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Even though it's not actually a vitamin—it's technically a prohormone, a substance our bodies convert into hormones to aid in various tasks—vitamin D is a pretty apt name. That's because it's a pretty big Deal. Vitamin D helps our bodies absorb calcium to bolster bones, may reduce risk for developing certain mental illnesses and plays a part in lowering susceptibility to several chronic diseases, the National Institutes of Health confirms.

While our bodies can make it naturally after being exposed to the sun, about 10% of our daily requirements are not usually covered by catching rays (and it can be less if you live in a less-sunny climate). That's where vitamin D foods and drinks come in clutch.

We're always proponents of focusing on food first to cover your nutritional needs, but in some cases and during certain times of year (like if you live in an area that doesn't receive a lot of sunlight in winter or if you follow a vegan diet), your doctor might recommend supplementation to help fill in the gaps. (ICYMI, here are 5 sneaky signs you might have a vitamin D deficiency.)

On the heels of new research published in May 2022 in the International Journal of Epidemiology, there might be one more reason to really lean into a D-strong diet or to ask your doctor about supplementation. This is especially true if you think you might fall under the umbrella of the 4 in 10 Americans who are vitamin D-deficient.

After examining data from nearly 300,000 people, scientists found that there is a direct, causal connection between low levels of vitamin D and higher levels of chronic inflammation, an internal body response that plays a part in everything from heart disease and diabetes to Alzheimer's disease and some autoimmune diseases.

Vitamin D rich foods
Credit: Getty Images

What This Study Found

As a refresher, acute inflammation is part of the body's natural healing process. Think of that bump and bruise that arises after accidentally kicking your shin on your bed frame, or the sore throat you experience when it's infected by strep bacteria and trying to fight them off. Those types of inflammation are short-lived, natural and actually beneficial. But long-term inflammation, which you might not even be able to feel or see, can do a number on your body and overall health. Persistent, or chronic, inflammation can contribute to multiple serious ailments and many of the most common causes of death in America, including heart disease, type 2 diabetes and certain kinds of cancer, Harvard Medical School experts report.

Previous studies have suggested a connection between vitamin D and chronic inflammation, but they didn't yet prove a causal relationship. So the scientists involved in this research wanted to gather a large pool of people to see if they could pinpoint which was the chicken and which was the egg, so to speak.

Epidemiologists at the University of South Australia tapped into the UK Biobank to analyze data from 294 ,970 participants who had complete data for race, gender orientation, vitamin D levels and C-reactive protein levels (an indicator of inflammation). By looking into the findings from 2006 to 2009, they were able to chart the relationship between vitamin D and C-reactive protein. They realized that those who had lower serum vitamin D levels displayed higher levels of C-reactive protein, a marker of chronic inflammation. After vitamin D levels rose out of severe deficiency, chronic inflammation markers tended to tame down.

"The shape of the observed association supports the previously proposed 'threshold effect,' suggesting that correction of vitamin D deficiency in the affected individuals is likely to reduce systemic low-grade inflammation and potentially mitigate the risk or severity of chronic illnesses with inflammatory components," the researchers explain in the study.

High levels of C-reactive protein are generated by the liver in response to inflammation, Ang Zhou, Ph.D., lead researcher and research associate in the nutritional and genetic epidemiology group at the Australian Centre for Precision Health, adds to University of South Australia Media Centre.

"When your body is experiencing chronic inflammation, it also shows higher levels of C-reactive protein. This study examined vitamin D and C-reactive proteins and found a one-way relationship between low levels of vitamin D and high levels of C-reactive protein, expressed as inflammation," Zhou says. "Boosting vitamin D in people with deficiencies may reduce chronic inflammation, helping them avoid a number of related diseases."

The Bottom Line

While more research is needed on a more diverse population pool and perhaps involving an intervention (say, prescribing a vitamin-D rich diet to those who are deficient who have high levels of inflammation), this study offers a promising clue that we may have another tool in our toolbox to help trim risk for chronic illnesses with an inflammatory element: vitamin D.

"We have repeatedly seen evidence for health benefits for increasing vitamin D concentrations in individuals with very low levels, while for others, there appears to be little to no benefit. These findings highlight the importance of avoiding clinical vitamin D deficiency, and provide further evidence for the wide-ranging effects of hormonal vitamin D," Elina Hyppönen, Ph.D., senior investigator, professor of epidemiology and director of University of South Australia's Australian Centre for Precision Health, adds in the research recap.

If you think you might be shy on vitamin D, your doctor can run a blood test. And if you'd like to get a head start on some delicious dinners loaded with vitamin D, add our Superfood Chopped Salad with Salmon & Creamy Garlic Dressing, Eggs in Tomato Sauce with Chickpeas & Spinach and Polenta Bowls with Roasted Vegetables & Fried Eggs to your menu this week.