Taking vitamin D supplements may help stave off psoriasis, rheumatoid arthritis, lupus and other autoimmune diseases, a new study suggests.
Previous research has hinted at this connection, but the new study is the first randomized controlled trial to look at what happens when people are given vitamin D supplements and followed to see if they develop an autoimmune disease, the study authors said. Randomized controlled trials are considered the gold standard in clinical research.
In the new study, people who took 2,000 international units per day (IU/day) of vitamin D, with or without one gram of fish oil, for slightly more than five years reduced their risk of developing an autoimmune disease by 22% when compared to their counterparts who took placebo ("dummy") pills.
"It looks like giving vitamin D will prevent autoimmune disease, which is really exciting," said study author Dr. Karen Costenbader, a rheumatologist at Brigham and Women's Hospital in Boston.
There's no shortage of mechanisms to explain this finding. "Vitamin D binds to receptors on immune system cells to turn on an array of genes involved in immune system function," she said.
Autoimmune diseases occur when your immune system engages in destructive "friendly fire" against its own body parts.
Vitamin D is called the "sunshine vitamin" because our bodies produce it when exposed to sunlight. It is hard to get as much as we need from food, so most people will need supplements. The Institute of Medicine recommends people aged 1 to 70 take 600 IU/day and that adults older than 70 aim for 800 IU/day. Other medical groups set the bar even higher.
The new study, dubbed the Vitamin D and Omega-3 Trial (VITAL), included close to 26,000 adults (aged 67, on average). These folks were not vitamin D deficient and weren't considered high risk for developing autoimmune diseases.
Participants were randomly assigned to receive either 2,000 IU/day of vitamin D with a 1 gram omega-3 fatty acid supplement; vitamin D with a placebo; omega-3 fatty acid with a placebo; or placebo alone. The participants then answered questionnaires about new diagnoses of autoimmune diseases, and doctors reviewed their records to confirm these diagnoses.
People who took vitamin D or vitamin D and omega-3 fatty acids had a lower rate of autoimmune disease than people who took a placebo or omega-3 fatty acids alone after slightly more than five years of follow-up, and these effects were more pronounced after two years.
Omega-3 fatty acids alone didn't significantly lower the incidence of autoimmune disease. Many autoimmune diseases are marked by inflammation, and fish oil is known to help cool inflammation.
Costenbader and colleagues plan to continue to follow participants for a few more years. "We want to see who benefits the most in terms of which autoimmune diseases were prevented and whether vitamin D works as well or better in people who are at high risk for autoimmune disease," she noted.
This is important as there are more than 80 autoimmune diseases, she explained.
Vitamin D and fish oil are safe, Costenbader said. "I suggest vitamin D 2,000 IU/day and 1 g/day of marine omega-3 fatty acids (fish oil) — the same doses used in VITAL," she added.
You can get all of the vitamin D you need by spending 15 minutes in the sun every day. But "this is tricky as a lot of sun exposure leads to skin cancer," she said.
Still, Costenbader cautioned not everyone should jump on the vitamin D supplement bandwagon. "There are some people who need to avoid vitamin D because they have a history of kidney stones or other diseases," she said. "Check with your doctor before you start taking supplements."
VITAL was designed to see if vitamin D could reduce the risk of developing cancer, heart disease and stroke. The risk for developing autoimmune disease was another endpoint in this trial.
The report was published online Jan. 26 in the BMJ.
Dr. Michael Holick has devoted his career to studying vitamin D. He's a professor of medicine, physiology, biophysics and molecular medicine at Boston University School of Medicine.
"There's a lot of evidence suggesting that vitamin D would help to reduce the risk for autoimmune disease, and this study confirms that vitamin D status, even if you are vitamin D sufficient, is associated with decreased risk for developing autoimmune diseases," said Holick, who has no ties to the new research.
This makes sense, he said: "Vitamin D is a major modulator of immune function at every level."
There's no downside to increasing your vitamin D intake, and there's a whole lot of upside, he said. Studies have linked vitamin D deficiency to a host of diseases and conditions including heart disease, diabetes, the brittle bone disease osteoporosis, certain types of cancer and depression.