Is Taking Too Much Vitamin D A Real Concern? (Hint: Probably Not!)

Vitamin D is a vital nutrient involved in immune support, bone health, muscle function, and more.* And yet! Research shows almost half the population1 in the U.S. is insufficient in the beloved vitamin. To reach optimal levels of 50 ng/mL (the true goal for vitamin D sufficiency), food alone just doesn't cut it; you would need an unreasonable amount of vitamin-D-rich foods (like six servings of trout) to even make a dent. 

That, folks, is where supplements come into play: Trusted nutrition and medical experts recommend 5,000 I.U. of vitamin D3 (the body's preferred form) per day to help you get to—and stay!—above that 50 ng/mL threshold. 

If you're familiar with the vitamin D market, you may notice that this recommendation is higher than the average stand-alone supplement typically offers (many include less efficacious doses, like 400 I.U., 600 I.U., 1,000 I.U., or 2,000 I.U.), mainly because brands haven't been keeping up with current science, don't want the hassle of updating their old formulas, or are overly conservative, using the possibility of vitamin D toxicity (or getting too much vitamin D) to back their sub-efficacious doses, according to mbg's director of scientific affairs Ashley Jordan Ferira, Ph.D., RDN.   

Vitamin D's role in calcium absorption and homeostasis in the body is one essential (and helpful) function of the fat-soluble nutrient.* "Vitamin D increases calcium absorption in the gastrointestinal tract," says Sina Gallo, Ph.D., RDN, a nutritional sciences professor at the University of Georgia.

At very high vitamin D doses (we explain what that entails below), "this helpful vitamin D/calcium relationship can tip from normal to not-so-normal, and too much calcium can contribute to kidney stones and blood vessel issues," Ferira explains.

In rare cases, this calcium buildup can cause soft tissues throughout your body (including ones in the cardiovascular system) to harden, which can cause severe concerns. That's why "vitamin D research studies measure calcium levels in the blood and urine," Ferira says, "to ensure the healthy balance doesn't tip to unhealthy, which is very rare in healthy individuals receiving normal doses of vitamin D."

So why the conservative messaging? "Public health guidance, such as that coming from the Institute of Medicine (IOM), needs to be conservative to balance the risk of toxicity in a population," adds Gallo. "A number of other factors affect vitamin D status, including endogenous production (i.e., through sun exposure), adiposity, age, latitude, age, etc., which makes one recommendation for all individuals difficult." A fair reason, but lo and behold, you are an individual and the research is evolving—and we are seeing a slight shift in perspective.

Because of this widespread guidance, though, some supplement brands still tend to err on the lower side of the spectrum and assume the consumer will take more based on their needs. The issue, though, is that this makes people assume that 1,000 I.U. is cutting it (here's why it's not) and that they're going overboard at clinically useful doses (like 5,000 I.U.), Ferira says. 

Here's what we know today: Unless you're taking mega, mega amounts of vitamin D, toxicity isn't really a concern (which means it's time for brands and consumers to catch up). 

As one 2018 review recounts2: "In statements released over the last decade, the Institute of Medicine (IOM) and the Endocrine Society have both concluded that acute vitamin D toxicity (VDT) is extremely rare in the literature, that serum 25(OH)D concentrations must exceed 150 ng/mL, and that other factors, such as calcium intake, may affect the risk of developing hypercalcemia and VDT."

One key point here: that 150 ng/ml mention. That's three times higher than the healthy range clinicians typically recommend (50 ng/ml) for vitamin D sufficiency.

Meanwhile, another 2014 study3 found that taking a whopping 20,000 I.U. of vitamin D3 daily successfully increased whole-body vitamin D levels without participants even coming close to levels associated with toxicity. So, successful, not scary.

Let's also debunk the notion that fat-soluble vitamins are "dangerous," simply because they can be stored in the body. According to Ferira, this is simply untrue. "Just because vitamin D is fat-soluble by design doesn't mean it's toxic at clinically useful doses, like 5,000 I.U.," she says. "In reality, true reports of frank vitamin D toxicity with clinical evidence2 have occurred at 200,000 to 300,000 I.U. per day—yes, you read that correctly—in vulnerable populations like infants or folks with medical issues."

Sweeping statements about fat-soluble nutrients and toxicity simply aren't useful. Ferira continues, "That kind of fear-mongering totally lacks nuance and is an antiquated concept. Let's use another fat-soluble supplement as an example: vitamin A. Yes, you can get hypervitaminosis A (aka, too much vitamin A in the body) and turn orange if you eat a massive amount of carrot smoothies every day for many weeks. The same is true of any massive input that's not the norm and is well above the levels required to achieve sufficiency." 

"Interestingly 10,000 I.U. of vitamin D per day6 is considered a science-backed Tolerable Upper Intake Level (U.L.) from top vitamin D researchers who have actually studied vitamin D toxicity for decades," says Ferira.

To be clear, the U.L. is not the toxic level. Instead, the U.L. is the highest amount of a nutrient the general population can take that likely doesn't have a risk of adverse health effects. "That's an important call-out: general population," Ferira continues. "We're individuals, and the collective science plus your health care provider may determine you personally need less or more than the 'average' person." In fact, some people may even need more than 10,000 I.U. of vitamin D3 per day to reach the desired 50 ng/mL range.* 

Vitamin D toxicity is a real possibility and concern—we're not here to dismiss that—but it seems we need extreme amounts to reach that point. As Ferira puts it: "I think vitamin D is like water, metaphorically speaking. It's absolutely essential and its impact on the body is incredibly widespread. Also, like water, too much of a good thing is harmful to anyone, but it would take some real concerted effort or inadvertent error to get to those kinds of detrimental levels."