Why and how much vitamin D we need

Get answers to this and other questions about the supplement

Published: April 2013

Most people can get enough vitamin D from moderate exposure to sunlight.

Lots of articles and even some medical professionals have touted vitamin D as the answer to all kinds of health problems and deemed most of us deficient. So taking supplements seems like a no-brainer.

Problem is, many of those claims are overblown. A November 2010 report by the Institute of Medicine (IOM), which examined more than 1,000 studies and other reports, concluded that although vitamin D is essential to bone health, evidence of other benefits was inconclusive.

And what about the "deficiency epidemic"? One explanation is that it blossomed almost overnight when many testing laboratories in this country upped the threshold for what’s considered a normal blood level of vitamin D. "The standards many places are using are somewhat arbitrary and not supported by the evidence," says Clifford Rosen, M.D., of the Maine Cancer Research Institute in Scarborough and a member of the IOM committee. "It’s gotten to the point that nearly 80 percent of people are labeled deficient."

So when it comes to supplements, what makes sense for you? With the help of our medical experts, we waded through the hype to answer four top questions about vitamin D. And if you do need more of the nutrient, our new Ratings of vitamin D supplements has some good news: all contained as much vitamin D as they claimed.

1. Do I need more D?

It depends. It’s a good idea if you don’t get at least some midday sun exposure during the warmer months (the body makes D from exposure to sunlight) or regularly consume vitamin D-rich foods such as fatty fish, eggs, and fortified milk or soy products. In those cases, a vitamin D supplement might help.

Supplements are also recommended for people with osteoporosis (weak bones) or who have a condition, such as celiac disease or Crohn’s disease, that impairs their ability to absorb fat-soluble vitamins.

Being middle-aged or older, dark-skinned, or overweight can slightly increase your risk of deficiency and might tip the balance in favor of taking supplements, particularly if your diet or lifestyle is likely to be "D-ficient."

If you take this supplement, there’s no reason to exceed the recommended intake of 600 IU daily for adults up to age 70; 800 IU for those who are older. "The amount in a multivitamin is typically fine," Rosen advises. But try to avoid exceeding 4,000 IU daily, unless your doctor has prescribed a higher dose to make up for a deficiency. At very high levels, too much D can cause kidney damage. The symptoms of toxicity include nausea, vomiting, poor appetite, constipation, weakness, weight loss, and confusion.

2. Should I get tested?

Not unless you are at risk for deficiency. If you do get tested, keep in mind that vitamin D levels fluctuate with your exposure to sunlight and diet and that results can differ from one laboratory to another. If results are abnormal or unexpected, you should be retested. Results are more likely to be accurate if you use labs that perform high volumes of testing—say, more than 50 vitamin D tests a day.

Although in some labs healthy blood levels of vitamin D are considered to be at least 30 nanograms per milliliter (ng/ml), the IOM says that levels of at least 20 ng/ml are fine to ensure healthy bones. If your levels are well below 20, your doctor will probably recommend a high dose of D for several months followed by a regular supplement thereafter.

3. Do I need to take calcium with my vitamin D?

Yes, unless you meet your recommended calcium intake through your diet. That’s 1,200 milligrams daily for women older than 50 and men older than 70 and 1,000 milligrams for other adults. In most of the clinical trials linking vitamin D supplementation to denser bones or fewer fractures, the nutrient was combined with calcium. The few studies that examined vitamin D alone did not find the same benefits.

3. Does it matter what form of the supplement I take?

No, not really. The D3 form (cholecalciferol) has a reputation for being more potent than D2 (ergocalciferol), but research suggests that’s the case only at high doses. At recommended doses, they work equally well, experts say.

Do kids need vitamin D supplements?

Some do. Because most breast milk does not contain much vitamin D, the American Academy of Pediatrics says breast-fed infants should get 400 IU daily from supplement drops.

To avoid overdose, the Food and Drug Administration says you should use the original dropper that came with the drops, and not to use products in which the dropper is poorly marked or holds more than one drop. For children 1 and older, the recommended vitamin D intake is 600 IU daily. Kids ages 9 to 18 are actively building bone, so it’s critically important for them to get that, as well as their recommended calcium intake of 1,300 milligrams daily.

“Our research shows that adolescent and teen girls are particularly prone to deficiency,” says Dr. Rosen. “So for them, a modest supplement may be good insurance.”

Editor's Note:

A version of this article first appeared in the monthly newsletter Consumer Reports on Health. 

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