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For most people, a daily dose of 400 to 1,000 international units of vitamin D is sufficient. Getty Images

Doctors are warning patients to be cautious about the amount of vitamin D supplements they take after a man developed kidney damage due to excess dosages.

The 54-year-old man showed increased levels of creatine in his blood, suggestive of kidney damage and malfunction. Upon referral to a kidney specialist and further tests, doctors found the man had been prescribed a high dosage of vitamin D by a naturopath.

The naturopath had advised the man to take eight drops of vitamin D daily. Over a period of more than two years, the man consumed between 8,000 and 12,000 international units (IU) of vitamin D daily.

The recommended daily amount for the average person is between 400 and 1,000 IU.

Due to the high amount of vitamin D the man was taking, he had an excessive amount of calcium in his blood, which led to kidney damage.

“It was surprising to see the degree of kidney function he had lost suddenly almost to the point of requiring dialysis,” Dr. Bourne Auguste, a clinical fellow in home dialysis at Toronto General Hospital and the University of Toronto, told Healthline.

“Vitamin D toxicity had been previously reported in the medical literature but has been exceedingly rare,” he said. “The main surprising element was that this patient was taking as much vitamin D as possible to strengthen the bones but was not aware that there was a risk of toxicity with extremely large doses.

“Kidney failure is not reversible. In this case, this patient is now left with 30 to 35 percent kidney function. Previously before this vitamin D exposure, his function was greater than 70 percent.

“Patients with progressive kidney failure and usually with less than 10 to 15 percent function usually need dialysis to clear toxins from the body. This patient has an extremely high risk of needing dialysis at some point in his life. His kidney failure resulted from the high calcium levels in the blood, with calcium depositing in various parts of the kidney causing damage,” Auguste explained.

Vitamin D plays an important role in helping the body build strong bones.

It enables the body to absorb adequate levels of calcium and phosphate, which keep bones healthy.

The average person gets most of their vitamin D from sunlight, although fortified foods, such as milk and cereals, can also provide vitamin D.

According to the Mayo Clinic, most American adults get enough vitamin D without supplementation. Yet more and more people are taking supplements.

In the case of the 54-year-old man, the naturopath had prescribed high doses of vitamin D despite the man not having a history of vitamin D deficiency or bone loss.

It’s a trend that Dr. Sterling Ransone, Jr., a director at the American Academy of Family Physicians, says is becoming all too common.

“Unfortunately many people equate vitamins and ‘natural’ products with safety… Unfortunately, that’s not the case, and you can very easily get too much of these things. Particularly the fat-soluble vitamins, vitamins A, D, E and K,” Ransone told Healthline.

“If you’d asked me eight years ago, I would have told you they absolutely were necessary,” he added. “(But) over the last year or two, the studies that have come back really have not shown benefit from doing supplemental vitamin D.”

Taking too much vitamin D can cause problems such as constipation and nausea and, in more serious cases, kidney stones and kidney damage.

Vitamin D supplementation is a controversial topic. The experts who spoke with Healthline held varying views on whether supplementation was necessary.

Dr. Zhaoping Li, director of the UCLA Center for Human Nutrition, is in favor of vitamin D supplementation — as long as it’s done safely under guidance from a physician.

“Vitamin D supplementation is important for most of us, as long as we take it responsibly. Side effects are very rare. There is a trend, supported by evidence, to recommended vitamin D supplementation, but that does not mean the more the merrier,” she told Healthline.

Many of the experts who spoke with Healthline noted a trend toward people believing vitamins, supplements, or “natural” treatments are safe and therefore can be taken in high doses.

“There seems to be a belief that if a little is good, more must be better, which can cause problems and side effects, as in this case,” Dr. Stephen Bent, a professor of medicine, epidemiology, and biostatistics at the University of California, San Francisco, told Healthline.

But Bent says recent research has shown higher levels don’t necessarily equate to improved health outcomes.

He notes a randomized controlled trial published this year called the VITAL study that randomly assigned a large group of adults to either a placebo or 2,000 IU of vitamin D per day.

“The study was focused on cardiovascular outcomes like heart attack and stroke and cancer, and it found no benefit from vitamin D compared to placebo,” Bent said.

“So, at least in these doses (more than twice the Institute of Medicine recommendation), there appears to be no additional health benefit. Some people still believe that even higher doses, 5,000 or 10,000 IU, may lead to some benefits, but this is not scientifically proven,” he added.

Recommendations for safe daily doses of vitamin D range from 400 to 1,000 IU per day to up to 2,000 IU per day.

Auguste says a patient is unlikely to develop toxicity, as experienced by the 54-year-old man, if they’re taking less than 4,000 IU daily. But that doesn’t mean vitamin D needs to be taken.

“Not everyone needs to be on vitamin D, let alone large doses. The take-home message is that taking large doses of vitamin D does not necessarily equate to more benefit. It can lead to significant harm, and patients along with practitioners should have an increased awareness of its risk,” Auguste said.