How Much Vitamin D Does a Person Actually Need?

Vitamin D is known as the “sunshine vitamin.”  Illustration: Jutta Kuss/fStop/Getty Images

Living in New York, I don’t find myself in the sun all that often. Sure, I probably catch a few rays during my brief walks between the subway and either my apartment, office, or local bodega, but by and large, the only light in my life is of the fluorescent variety. Because I know that vitamin D comes from the sun, though, lately I’ve found myself wondering if I’m actually getting enough of it. So I consulted with two experts to find out if my indoors existence is actually detrimental to my health, or if I’m getting enough vitamin D in other ways.

First off, why is vitamin D so important? Well, the very fact that vitamin D is a vitamin means that it’s necessary to live. But on top of that, it’s a “uniquely important vitamin,” Dr. Chris D’Adamo, an assistant professor at the University of Maryland School of Medicine, told me. That’s because it controls the expression of hundreds of different genes, and is involved in the endocrine system and immune system. Registered dietitian Brigitte Zeitlin noted that it also helps the body absorb calcium and phosphorous, which means it helps maintain healthy bones and teeth. If you don’t get enough of it, you might be at risk of rickets and osteomalacia.

So, what’s the link between vitamin D and the sun? Dr. D’Adamo told me that the main way people get vitamin D is through sun exposure. Basically, what happens is that when ultraviolet rays from sunlight strike a person’s skin, vitamin-D synthesis is triggered, according to the National Institutes of Health. Zeitlin added that it’s like human photosynthesis — and that’s why vitamin D is often referred to as the “sunshine vitamin.”

But can you get it from other sources? Yes! While most people get vitamin D from the sun, it also occurs naturally in certain foods (though not that many), and is added to a bunch of other foods. So, if you want to get vitamin D through your diet, you can find it in salmon, tuna, and sardines, as well as fortified milk and some fortified cereals. It can also be found in eggs, butter, mushrooms, and cod liver oil, according to Zeitlin.

How much vitamin D does a person actually need? The amount of vitamin D a person needs, of course, varies depending on their age. But in general, the average recommended daily dose for adult males and females is 600 IU. Dr. D’Adamo said you can usually get enough of it for the day through 10 to 15 minutes of uncovered sun exposure.

How can you tell if you’re getting enough? Unfortunately, the only real way to know if you’re getting enough vitamin D is through a blood test, which your doctor will generally do during your annual physical (but you can also request a test). Most people with vitamin-D deficiencies don’t have any symptoms, but Zeitlin noted that some may experience fatigue and muscle pain. You’re likely getting enough of it through general sun exposure in your day-to-day life, but certain people are at risk for low levels of vitamin D, particularly those with darker skin or people who live in Northern areas (especially during the fall or winter). “I recommend to pretty much everybody to get a vitamin-D blood test,” Dr. D’Adamo said.

What do I do if my vitamin D levels are low? Well, if they’re very low, your doctor will probably prescribe you some sort of vitamin-D supplement. But if not, it might be a good idea to take an over-the-counter vitamin-D supplement. Dr. D’Adamo added that most multivitamins contain vitamin D — but not all. So if you’re hoping to get enough through your daily gummy multivitamin, just check the label to be sure it has vitamin D beforehand.

How Much Vitamin D Does a Person Actually Need?