By Gina Kolata (International New York Times)
NEW YORK April 12: 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 2000-10, according to the Centres for Disease Control and Prevention. Among patients with commercial insurance, testing rates rose 2.5-fold from 2009-14.
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 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 randomised trials had found no particular benefit for healthy people to have blood levels above 20 nanograms per mililitre.
Medical organisations, 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 Rosen, an osteoporosis researcher at the Maine Medical Centre Research Institute and a member of the Institute of Medicine’s committee.
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 synthesise 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 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 IU 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.
A 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 mililitre 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 mili litre, which meant that most people were vitamin D deficient.
The group recommended taking supplements but not widespread testing, on the grounds that this would not be cost-effective.
The new guideline had an immediate effect: Commercial labs began describing levels of 20 to 30 nanograms per mili litre as insufficient. Many continue to do so today.
“There was a vitamin D bandwagon,” said Dr Sundeep Khosla, an osteoporosis expert at the Mayo Clinic. Vitamin D tests “became incorporated into the general evaluation of patients,” he added.
Ravinder J Singh, who runs a testing lab at the Mayo Clinic, was taken aback by the sudden deluge. “Demand for vitamin D testing went through the sky,” he said.
“It was almost as though there was nothing else serious in clinical practice.” Fairfield, like many other general practitioners, began testing patients, trying to make sure they raised their vitamin D levels above 29 and became concerned that she and other doctors had been too cavalier about the vitamin.
“We were worried that there was a lot we were missing,” she said.
But when the Institute of Medicine report proved critical of the vitamin D craze, she started telling healthy patients there was no reason for them to be tested.
Many did not want to hear that advice. “People were used to vitamin D monitoring, like with cholesterol,” Fairfield said. “They wanted to know what their number is.”