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1 Question, 5 Answers: What’s the Deal With Vitamin D?

Kelsey Tyler

There’s no question that you need vitamin D, which helps your body absorb calcium. Vitamin D deficiency can lead to bone loss and an increased risk of fractures. But determining whether someone is getting enough vitamin D from sun exposure and diet alone, or if they need supplements to boost their levels, is less clear-cut. In fact, vitamin D deficiency is a subject of heated debate in the medical community. Experts have taken issue with everything from what constitutes a deficiency to whether vitamin D testing should be part of routine care to how beneficial supplements truly are. Despite this, not all doctors believe vitamin D is being overhyped.

We asked five physicians and medical researchers what patients should know about being labeled as vitamin D deficient and taking daily sunshine supplements.


JoAnn Manson

Professor of medicine, Harvard Medical School, and lead researcher for a study on vitamin D supplements
MD, MPH, DrPH

Our study on vitamin D tested 26,000 men and women 50 and older who took 2,000 IUs vitamin D3 supplements daily to determine whether supplementation reduces the risk of cancer or cardiovascular disease. We did not find an association between taking supplements with fewer incidences of cancer or cardiovascular events, but we also did not identify any adverse reactions.

If you’re already taking these supplements, we didn’t find clear reasons for stopping — there are no risks of increased side effects. But we caution against mega-dosing, [which means] anything more than 4,000 IUs daily.

As for testing, we only recommend it for patients with bone health problems; those with malabsorption problems due to colitis, Crohn’s, anti-seizure medication or tuberculosis medication; and certain patients with low dietary intake and who get virtually no sunlight — like those in institutions. Even people in northern latitudes in winter get enough sunlight to meet their vitamin D needs.


Alison Avenell

Clinical nutritionist at the University of Aberdeen and co-author of a study on the efficacy of vitamin D supplementation on bone density, U.K.
MD

The only group that should take vitamin D supplements are people who are housebound and never get out in the light or who cover themselves up when they are outside. These people, particularly children, could develop vitamin D deficiency and rickets. But incidents of children experiencing rickets are very rare.

The prevalence of people with low vitamin D levels — less than 25 nanograms per milliliter (ng/mL) — is really pretty low. For most people, there is no benefit in supplementation. There is no marked harm associated with low-dose supplements of vitamin D, but there is also no benefit.

Lab testing for vitamin D levels in the blood is imprecise, not very reliable and difficult to interpret. Sun exposure that boosts vitamin D can affect measurements for up to two years, for example. But demand for vitamin D testing has gone through the roof and has become a burden on the healthcare system in the U.K., at least. Each screening test costs $30 to $35.

The most reliable predictors for vitamin D deficiency are lack of sunlight year-round and a diet low in vitamin D — so a diet lacking in fortified foods, eggs, oily and fatty fish and vitamin D milk.


Joel Fuhrman

Author, Eat to Live, and nutritional researcher
MD

When you read about vitamin D, you need to discount any vitamin D2 studies. Some medical studies look at vitamin D2 at excessively high doses and show unfavorable outcomes. It’s vitamin D3 that can help protect against certain types of cancer and osteoporosis, and which is associated with longer lifespans.

Vitamin D is the sunshine vitamin, but going outside may not be enough. You need sun exposure on your arms and legs, not just on your face. Many people in regions of the U.S. and Canada don’t have enough access to sun exposure all year, so judicious use of D3 is a reasonable thing to do. Testing your blood with the hydroxy-25 vitamin D test is also reasonable to assure your level is above 25 ng/mL.   

If you’re not taking 1000 – 2,000 IUs a day then it can be important to get your vitamin D levels tested. Potential deficiency is risky and shouldn’t be ignored.


Samantha Kimball

Professor at St. Mary’s University and scientific advisor for the Vitamin D Society, a nonprofit group organized to increase awareness of health conditions linked to vitamin D deficiency, Calgary
PhD

The immune system is dependent on vitamin D, and optimal vitamin D levels are not just what’s optimal for bone health. Vitamin D is used by just about every cell in the body, and symptoms of lowered levels are unrecognizable as vitamin D deficiency alone.

In Canada, it’s assumed most people are vitamin D–deficient — and by that I mean not at optimal levels for various health outcomes. I recommend 1,000 IU vitamin D supplements daily, either as tablets, capsules or drops. Most people need 1,000 to 4,000 IUs daily, but many factors impact that requirement — weight, age, sex and the presence of gastrointestinal disorders all affect absorption.


Paul Hyman

Pediatrician, Topsham, Maine
MD

I tell my patients that vitamin D supplements are relatively safe at normal doses but can be dangerous at high levels. Vitamin D was oversold as the next big thing and has now come back down to earth, but many people don’t get enough. The Institute of Medicine set levels to close to 20 ng/mL, but bone metabolism specialists often shoot for levels closer to 40 ng/mL, which is what I advise for patients with osteoporosis.

Vitamin D is a well-known example of over-testing, but it is still recommended to test people with certain diseases such as celiac, osteopenia and osteoporosis, and those who have had bariatric surgery. Obesity is also a risk factor for low vitamin D.

I know the USPSTF [an independent, volunteer panel of experts in disease prevention and evidence-based medicine] does not recommend routine screening. In addition to it not being clinically indicated, there is the practical matter that most insurances don’t pay for a screening vitamin D test, so patients foot the bill.


Responses have been condensed and lightly edited.

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