Can Taking Too Much Vitamin D Be Harmful?

Have you been tested for vitamin D recently? Or are you taking a vitamin D supplement?

If so, you should know that according to a recent study, too many people are unnecessarily getting tested for vitamin D deficiency, and millions of people are taking vitamin D supplements in the belief that the vitamin can help with health issues like depression, fatigue, muscle weakness or even heart disease and cancer. 

But researchers don’t have full consensus that vitamin D can prevent or treat any of these conditions. On the other hand, there is evidence to show that taking too much vitamin D can be harmful.

What Is Vitamin D?

Vitamin D is an essential fat-soluble nutrient required by the body for the absorption of calcium and phosphorous, and therefore to build a strong skeleton. The vitamin acts something like a bodyguard, charged with delivering calcium safely to bones and teeth. 

We do not make our own; our bodies produce vitamin D naturally when they are exposed to sunlight. That’s why it’s sometimes called the “sunshine vitamin.”

It’s also found in certain foods, such as fatty fish, cheese, mushrooms, beef liver and egg yolks. Some foods, including milk, cereal, and yogurt, may be fortified with vitamin D.

portobello-mushrooms

Photo Credit: thinkstock

The recommended daily allowance is 600 international units (I.U.) up to age 70, and 800 I.U. for older people.

Why Are So Many People Getting Tested for Vitamin D? 

It 2000, several studies published in medical journals linked vitamin D levels that are lower, but still considered normal, to multiple sclerosis and mental illness, and also to the risk of cancer

Then, in 2007, a paper published in the New England Journal of Medicine stated that vitamin D levels of 21 to 29 nanograms per milliliter of blood, now considered normal, were linked to an increased risk of cancer, autoimmune disease, diabetes, schizophrenia, depression, poor lung capacity and wheezing. 

But over the next few years several research papers decried the exaggerated importance of the vitamin.

In 2016, the New England Journal of Medicine stated:

“The claim that large proportions of North American and other populations are deficient in vitamin D is based on misinterpretation and misapplication of the Institute of Medicine reference values for nutrients — misunderstandings that can adversely affect patient care.” Researchers determined that we are both overscreening for vitamin D deficiency, and unnecessarily treating people who are perfectly healthy.

Nevertheless the belief in the powers of the vitamin has become so popular that increasing numbers of people are asking to be tested for “Vitamin D deficiency,” making it the third-most ordered blood test in the U.S.

In a recent study of 800,000 patients carried out by the Maine Medical Center, around 20 percent had had at least one such test over a three-year period. And according to the Centers for Disease Control and Prevention, the number of these tests among people on Medicare increased 83-fold from 2000 to 2010. Among people with other health insurance, the testing rates went up 2.5-fold between 2009 and 2014.

“A lot of clinicians are acting like there is a pandemic of vitamin D deficiency,” said Dr. JoAnn E. Manson, a preventive medicine researcher at Brigham and Women’s Hospital in Boston, who helped write an Institute of Medicine report on vitamin D. “That gives them justification to screen everyone and get everyone well above what the Institute of Medicine recommends.”

And once they’ve had those tests, there’s another problem, as reported by Gina Kolata writing in The New York Times:

“Labs performing these tests are reporting perfectly normal levels of vitamin D – 20 to 30 nanogram per milliliter of blood – as ‘insufficient.’ As a consequence, millions of healthy people think they have a deficiency.”

Taking Too Much Vitamin D Can Be Dangerous

To remedy their “deficiency”, these people may be taking supplements that are so high, they can be harmful. Vitamin D toxicity is caused by megadoses of vitamin D supplements, not by diet or sunshine: Your body regulates the amount of this vitamin that you need, and even fortified foods contain only small levels of vitamin D.

The chief consequence of these megadoses is a buildup of calcium in your blood, which can cause poor appetite, nausea and vomiting. It can also result in weakness, frequent urination and kidney problems.

So instead of running to the vitamin store when you feel you’re not getting enough vitamin D, why not stock up on foods which are high in the vitamin? Read here for some vegan and non-vegan sources. 

Photo Credit: thinkstock

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