How Much Vitamin D Do You Need?

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Any doctor will tell you that your body needs vitamin D to function properly. But if you ask three different docs exactly how much D you need, you'll likely get as many answers. One might say 600 IU per day, which is what the Institute of Medicine suggests, while another may recommend 1,000 IU. And then the third doctor might aim much higher, advocating for 5,000 or even 10,000 IU each day.

This practice has sparked fiery debate among medical professionals in recent years, as vitamin D has been thrust into the spotlight. A fat stack of research now shows that vitamin D keeps our brains healthy, our bones strong, and possibly even helps stave off cancer. And, on the flip side, several studies have linked vitamin D deficiency to various diseases. Nobody really argues these facts. But what doctors are sparring over — and what's causing the huge range in recommended daily vitamin D intakes — is how many people are actually deficient in the first place. The latest news gives the strongest evidence yet that those pushing for more vitamin D were right all along.

Over the past year, two separate groups of researchers, each dissatisfied with the Institute of Medicine's low recommended daily allowance for 600 IU a day, decided to dig back into the studies the IOM had used to come up with its recommendation. Both teams discovered that the IOM had made a giant statistical error. We'll spare you the gritty mathematical details (check them out here if you're interested), but basically, it appears that the IOM miscalculated the amount of vitamin D it takes for 97.5 percent of the population to not be deficient. The researchers insist that when the math is done correctly, the evidence shows that the RDA should be 7,000 IU per day, not 600 IU. In other words, you probably need to be taking a daily supplement of D.


The reason we're severely lacking vitamin D nowadays, much more so than even our parents were, is because we're missing out on the number-one source of vitamin D: the sun. "Vitamin D is a pro-hormone made in the skin upon exposure to sunlight, and production of it is rapid and robust," Cannell says. "Within 10 to 20 minutes without wearing sunscreen, people make between 10,000 and 20,000 IU. But because of widespread sunscreen use, total sun avoidance, and our increasingly indoor lifestyles, our vitamin D levels have fallen drastically."

Let's be clear: Skin cancer is still a very valid concern, as is sunburn, which can permanently damage your skin and cause wrinkles. So nobody is saying it's okay to slather on tanning oil and bake on the beach for hours. However, many experts now think that the long-held advice to never, ever set foot outdoors without wearing sunscreen needs to go.

"SPF 30 sunscreen decreases your body's ability to make vitamin D by 98 percent," says Dr. Michael Holick, an endocrinologist and vitamin D researcher at Boston University School of Medicine. "You always want to protect your face with sunscreen to decrease your chances of non-melanoma skin cancers and wrinkling. However, the rest of your body can handle some sun exposure."

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But running around shirtless in order to get your body making vitamin D obviously won't fly in the wintertime, early spring, or late fall. And even during the summer, on the weekdays, it can be tough to get out midday when the sun is high enough to get vitamin D. That's why so many doctors recommend taking a supplement every day. 

Both Cannell and Holick suggest most people take a vitamin D supplement. Holick says to take at least 2,000 IU per day year-round; he personally takes 4,000. Cannell thinks everyone should take 5,000 IU. And although you technically don't need to supplement on the days that you know you'll be outside when the sun is high, "it's just easier to take it every day than to try to remember when and not to," Holick says.