All Articles Food Vitamin D studies have their day in the sun, but experts say enthusiasm still outpaces evidence

Vitamin D studies have their day in the sun, but experts say enthusiasm still outpaces evidence

4 min read


It has been two years since the Institute of Medicine released its report on vitamin D that said scientific evidence supported its role in bone health but not much else. It quashed a multitude of early hopes that the sunshine vitamin might prevent cancer and improve health across a variety of medical issues, and for some time afterward, it was relatively quiet on the research front.

A new spate of studies has erupted recently, however, again suggesting vitamin D has a role in preventive and acute health care. A quick search of the SmartBrief archive turned up more than a dozen reports over two months linking vitamin D to strong gums, physical fitness, preventing long hospital stays, tuberculosis, diabetes, colds, prostate cancer, asthma and fractures.

“There were 12 new studies between a Sunday afternoon and Tuesday morning,” Dr. John Cannell, executive director of the Vitamin D Council, told me recently. “We can hardly keep up with it.”

It begs the question: Are we seeing a research breakthrough?

“The enthusiasm for vitamin D is outpacing the evidence,” said Dr. JoAnn Manson, head of the Division of Preventive Medicine at Brigham and Women’s Hospital and professor of medicine at Harvard Medical School. She was on the IOM panel that wrote the 2010 report. “It is very promising, but the evidence at this time is limited.”

Manson said data mostly is coming from observational studies that have substantial limitations, rather than from large, randomized trials. Some of the randomized trials that have been done have shown null or even adverse effects, she said, and added that the low vitamin D dosages used may have affected results.

Blood levels of vitamin D can be confounded by many factors, such as physical activity, poor nutrition and obesity. And Manson cautioned that while studies are promising, “association does not prove causation.”

“JoAnn is exactly right. The enthusiasm is outweighing the science,” Cannell agreed, but quickly ticked off a number of new analyses and randomized controlled trials showing that vitamin D has a role in athletic performance, cancer prevention, and reducing the risk of influenza and maybe even autoimmune diseases.

Low dosages seem to be a big problem for trials. There has been debate over how much vitamin D is too much and the IOM report recommended maximum dosages of between 600 international units and 800 IUs daily. A small study from the University of North Dakota released last month, however, showed no toxicity when people took up to 7,000 IUs per day. Cannell said up to 10,000 IUs per day is safe and the body can make up to 20,000 IUs from a day in the sun.

Cannell said that in general, people need enough vitamin D to reach the natural blood levels humans had when they evolved in East Africa, which they can achieve by getting around 5,000 IU to 7,000 IUs daily.

What is driving the enthusiasm is word of mouth as people try high doses of vitamin D supplements, Cannell said.

“They notice these effects, whether they be that their rheumatoid arthritis goes into remission or their multiple sclerosis seems better or they don’t get as many colds or influenza,” he said. “And they tell their neighbors and their friends. So sales of supplements are skyrocketing.”

On the other hand, he said, physicians must “act on what is now known, not what may be known in the future,” which restricts their vitamin D recommendations to patients.

Moving forward, Manson is lead researcher on what is expected to be a landmark, five-year study on vitamin D. The VITAL study will test 2,000 IUs per day in up to 20,000 people to see if it reduces the risk of cancer and major cardiovascular events.

She said the study is avoiding megadoses of the vitamin to prevent adverse events. It also has ancillary arms that will look at cognitive function, mood, depression, diabetes, blood pressure, autoimmune effects, respiratory infections and cardiac function.