You’ve probably heard by now that vitamin D is good for you, and maybe you’ve even thought about taking a supplement in hopes of maximizing your vitamin D benefits. (After all, vitamin D is one of the most Googled dietary supplements, according to research in the journal Nutrients.)
Vitamin D has long been best known for its ability to strengthen bones and more recently has also been linked to several additional health benefits, especially in the COVID-19 era. But sometimes these rumors about vitamin D benefits are inaccurate. When it comes to vitamins and your health, it can be hard to know what’s for real.
To get to the bottom of what vitamin D can actually do for your body, we asked experts to cut through the hype and explain what we know about vitamin D benefits.
What is vitamin D?
First, a quick explanation about what this stuff is, exactly. Vitamin D is no average nutrient, and its name is actually something of a misnomer. “It’s not just a vitamin,” Sue Shapses, Ph.D., R.D., a professor of nutritional sciences at Rutgers University, tells SELF. “It’s a hormone, so it acts on many organs throughout the body.” Although we can get it through food, our bodies actually produce their own vitamin D (with the help of sunlight) and have their own receptors for vitamin D, which has a molecular structure similar to other hormones—all of which makes it more like a hormone than a true vitamin. To avoid confusion for the purposes of this article, we’ll continue to refer to it as a vitamin throughout—but it’s an interesting fact, right?
Vitamin D gets into your system in two ways: You ingest it, or you make it. Vitamin D is a fat-soluble nutrient found in some foods, such as milk and salmon, and dietary supplements, according to the Office of Dietary Supplements (ODS) at the National Institutes of Health (NIH). Our bodies also make vitamin D from sunlight, which is why it’s sometimes called the sunshine vitamin. Within minutes of going outside, your skin begins to convert UV light from the sun into previtamin D3, says Dr. Shapses. Then it travels through your blood, liver, and kidneys, where it’s converted to the active form of vitamin D, Shapses explains. This D3 is the kind of vitamin D your body can use, just like the version you eat.
From there, vitamin D is dispatched throughout the body so it can get to work. “In the active form, it can go to the vitamin D receptors on various areas of the body, various organs, including the pancreas, the brain, muscles, cardiac tissue—you name it,” says Shapses. Yes, your body has special vitamin D receptors. They enable vitamin D to do a myriad of things throughout your body, like reducing inflammation and affecting cell growth.
The benefits of vitamin D
Now, let’s get into what vitamin D can do for your body. While there’s a lot of buzz about the potential benefits of vitamin D—especially during the pandemic, as we’ll get to—the fact remains that vitamin D’s reputation as a bone builder is its most well-studied and evidence-backed benefit, Shapses says. Various other potential benefits are promising but not as proven, based on strong cell and animal studies and some encouraging studies of humans, Shapses says.
There are studies linking low vitamin D to an increased risk of many conditions, from heart disease to obesity to depression. But like with many nutrients, it can be really hard to tease out a causal relationship here—meaning we can observe a link between adequate intake of a specific nutrient, like vitamin D, and better health outcomes, but haven’t established whether it’s that particular nutrient that’s responsible for those benefits. And often, when researchers have given people vitamin D supplements to see if the intervention has the expected effect, the results come up short.