Debating Vitamin D: Leading Docs Still Wrangling On Best Dose For Patients

The message on vitamin D is pretty clear if you talk to Dr. JoAnn E. Manson, M.D., chief of the preventive medicine division at Brigham and Women's Hospital in Boston, who is leading the largest clinical trial in the world investigating the potential health benefits of vitamin D. It boils down to this: Curb Your Enthusiasm. At least for the time being. Even in the midst of a hellish winter when you may be tempted to take an extra dose of the so-called "Sunshine Vitamin" for a boost.

In a commentary piece published this week in the Journal of the American Medical Association, Dr. Manson urges caution. She says that even though the public has become smitten with vitamin D, its growing popularity has led to mega-dosing that's not backed by the current evidence. "More isn't always better, more is sometimes worse," Manson said in an interview. "We don't yet have the answers, so we shouldn't make assumptions." But, she adds, in a couple of years, gold-standard evidence on whether higher doses of vitamin D are good for you should be out.

But get on the phone with Dr. Michael F. Holick, Ph.D., M.D., a leading vitamin D proponent, endocrinologist at Boston Medical Center and professor at Boston University School of Medicine, and you'll get a totally different, but equally clear message. Vitamin D deficiency and insufficiency are far more widespread than certain professional medical groups suggest, Holick says, and dosing at higher levels shows "no evidence of toxicity."

How did we get here and what's a patient to do?

Here's a little background:

In debates over nutrition, vitamin D is one of those supplements that's drawn both passionate supporters and equally aggressive skeptics over the years. And, like coffee, chocolate and red wine, it's often the subject of studies that can make your head spin: it's good for you...until it's not.

The current vitamin D guidelines from the Institute of Medicine recommend 600 IU's per day for adults up to 70 years old and 800 IU's per day for those over 70. "This," writes Manson in her JAMA piece "is equivalent to 3 to 4 daily servings of fortified foods such as milk, yogurt, soy beverages, orange juice, or cereal, plus fatty fish twice per week. These amounts are adequate for at least 97.5% of U.S. and Canadian residents, she says, and it's good even in the bleakest, darkest season, "even if you're in Antartica in winter."

However, she says, the idea that if a little is good then more is better has taken hold among some doctors and patients.

Manson, also a professor at Harvard Medical School, writes: "Many primary care clinicians now include blood tests to measure vitamin D concentrations as part of routine laboratory work and recommend vitamin D supplements, often at high doses, to their patients for the possible prevention of cancer, cardiovascular disease, diabetes, autoimmune disorders, cognitive decline, and other conditions. Thus, screening rates and sales of vitamin D supplements have increased substantially in recent years."

The problem, she says, is that "clinical enthusiasm for supplemental vitamin D has outpaced available evidence on its effectiveness and threatens to jeopardize the ability of researchers to conduct randomized trials in 'usual-risk' populations."

Manson says if you're inclined to take a little extra vitamin D in the winter, say 1000 or even 2000 IU's, that shouldn't be a problem. "We know vitamin D is important for bone health and other health," she says, noting that it's the megadoses of 5000, 6000 or even over 10,000 IU's that are potentially risky. (She points out that the 600-800 IU guidelines are for healthy adults and that for certain patients, there are clear clinical indications for higher doses of vitamin D, for instance people with bone health issues or malabsorption problems.)


There are several large clinical trials currently underway in the U.S., Europe and Australia looking at the health benefits and risks of higher doses of vitamin D. Manson and her colleagues lead the VITamin D and OmegA-3 TriaL (VITAL), the largest randomized trial of vitamin D supplementation in the world with 25,875 men and women). This trial, which should have results by late 2017 or early 2018, is investigating vitamin D supplementation in preventing cancer and cardiovascular disease.

Manson says her JAMA piece is not just about ensuring the integrity of these clinical trials. "If you think this is all about clinical trials, this is not — it's all about what's best for the patient."

She points out that in the past, high doses of certain popular supplements were found to have little or no health benefits and actually pose risks for patients. "Promising preliminary findings were not confirmed when rigorously tested in randomized trials," she writes. "Large trials of other widely used supplements have sometimes found benefits, but in other cases — such as with high doses of beta carotene, vitamin E, and selenium — have disproven some health claims for these supplements and identified health risks that may not have otherwise been detected."

Her basic message is this:

"Avoid going above 4000 IU's a day unless you have a medical condition that warrants this higher dose and that has been established in consultation with a health care provider; and if you're in a trial, you are helping to get answers for future generations, so stick with study guidelines."

Manson and Holick both mention that they're friends, and agree on certain points. But there is a great divide between them when it comes to key points on vitamin D.

I asked Dr. Holick to comment on Manson's piece and this is what he wrote:

Vitamin D deficiency is a significant health problem for children and adults in the United States. The Centers For Disease Control reported that 33% of children and adults are at risk for vitamin D deficiency.

It has been suggested that you can get an adequate amount of vitamin D from dietary sources to satisfy the recommended daily 600 and 800 IUs of vitamin D for adults up to 70 years and above 70 years respectively made by the Institute of Medicine. It was suggested that 3-4 servings of dairy, orange juice, cereals can provide this amount of vitamin D. It cannot. An 8 ounce glass of milk or fortified orange juice contains 100 IUs of vitamin D/8 ounces. Thus a person would need to drink 6-8 glasses of milk or vitamin D fortified orange juice a day to satisfy this requirement. It is essentially impossible to get an adequate amount of vitamin D from dietary sources alone. There is no need to screen everyone for the vitamin D status but rather to prevent vitamin D deficiency everyone should follow the recommendations by the United States Endocrine Society i.e. children less than 1 year 400-1000 IUs daily, children 1 year and older 600-1000 IUs daily and adults 1500-2000 IUs daily. For those who are obese they require 2-3 times more vitamin D. Concerns about vitamin D toxicity are unwarranted based on numerous studies. Adults can take up to at least 10,000 IUs daily and not be concerned about any untoward toxicity. There is no question that vitamin D is critically important for bone health.

There is an avalanche of studies reporting the association with vitamin D deficiency and increased risk for chronic illnesses including heart disease, type 2 diabetes, multiple sclerosis and neurocognitive dysfunction. Therefore based on all of the evidence The Endocrine Society Guidelines recommended that there is no downside to increasing vitamin D intake to their recommended levels.

Source: CDC/National Center for Health Statistics
Source: CDC/National Center for Health Statistics

Readers, how much vitamin D are you taking and whose guidance do you follow on this? Please share here.

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Rachel Zimmerman Reporter
Rachel Zimmerman previously reported on health and the intersection of health and business for WBUR. She is working on a memoir about rebuilding her family after her husband’s suicide. 



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