Five Things You Should Know About Vitamin D

We asked an expert how and why you need to be getting vitamin D.

Of all the vitamins and minerals, vitamin D is arguably the most controversial.

A recent local study linked vitamin D deficiency to osteoarthritis, and research has shown in the past that not getting enough may be tied to high blood pressure, obesity, and depression—but because the sun is the most common source, it can be hard to weigh vitamin D’s benefits against risk of conditions such as skin cancer.

Rachel Cheatham, an assistant professor at the Tufts University Friedman School of Nutrition Science and Policy and the founder of nutrition group Foodscape, told us five things you might not know about vitamin D.

1. Vitamin D has many uses. “You have to appreciate how many functions vitamin D really has,” Cheatham says. “It goes way beyond bone health. It aids in immunity, reducing cancer risk, our emotions and cognition, plus a lack of it can lead to depression.”

2. There are sources of vitamin D other than the sun… Egg yolks, milk, cod liver oil (which is found in salmon and tuna), some types of fish, mushrooms, and ricotta cheese all contain the substance. If you’re a vegan or vegetarian, look for vitamin D-fortified foods. Cheatham says those who don’t eat meat should “always flip the carton around to check,” since vitamin D content usually depends on the brand, not the general product.

3. …but sun exposure is okay—in moderation. “Sunlight really will top off vitamin D levels; there’s been plenty of research that proves that,” Cheatham says. Nonetheless, she notes that there’s no real rule that measures the benefit of vitamin D against the risk of skin cancer, so it’s still crucial to wear sunscreen and protect yourself from UV light. “There’s no recommendation that says, ‘This many minutes outside will give you enough vitamin D without getting skin cancer,'” she says.

4. The recommended dose is up for debate. Past guidelines have called for 400 international units of vitamin D each day—about how much you’d get from a serving of swordfish. But, Cheatham says, “many [researchers] are now claiming we need as much as 10,000 [IU per day], which would mean a lot of us are incredibly deficient and just don’t realize it.”

5. It’s not technically a vitamin. Despite its name, vitamin D is technically a hormone, Cheatham says. “Why we all call it a vitamin is really a question for the history books,” she says. “It just gets lumped in.”