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Last year, a man in the United Kingdom died after ingesting too much vitamin D. A coroner’s report found that the man, who was 89, had severe hypercalcemia caused by vitamin D toxicity. In the nine months leading up to his death, according to the assistant coroner, he’d been taking such a high dosage of supplements that the levels of vitamin D in his blood were at the maximum recordable level. His death made international headlines and raised the question: How much vitamin D is too much?
Before you toss out all the vitamin D in your medicine cabinet, there are some important details to consider here. First, vitamin D toxicity is very rare—and it’s most often caused by regularly ingesting doses of 50,000 IU or higher, especially when taken without the guidance of a medical professional. For context, the National Institutes of Health recommends most adults get somewhere between 600-800 IU of vitamin D daily. (Every IU, or “international unit,” is equal to 40 micrograms.) Taking 50,000 IU daily puts at more than 60 times the recommended amount—an incredibly high dose.
There’s a lot that scientists are still researching when it comes to vitamin D, but at the recommended dosage, it’s believed to be both safe and beneficial for most people. Vitamin D helps our bodies absorb and retain calcium, and it’s been loosely connected to mood regulation, which may help boost other treatments for depression.
A new study found that vitamin D can even help prevent or lessen the severity of some kinds of cancer. The study, which was conducted over a period spanning more than two decades and published earlier this month, showed that postmenopausal women taking 400 IU of vitamin D3 daily had a 7% reduction in cancer mortality. (Postmenopausal women taking vitamin D3 did, however, show a 6% increase in cardiovascular disease mortality.)
So how do you know if you’re getting enough vitamin D, or too much? If you’re unsure, the first step is to see a doctor. There are so many factors that can affect how much vitamin D any one person needs—things like the climate where you live, how often you’re able to go outside, your level of physical activity, the clothes you wear, your and even your weight.
If that last variable is surprising, it shouldn’t be, says Craig Primack, MD, FACP, FAAP, FOMA, a physician specializing in obesity medicine. Most vitamins are water-soluble, meaning any excess gets washed out of the body, so to speak. But vitamin D is one of four fat-soluble vitamins, the others being vitamins A, E and K.
“Fat-soluble vitamins get deposited in your fat stores, where they build up. And people with obesity have bigger fat stores,” Dr. Primack, the Senior Vice President of Weight Loss at Hims & Hers, says.
That means there’s just more places for vitamin D to be spread in the body after being consumed, making its overall concentration lower. (While it’s true that obesity tends to be correlated with lower vitamin D levels, there’s no conclusive evidence suggesting an inverse relationship in which higher vitamin D levels directly lead to weight loss.)
“Many people who have obesity have to supplement their vitamin D in order to have a normal amount,” Dr. Primack explains.
But what exactly is a “normal” amount? For most people, Dr. Primack says, that means somewhere between 30-65 nanograms per milliliter (ng/mL) on a blood test, which you can typically get through a combination of nutrient-rich foods and supplements with a doctor’s supervision.
Many people don’t think to mention supplements to their doctors, but doing so is important for many reasons, including some you may not expect: While it’s true that vitamin D is rarely harmful on its own in recommended doses, it can interact negatively with other medications.
“I think when people hear supplement, they think, ‘Oh, I can just take any amount of this, and it's not going to hurt me. It'll only do good,’” says Luke Wright, Pharmacist-In-Charge at Apostrophe. But a handful of drugs do have interactions with vitamin D, he says, including diuretics like hydrochlorothiazide. (Taking both can cause increased risk of hypercalcemia.)
For people who may be wary of supplements, there’s another key way to modulate the body’s vitamin D levels: The time you spend in direct sunlight also directly affects how much of the “sunshine vitamin” your body receives. But making sure you get enough that way isn’t as straightforward as it might seem.
“In the winter months, even with some sunlight, it’s just not strong enough for most people to get the needed 20 minutes a day,” Dr. Primack notes. “Most people put on sunscreen and don’t go out in the sun with a T-shirt and shorts for long periods of time, so they don’t get enough vitamin D.”
Sunlight can also have significant benefits for mental health, affecting not just overall mood but also cognitive function. With summer coming up, this is something you can prioritize adding into your routine (don’t forget the SPF!).
Odds are, you probably don’t need to worry about getting too much vitamin D, but if you’re ever concerned about your levels, talk with a doctor to help figure out what’s right for you.
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