When your body produces vitamin D in response to sun exposure, it basically naturally shuts down production (and increases its metabolism) after getting its fill, according to Gallo. That’s why lifeguards, for example, don’t experience vitamin D toxicity, she says.
However, this isn’t how it works when you get your vitamin D from food or supplements—in which case, it is technically possible (albeit much more challenging than you might think) to get too much, she says. Typically, the first sign that you’re in vitamin D overdrive is hypercalciuria, or too much calcium in your urine. This is usually accompanied by hypercalcemia, or too much calcium in your blood, Gallo explains. Over time, this can contribute to kidney and blood vessel issues.
Unless you’re taking mega (like mega) amounts of vitamin D, though, vitamin D toxicity isn’t really a concern, and the totality of science to back this fact is compelling. Case in point: One study in Canadians found that while taking 20,000 IU of vitamin D3 daily did successfully increase whole-body vitamin D levels, participants didn’t even come close to levels associated with toxicity.
As mbg’s director of scientific affairs Ashley Jordan Ferira, Ph.D., R.D.N. explains further, “Just because vitamin D is fat-soluble by design, doesn’t mean it’s toxic at clinically useful doses, like 5,000 IU. That’s a complete misnomer. In reality, true reports of vitamin D toxicity with clinical evidence have occurred at the 200,000 to 300,000 IU per day—yes, you read that correctly—in vulnerable populations like infants of folks with medical issues.” So, rest assured.