All that vitamin D we’re taking? There’s little evidence to justify it – The San Diego Union-Tribune
There was no reason for the patients to receive vitamin D tests. They did not have osteoporosis. Their bones were not cracking from a lack of the vitamin. They did not have diseases that interfere with vitamin D absorption.
Yet in a recent sample of 800,000 patients in Maine, nearly one in five had had at least one test for blood levels of the vitamin over a three-year period. More than a third got two or more tests, often to evaluate such ill-defined complaints as malaise or fatigue.
The researchers who gathered the data, Dr. Kathleen Fairfield and Kim Murray of the Maine Medical Center, were surprised. Perhaps they shouldn’t have been.
Millions of people are popping supplements in the belief that vitamin D can help turn back depression, fatigue, muscle weakness, even heart disease or cancer. In fact, there has never been widely accepted evidence that vitamin D is helpful in preventing or treating any of those conditions.
But so firm is this belief that vitamin D has become popular even among people with no particular medical complaints or disease risks. And they are being tested for vitamin D “deficiency” in ever greater numbers.
The number of blood tests for vitamin D levels among Medicare beneficiaries, mostly people 65 and older, increased 83-fold from 2000 to 2010, according to the Centers for Disease Control and Prevention. Among patients with commercial insurance, testing rates rose 2.5-fold from 2009 to 2014.
Labs performing these tests are reporting perfectly normal levels of vitamin D — 20 to 30 nanograms per milliliter of blood — as “insufficient.” As a consequence, millions of healthy people think they have a deficiency, and some are taking supplemental doses so high they can be dangerous, causing poor appetite, nausea and vomiting.
Vitamin D overdoses also can lead to weakness, frequent urination and kidney problems.
“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.”
In fact, the institute committee on which Manson served concluded in 2010 that very few people were vitamin D deficient and noted that randomized trials had found no particular benefit for healthy people to have blood levels above 20 nanograms per milliliter.
Medical organizations, too, have repeatedly found that there is no reason to assess vitamin D levels in healthy adults, and recently two rigorous studies failed to find that high doses of the vitamin protect against heart disease or cancer.
Still, vitamin D has become “a religion,” said Dr. Clifford J. Rosen, an osteoporosis researcher at the Maine Medical Center Research Institute and a member of the Institute of Medicine’s committee.
Made in sunlight
Vitamin D is a fat-soluble nutrient needed to absorb calcium and phosphorus, and therefore to make bones strong. People do not make their own: We need sunlight to synthesize vitamin D. The vitamin also is found in oily fish and in a few other foods, including milk, which is fortified with the vitamin.
Because many people have little exposure to sunlight, especially those living in northern climates in winter, some investigators became concerned more than a decade ago that large swaths of the population were not getting enough vitamin D.
One is Dr. Michael F. Holick, a professor of medicine, physiology and biophysics at Boston University School of Medicine and a leading proponent of the idea that just about everyone needs a vitamin D supplement.
He points to studies that suggest an association between low vitamin D levels and higher rates of various diseases. While these observational reports do not prove cause and effect, he is persuaded by the fact that many point in the same direction, hinting that low blood levels of vitamin D are hazardous.
Doctors, he believes, must take action.
The recommended daily allowance is 600 international units up to age 70, and 800 I.U. for people who are older, Holick said.
Diet cannot provide that much of the vitamin, he notes. And it would require nearly constant exposure to sunlight to reach the levels he recommends.
Over the years, he acknowledged, studies in which people were randomly assigned to take a vitamin D pill or a placebo have failed to support claims for the vitamin’s benefits. But those studies tended to be too small to be definitive, he said.Yet recent trials, larger and more rigorous, also have not produced the hoped-for results.
One study with 5,108 participants, published this month in JAMA Cardiology, found that vitamin D did not prevent heart attacks.
Another study, published at the end of March, included 2,303 healthy postmenopausal women randomly assigned to take vitamin D and calcium supplements or a placebo. The supplements did not protect the women against cancer, the researchers concluded.Other, more ambitious studies are underway, including a five-year randomized study of almost 26,000 healthy men and women directed by Manson and Julie Buring, who hope to answer once and for all whether taking vitamin D can prevent cancer, heart disease and strokes.
Parade of papers
The frenzy for vitamin D began not in natural food stores but in medical journals. Beginning around 2000, a series of research papers linked vitamin D levels that are lower, but considered normal, to multiple sclerosis and mental illness, then to cancer risk and bone health.
Blood testing for the vitamin took off. “Patients began asking for it,” said Fairfield, the researcher in Maine. “A lot of people thought that if they were fatigued or sad or they did not feel well, they might be vitamin D deficient.”
In 2007, Holick published a paper in The New England Journal of Medicine asserting that vitamin D levels now considered normal — 21 to 29 nanograms per milliliter of blood — were linked to an increased risk of cancer, autoimmune disease, diabetes, schizophrenia, depression, poor lung capacity and wheezing.
He also published books promoting the idea that vitamin D levels in that range were insufficient to promote good health.
In 2011, a committee of the Endocrine Society, headed by Holick, came out with a recommendation that vitamin D levels be at least 30 nanograms per milliliter, which meant that most people were vitamin D deficient.
The group recommended the taking of supplements but not widespread testing, on the grounds that this would not be cost-effective.