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.
One way or another, we all eventually learn that 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.
The case study, published in the Canadian Medical Association Journal, explains 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), even though he didn't have vitamin D deficiency and had no history of bone loss, which can be a sign a person isn't getting enough vitamin D. To make things worse, the man took double the amount of vitamin D that the naturopath suggested, which was already way 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 study says that for most people, the daily recommended amount of vitamin D is 400 to 1,000 IU. That number increases to 800 to 2,000 IU for adults at high risk of osteoporosis and for older adults.
The combination of the extreme amount of vitamin D he was consuming and the prolonged sun exposure on his holiday (the skin produces vitamin D after it's exposed to UV light from the sun) caused the man's kidneys to fail. He ended up with a dangerously high amount of calcium in his blood, and his kidneys couldn't filter it properly. He now has chronic kidney disease and may need dialysis in the future.
"Vitamin supplements are meant to fill a gap or provide an optimal amount that can't be reached by food alone," says Cynthia Sass, RD, Health contributing nutrition editor. 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 showed us, it could actually be dangerous.
Any vitamin taken in excess can be harmful, though different vitamins will have different effects on the body if misused. For example, too much vitamin C can cause diarrhea, while too much vitamin B6 can lead to nerve damage. "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," says Sass.
Before taking a vitamin supplement, first consult a nutritionist or physician. Sass says 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, tells 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 physician may recommend taking over 100%, but that's a decision that should be made by a professional.
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 says.