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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 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, 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, Dr. 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 Dr. 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, Dr. 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.
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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.
That said, in the right amount, vitamin D is strongly connected to a variety of positive aspects of health, the most well-supported or notable of which we point out here. So with those caveats in mind, here are some key health benefits of getting enough vitamin D:
1. Vitamin D can help build strong bones.
Vitamin D is crucial for a strong, healthy skeleton in several ways. Vitamin D helps your body absorb calcium, the main building block of bones. It also helps your bone cells grow and rebuild, and promotes bone health by helping the surrounding muscles grow properly, the ODS says.
If your body doesn’t get enough vitamin D to help it absorb calcium from the food you eat, it may start siphoning off calcium stored in your skeleton, according to the National Institute of Arthritis and Musculoskeletal and Skin Diseases, which can cause bone weakening and prevent the growth of strong bones. That’s why not getting enough vitamin D can contribute to osteoporosis, the ODS says. A vitamin D deficiency can also lead to osteomalacia, or weakening of the bones, per the ODS.
2. Vitamin D can support a healthy immune system.
Vitamin D plays several important roles in regulating immune health, and we know that vitamin D supports important cells in the immune system, Shana Minei Spence, M.S., R.D.N., C.D.N., a registered dietitian nutritionist based in New York City, tells SELF. While scientists don’t yet know all the exact mechanisms, one line of thinking is that vitamin D may increase the production of a substance called cathelicidin, an immune system protein that fights invading pathogens like viruses and bacteria. Vitamin D is also thought to play a role in regulating the production of substances and cells that cause inflammation in the immune system.
The thinking that vitamin D may help your immune system fight off infections is obviously a hot topic during the COVID-19 pandemic. While the NIH’s COVID-19 Treatment Guidelines cites vitamin D’s potential to impact the immune system, they also say there isn’t yet enough data either way to say if it works as a prevention or treatment for COVID-19.
That said, experts have been talking about vitamin D as a cold and flu fighter for a while. A research review published in Inflammation & Allergy—Drug Targets in 2013 cites several large studies showing that adequate vitamin D levels are associated with a lower risk and severity of respiratory infections, while vitamin D deficiencies are associated with a greater risk and severity. And some research on vitamin D supplements suggests, they could help ward off these kinds of illnesses. A review of 25 studies published in the British Medical Journal in 2017 suggested that vitamin D supplementation reduced the risk of acute respiratory tract infections in people with vitamin D levels in the deficiency range or on the lower end of the normal range by 12% overall. The more deficient people were, the more beneficial the supplements were. (Fun fact: Sun lamps and cod liver oil, both sources of vitamin D, were even used to fight tuberculosis in the 19th and early 20th centuries.)
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What’s more, “Vitamin D deficiency has been shown to be prevalent in autoimmune disease,” Spence says. According to a research review published in Nutrients in 2020, there is an association between low vitamin D and autoimmune diseases such as psoriasis, multiple sclerosis, and rheumatoid arthritis. (That said, taking more vitamin D hasn’t been shown to prevent these diseases.)
3. Vitamin D can promote healthy blood sugar levels.
Vitamin D plays a key role in metabolizing glucose in the food you eat. It stimulates the beta cells in your pancreas to secrete insulin, a hormone that is key for converting food you eat into energy and regulating blood sugar, Dr. Shapses explains. It also reduces insulin resistance (when your body stops responding as well to insulin), according to the ODS, and could play a role in preventing the onset of type 2 diabetes.
While a number of observational studies show an association between low vitamin D and higher blood sugar levels (in people with and without diabetes) as well as an increased risk of diabetes, so far there is “little evidence” of a cause-and-effect relationship between taking extra vitamin D supplements and diabetes risk or blood sugar control, the ODS explains—especially in people who already get enough vitamin D.
4. Vitamin D can help support a healthy pregnancy.
Consider this another reason to take a prenatal vitamin. As SELF has reported, it’s important for pregnant people to get enough vitamin D in their diets. A 2019 Cochrane review suggests that vitamin D supplementation in pregnant people might reduce the risk of pregnancy complications like pre‐eclampsia, gestational diabetes, low birth weight, and severe postpartum hemorrhage. Although the mechanisms behind this are not fully understood, some of these benefits might come from vitamin D’s positive effects on the immune system, inflammation, and blood vessel function.
5. Vitamin D can potentially reduce your risk of getting or dying from cancer.
Lab experiments and animal studies indicate that vitamin D could inhibit cancer formation and tumor growth, according to the ODS, while the research in humans is mixed—but exciting.
There are some observational studies and clinical trials suggesting low vitamin D levels are connected to developing or dying from multiple types of cancer—including breast, prostate, and colorectal cancer—as well as many that do not.
The ODS cites two large meta-analyses of studies finding that higher vitamin D levels were associated with a reduced overall incidence of cancer and death from cancer (but not in every study or demographic). There is some promising clinical data too. A 2019 meta-analysis published in the Annals of Oncology looked at 10 randomized clinical trials including 6,537 cancer cases and found that vitamin D supplementation reduced cancer mortality rates by 13%. Ultimately, however, experts say that more research is needed before they can say anything such as “vitamin D can help prevent cancer.”
How to get enough vitamin D
So, how much vitamin D do you need to ensure it’s helping to promote good health? The benefits of vitamin D come from consuming a sufficient amount—not too little, not too much.
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To get the benefits of vitamin D, you need to avoid deficiency, says Dr. Shapses. Vitamin D deficiency occurs when you have a blood level of 20 nanograms per milliliter (ng/ml) or less, according to the ODS. Severe deficiency is 12 ng/ml or less. “It’s when levels go below 20, but especially below 12, that we see negative outcomes associated with low vitamin D status,” Dr. Shapses says. But you don’t want to veer too far in the other direction, either, because it is possible to take in too much vitamin D through supplements, according to the ODS, causing symptoms such as confusion, nausea, and vomiting (or even kidney failure at extremely high levels).
Sunlight is one great source for keeping your vitamin D at healthy levels. Research suggests that just five to 30 minutes of sun exposure per day, or at least twice weekly, is generally enough to make the vitamin D you need, according to the ODS. (And you should still wear sunscreen any time you’re outside—most people don’t put on enough to block the vitamin D–producing rays from reaching your skin anyway, the ODS says.) While people with darker skin produce less vitamin D with the same amount of sun exposure than people with lighter skin because of the presence of melanin, the ODS says it’s not clear if the lower levels of vitamin D more common in Black people because of this reason have negative health effects; there aren’t official recommendations for people with darker skin to spend more time in the sun.
Although vitamin D is the sunshine vitamin, don’t solely rely on the sun to meet your needs, says Spence—you’ll also want to get it from a variety of foods. The Recommended Daily Allowance (RDA) for vitamin D is 600 International Units (IU) of vitamin D per day for women ages 19 to 70, according to the ODS. Mushrooms, fatty fish, and egg yolks are great nutritional sources, Spence says. While processed and packaged foods are sometimes painted as less healthy, Spence says, they can actually be an extremely important source of vitamin D. “Many foods such as cereals, milks (both cow and plant-based), yogurt, and juices are fortified with vitamin D,” she says.
While many people are able to get enough vitamin D from the food and sun, some do not. Estimates on how common vitamin D deficiency is vary, but National Health and Nutrition Examination Survey data from 2011 to 2014 show that 18% of people over the age of 1 in the U.S. were at risk of inadequate levels, and 5% were at risk of deficiency.
So if you don’t eat vitamin D–rich foods on the regular or are deficient in vitamin D for any reason really, you might also benefit from a vitamin D supplement. “Many clients that I work with have trouble eating a variety of foods,” says Spence. “I often recommend clients just take a supplement for support,” whether that’s a stand-alone vitamin D supplement or a multivitamin.
As with any kind of dietary supplement, taking vitamin D is something to discuss with a health care provider like your primary care doctor first. If you’re wondering whether you’re getting enough vitamin D to reap the benefits, schedule an appointment. Your provider might recommend a simple blood test to check your vitamin D levels. If your levels are low, they will probably suggest or prescribe a supplement with the right level of vitamin D to bring your levels into the target zone—and make sure you’re not missing out on any of that vitamin D goodness.
