If you want to start a fight at a medical conference, the triggers are simple: Vitamin D and fish oil are all you need to get those feisty scientists’ blood pressure up. These extremely popular supplements are a cash cow (the supplement industry is worth over $1 billion) but scientists are yet to parse out who — if anyone — might benefit from taking them. They also don’t really know what the benefits of these supplements are for the body and brain, despite what the label may be promising you. But they are getting there: A new study suggests Vitamin D supplements may be linked to a positive immune effect.

What’s new — A new data analysis published in The British Medical Journal suggests people who take Vitamin D regularly are less likely than those who don’t to develop autoimmune diseases. Autoimmune conditions like lupus or rheumatoid arthritis arise when the body’s own immune system goes rogue and attacks healthy tissues.

The same analysis found less clear links between taking fish oil supplements and autoimmune conditions, but the results here are a little more complicated.

Vitamin D is the most popular supplement in the U.S. while fish oil (or, more officially, marine omega 3 fatty acid supplementation) is the third most popular supplement, according to one recent market study. Yet scientists know surprisingly little about what they actually do to benefit our bodies or brains.

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Vitamin D supplements can help many people who don’t get enough of the vitamin from their food or sunlight. Too little vitamin D can jeopardizes bone and dental health. Some scientists are also becoming increasingly convinced that vitamin D does more than help the body to absorb calcium.

There’s evidence to suggest vitamin D has benefits for cognitive and cardiovascular health, and it may play a role in the immune system.

Fish oil, meanwhile, has been shown to lower cholesterol, reduce arthritis, and alleviate ADHD symptoms. There’s also research hinting it reduces inflammation. But the data so far are not overwhelmingly conclusive.

Testament to how many times researchers have tested vitamin D and fish oil for various medical uses are the lengthy fact sheets from the National Institutes of Health’s Office of Dietary Supplements. Yet most of the evidence falls short of the NIH’s standard for recommending a supplement for any particular use beyond those established above. The new analysis, however, hints at a different benefit.

Science in Action — The data in the new study stems from a trove of health information and research gathered as part of the VITAL (Vitamin and Omega 3 trial) study. Starting in 2010, the scientists sought to study the effect of vitamin D and fish oil for cancer prevention and cardiovascular health over the course of at least five years.

The study included 25,871 adults with no serious health problems at the get-go. The participants randomly got given vitamin D (at 2,000 international units a day), fish oil (at 1,000 milligrams a day), or both, or they were given an equivalent placebo. The participants did not know if they were in either the supplements or the placebo groups.

All of the participants agreed to limit how much vitamin D they took outside the trial to no more than 800 UIs a day (the high end of the recommended daily dose from the NIH) and they agreed to not start taking fish oil at all.

The initial results, published in 2018, are not a resounding endorsement of vitamin D or fish oil for cancer or cardiovascular health. But ultimately, the study and the data are a trove for researchers to come back to again and again — it is a placebo-controlled, long-lasting study and it includes thousands of people who come from relatively diverse backgrounds. Hence we get the most recent study: This group looked at the participants’ rate of autoimmune diseases.

Over the course of five years or more, people taking vitamin D appear 22 percent less likely to develop an autoimmune disease. After two years, the difference was already pronounced; people in the vitamin D group had 39 percent fewer diagnoses than people in the placebo group. This finding suggests taking the supplements over time may be key to the protective effect hinted at here.

Meanwhile, people taking fish oil appear 15 percent less likely to be diagnosed with an autoimmune disease — this is not statistically significant, the researchers wrote. But when they factored in people who had the symptoms of an autoimmune disease but no diagnosis, the rate rose to 18 percent, which is statistically significant.

“[T]hese are well tolerated, non-toxic supplements, and other effective treatments to reduce the incidence of autoimmune diseases are lacking”

People who take both vitamin D and fish oil may fare even better: In this group, participants had 30 percent fewer autoimmune disease diagnoses than the placebo.

Curiously, no matter what the autoimmune diagnosis, the results held, suggesting there may be a more fundamental immune mechanism at play.

How This Affects Longevity — There are many autoimmune diseases, all of which have varying degrees of severity and effect on one’s quality of life. As many as 23.5 million Americans have an autoimmune condition, and some people with autoimmune diseases have a shorter life expectancy than the general population.

Like all chronic health issues, autoimmune diseases can diminish a person’s quality of life. For example, inflammatory bowel disease, which can manifest as Crohn’s disease or ulcerative colitis, was the most common diagnosis among the VITAL study participants; it can cause diarrhea, fatigue, abdominal pain and cramping, blood in the stool, and unintended weight loss. Together, these symptoms can hamper an individual’s ability to participate in the day-to-day activities others take for granted, such as going to work, traveling, or even just going out to dinner.

Why It’s a Hack — Vitamin D supplements are abundant and non-toxic, so while the science as to their effect on immunity is still up for debate, taking them may do you no harm. A third of U.S. adults are vitamin D deficient and medical professionals mostly agree that supplements can help people get adequate vitamin D (and may even be better than sunlight because of skin cancer risk). Another way forward may be to incorporate more vitamin D rich foods in your diet — from fortified cereals and milk to oily fish like salmon or mackerel, you have options.

In the study, the authors write that their results suggest vitamin D represents a simple intervention that could reduce the burden of autoimmune diseases. From the paper:

Autoimmune diseases are a group of heterogeneous conditions with similar underlying pathogenetic mechanisms and together are associated with considerable morbidity and mortality. The clinical importance of these findings is high because these are well tolerated, non-toxic supplements, and other effective treatments to reduce the incidence of autoimmune diseases are lacking. Additionally, we saw consistent results across autoimmune diseases and increasing effects with time.

As to whether the same can be said of fish oil, the jury is still very much out. Similar to vitamin D, fish oil can also come from your diet. Ultimately, talk to your healthcare provider before you make major dietary changes or start taking supplements for the first time.

Hack Score — Four out of ten stinky pills after breakfast 💊💊💊💊