Is Too Much Vitamin D Bad for You? We Asked Nutritionists for the Facts

A Canadian man's kidneys failed after he took too much vitamin D. Here's why.

Sometimes you really can have too much of a good thing. A Canadian man learned that lesson the hard way: For more than two years, he regularly took an extremely high dose of vitamin D—which unfortunately caused permanent damage to his kidneys.

A 2019 case report, published in the Canadian Medical Association Journal, explained that the 54-year-old went to his family physician after returning from a trip to Southeast Asia, where he spent pretty much all day, every day sunbathing. His physician found increased levels of creatinine in his blood, a sign that his kidneys, which usually filter out excess creatinine, were malfunctioning. His physician urgently referred him to a specialist.

Only then did doctors learn that the man had been prescribed high doses of vitamin D by a naturopath (a practitioner who focuses on natural remedies and alternative medicine). Prior to taking the supplements, the man didn't have any signs of vitamin D deficiency, such as a history of bone loss. To make things worse, the man took double the amount of vitamin D that the naturopath suggested, which was already too high to begin with.

Every day for over two and half years, the man took eight to 12 drops of vitamin D, totaling 8,000 to 12,000 International Units (IU). The National Institute of Health (NIH) says that for most adults between the ages of 51 to 70, the daily recommended amount of vitamin D is 600 IU, with an upper limit of 4000 IU.

According to a 2016 review article published in Endocrine Reviews, excess vitamin D leads to toxic amounts of calcium —which can damage the kidneys.

According to the case report, sun exposure helps the body produce the active form of vitamin D. And the case report went on to explain that the combination of high vitamin D consumption with prolonged sun exposure on the patient's holiday led to his kidney failure. He ended up with a dangerously high amount of calcium in his blood, and his kidneys couldn't filter it properly.

At the time of the case report, the patient was diagnosed with chronic kidney disease and was told that he might eventually need dialysis.

Vitamin Supplementation Safety

Any vitamin taken in excess can be harmful, though different vitamins will have different effects on the body if misused. "The surplus can build up in the body and damage various organs or systems, throw the body out of balance, or stress organs that are involved with trying to purge the excess," said Cynthia Sass, RD, Health contributing nutrition editor.

For example, according to a 2019 review in Canadian Science Publishing, too much vitamin C can cause diarrhea, too much vitamin B6 can lead to nerve damage, too much magnesium can cause muscle paralysis, and too much iron can cause abdominal distress. The review also found that patients who take multiple supplements have a higher risk of inadvertently taking too much.

Before taking a vitamin supplement, first consult a nutritionist or healthcare provider. Sass explained that they will "assess your diet and possibly [do] blood work to determine if a supplement is needed, identify an ideal dose, and determine the length of time the supplement should be taken."

Julie Upton, RD, told Health it's also important to read the nutrition label when buying a supplement. Look for the "% Daily Value." If it's above 100%, the amount is more than your body needs. Of course, in some cases, a nutritionist or healthcare provider may recommend taking more than 100%, but that's a decision that should be made by a professional.

Getting Vitamin D In Your Diet

"Vitamin supplements are meant to fill a gap or provide an optimal amount that can't be reached by food alone," explained Sass. Basically, if you're not deficient in a vitamin, taking it in a supplement won't improve your health in any way. In fact, as this case report showed us, it could actually be dangerous.

And remember, your diet could very well be providing all of the vitamins you need already. "If you focus on a balanced diet with plenty of fruits, veggies, whole grains, lean protein, and healthy fats, it is highly unlikely you would have any nutritional deficiencies," Upton advised.

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