Is Vitamin D Dangerous?


by Carole Jackson, Bottom Line Health

Slam on the brakes — after several years of exuberance about vitamin D as the magic solution for everything from preventing cancer to curing depression, the Institute of Medicine has just issued cautionary advice about taking too much of the sunshine vitamin. I’m glad to see it — I’ve come across reports from organizations such as the Vitamin D Council and Livestrong suggesting that consumers consider taking 5,000 international units (IU) or more of vitamin D per day — and, as this report makes clear, that’s a potentially dangerous dose. I called Alan Gaby, MD, author of the just published book Nutritional Medicine ( for some expert insights on the appropriate use of vitamin D for good health.

Where “D” Advice Went Wrong

How did this situation reach such extremes? As it happens, there were some very good reasons why scientists got concerned about plummeting levels of vitamin D among Americans. Changes in lifestyle, including the fact that people were spending more and more time indoors, plus slathering on sunscreen and practicing other sun-avoidance techniques, resulted in widespread deficiency of this important nutrient. That’s a problem, since vitamin D is vital to good health.

A refresher: Vitamin D is actually a type of “pre-hormone” that the body converts into a hormone that regulates as many as 1,000 different genes. Among its many protective functions, D helps eliminate precancerous cells… prevent cardiac disease, stroke and diabetes… maintain the immune system and thus protect against colds, flu and the like… protect joints against arthritis… and promote absorption of calcium and phosphate, making it vital for healthy bones and teeth. Some of the problems caused or exacerbated by low levels of vitamin D include muscle weakness, poor balance leading to recurrent falls, low back pain and osteoporosis. A lack of D also can make fibromyalgia worse, says Dr. Gaby. Given that long list, it’s no wonder that excitement about vitamin D became so intense.

How Much — and Too Much

Until a few months ago, the standard recommendation from the Institute of Medicine for vitamin D intake for adults age 51 to 70 had been 400 IU/day… and for adults over age 70, it was 600 IU/day. That was definitely not enough, Dr. Gaby said — evidence shows that people under age 70 need 600 IU/day and adults over age 70 need 800 IU/day to prevent falls and thinning bones, which is what the new Institute of Medicine report recommends.

Although some scientists and doctors believe that people should routinely take larger doses, Dr. Gaby said research doesn’t support this. “Given the weakness of the evidence regarding both safety and efficacy, I think that caution is in order,” he said, adding that he personally does not recommend doses above 2,000 IU per day except in rare circumstances. “I am not anti-vitamin D, but it is premature and potentially dangerous to take large doses for the sole purpose of pushing blood levels to an arbitrary target level,” he said.

Dr. Gaby said it is important to realize that too much D is toxic and can cause serious problems, including a buildup of calcium in the blood (hypercalcemia) that can result in nausea, vomiting, weakness, constipation, heart rhythm abnormalities and possibly kidney stones. Another serious concern is atherosclerosis (hardening of the arteries) — one study showed that swine fed high doses of vitamin D-3 developed arterial changes akin to those seen in people who need coronary bypass surgery.

It’s Complicated

Vitamin D is a uniquely complex nutrient, Dr. Gaby noted — maintaining the right levels to optimize health isn’t a simple matter of swallowing a supplement once or twice a day. Specifically, he cited the following challenges:

  • Our bodies manufacture Vitamin D in response to sunlight. The biochemical effects of sunlight exposure are not the same as what occurs with oral supplementation with D. So-called “sunshine D” has built-in protection against toxicity as it prevents the release of excessive amounts into circulation and also modulates how it is used in the body.
  • Testing for D is imprecise and not always reliable. The most common blood test to measure D levels is called the 25(OH)D, which shows levels based on intake and sun exposure over three weeks. However, genetic differences can intrude on this test’s accuracy, Dr. Gaby said.
  • It’s hard to get significant amounts of vitamin D from foods, even fortified ones.

What to Do About D

For those reasons, it’s good to get vitamin D the old-fashioned way — spend 10 to 15 minutes in the sun most days during the hours from 10 am to 2 pm. Expose as much skin as possible and, do not wear any sunscreen during this time.

Dr. Gaby said that most people would do well to take 800 IU to 1,200 IU of D-3 each day, especially during the winter months and most especially for people who are seldom in midday sun and older adults, whose skin loses some of its ability to manufacture D from sunlight. But, said Dr. Gaby, people with osteoporosis and diseases that cause malabsorption (such as Crohn’s disease) should probably be tested to determine where they are in terms of D levels, since they may require supplementation in higher doses.

While vitamin D is not the magic bullet some experts have made it out to be, it is without question immensely important. Do make an effort to get regular doses from sunlight, food and supplements… but do not overdo your D!


Alan Gaby, MD, author of Nutritional Medicine (self-published, available at He is a past president of the American Holistic Medical Association, testified before the White House Commission on Complementary and Alternative Medicine, and is the contributing medical editor of the Townsend Letter. He is based in Concord, New Hampshire.