How much you absorb varies, depending on your skin tone. People with darker skin may need more exposure to make an adequate amount of vitamin D. Because of their darker skin, they will also be less likely to get skin cancer. However, people of color are often diagnosed at a later stage of skin cancer than people with light skin.

People who are pasty white will make vitamin D faster, but they have a higher risk of skin cancer if they get direct exposure to sunlight. They would need more sunscreen and minimal exposure. They should take supplements if they need more vitamin D. There really is no such thing as a safe tan.

To what extent does sunscreen halt vitamin D production?

Dr. Goldman: Most doctors think that even when you wear sunscreen, you can still get enough sunlight to activate precursors of vitamin D through your skin. But you need to strike a balance, and that will be different for every person. You’re less exposed to sun in winter, but you can still get a sunburn on your face. Skiers know this. Also, UV rays cause premature aging. So there’s an argument to be made for everyone to wear sunscreen year-round. [Here’s how to get more vitamin D in winter.]

How do you know if you’re getting too much sun?

Dr. Goldman: Almost every one of my skin cancer patients has a story about that one bad sunburn they had, when their skin turned red and peeled for days. Peeling skin is a bad sign. It is your body’s way of getting rid of damaged cells. That’s when you know you’re getting too much sun. Even one sunburn increases your skin cancer risk. Cumulative sun also increases your skin cancer risk. As the saying goes: Everything in moderation.

As a dermatologist, how do you balance sunlight exposure in your life?

Dr. Goldman: Heart disease is still the leading killer in America, even after COVID-19. I would argue that regular exercise is extremely important. I like to do that outdoors, which means I need to manage my sun exposure.

If I’m riding a bike or jogging at 7 a.m., I don’t always wear sunscreen because the UV rays aren’t as strong, especially in winter. In most places, the sun is strongest between 11 a.m. and 3 p.m. There’s way too much strictness in saying all sun is bad sun, but there is a tradeoff in terms of aging and skin cancer.

According to the American Academy of Dermatology, there is no scientifically validated safe threshold level of UV exposure from the sun that allows for maximal vitamin D synthesis without increasing your skin cancer risk. But be sure to check the UV Index before you head out to see what sort of exposure you’ll be getting. Above 6 is high; 0 to 2 is low. [The U.S. Environmental Protection Agency considers 8 and above “very high to extreme.” You can find the UV index listed in online weather reports or in your preferred weather app.]

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Additional source
Sunlight and vitamin D: Science of the Total Environment (2016). “Solar ultraviolet doses and vitamin D in a northern mid-latitude.”