Low Vitamin D Levels Linked to Disease in Two Big Studies
Lawrence Lool/European Pressphoto Agency
New research has found that lower vitamin D levels were associated with illness, but didn’t show whether they were a cause.
People with low vitamin D levels are more likely to die from cancer and heart disease and to suffer from other illnesses, scientists reported in two large studies published on Tuesday.
The new research suggests strongly that blood
levels of vitamin D are a good barometer of overall health. But it does
not resolve the question of whether low levels are a cause of disease
or simply an indicator of behaviors that contribute to poor health, like
a sedentary lifestyle, smoking and a diet heavy in processed and
unhealthful foods.
Nicknamed the sunshine nutrient, vitamin D is
produced in the body when the skin is exposed to sunlight. It can be
obtained from a small assortment of foods, including fish, eggs,
fortified dairy products and organ meats. And blood levels of it can be
lowered by smoking, obesity and inflammation.
Vitamin D helps the body absorb calcium
and is an important part of the immune system. Receptors for the
vitamin and related enzymes are found throughout cells and tissues of
the body, suggesting it may be vital to many physiological functions,
said Dr. Oscar H. Franco, a professor of preventive medicine at Erasmus Medical Center in the Netherlands and an author of one of the new studies, which appeared in the journal BMJ.
“It has effects at the genetic level, and it
affects cardiovascular health and bone health,” he said. “There are
different hypotheses for the factors that vitamin D regulates, from
genes to inflammation. That’s the reason vitamin D seems so promising.”
The two studies were meta-analyses that
included data on more than a million people. They included observational
findings on the relationship between disease and blood levels of
vitamin D. The researchers also reviewed evidence from randomized
controlled trials — the gold standard in scientific research — that
assessed whether taking vitamin D daily was beneficial.
Dr. Franco and his co-authors — a team of
scientists at Harvard, Oxford and other universities — found persuasive
evidence that vitamin D protects against major diseases. Adults with
lower levels of the vitamin in their systems had a 35 percent increased
risk of death from heart disease, 14 percent greater likelihood of death
from cancer, and a greater mortality risk overall.
When the researchers looked at supplement
use, they found no benefit to taking one form of the vitamin, D2. But
middle-aged and older adults who took another form, vitamin D3 — which
is the type found in fish and dairy products and produced in response to
sunlight — had an 11 percent reduction in mortality from all causes,
compared to adults who did not. In the United States and Europe, it is
estimated that more than two-thirds of the population is deficient in
vitamin D. In their paper, Dr. Franco and his colleagues calculated that
roughly 13 percent of all deaths in the United States, and 9 percent in
Europe, could be attributed to low vitamin D levels.
“We are talking about a large part of the
population being affected by this,” he said. “Vitamin D could be a good
route to prevent mortality from cardiovascular disease and other causes
of mortality.”
In the second study, also published in BMJ, a team of researchers at Stanford and several universities in Europe presented a more nuanced view of vitamin D.
They concluded there was “suggestive evidence” that high vitamin D levels protect against diabetes, stroke, hypertension
and a host of other illnesses. But they also said there was no “highly
convincing” evidence that vitamin D pills affected any of the outcomes
they examined.
“Based on what we found, we cannot recommend
widespread supplementation,” said Evropi Theodoratou, an author of the
study and research fellow at the Center for Population Health Sciences
at the University of Edinburgh. The second study also looked at bone
health. While Vitamin D had long been believed to help prevent osteoporosis fractures from falls, clinical trials in recent years have challenged the idea. The study also found no evidence to support that assumption.
“Vitamin D might not be as essential as
previously thought in maintaining bone mineral density,” Dr. Theodoratou
and her colleagues wrote.
Dr. Theodoratou was not alone in suggesting
people hold off on taking vitamin D supplements for now. Even though Dr.
Franco found them to be beneficial, he said that more research was
needed to show what levels are best. Instead of taking pills, people
could improve their vitamin D levels with an adequate diet and 30
minutes of sunlight twice a week, he said.
“The most important factors in obtaining
vitamin D are going out and doing some exercise and following a healthy
diet,” he added.
And in an editorial that accompanied the studies
in BMJ, Paul Welsh and Dr. Naveed Sattar of the British Heart
Foundation’s Glasgow Cardiovascular Research Center pointed out that
previous research “extolled the virtues of antioxidant vitamins only for major trials of vitamins E and C and beta carotene to show null, or even some harmful, effects of supplementation.”
They said vitamin D pills should not be
recommended widely until clinical trials that are underway shed more
light on the benefits and potential side effects.
But Duffy MacKay, a spokesman for the Council for Responsible Nutrition,
a supplement industry trade group, said that vitamin D is not easily
obtained through food alone, and noted that exposure to sunlight has its
dangers.
He said he agreed with Dr. Franco that more research was needed to identify “an optimal dose and duration” of vitamin D.
“But there is enough positive research
currently to indicate that people should be supplementing with vitamin D
for a variety of positive health outcomes,” he added.
This post has been revised to reflect the following correction:
Correction: April 5, 2014
An earlier version of this article incorrectly listed kale as a source of vitamin D. It is not.
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