You probably aren't getting enough vitamin D—here's what the experts say
It’s the most popular supplement on the market. But why do we need vitamin D—and why is the advice on how to get it so contradictory?
Vitamin D is a key nutrient for health. Not only does it help keep your bones strong, but it also assists with muscle and immune function. Yet, vitamin D stands at the center of a hotly debated wellness paradox.
Researchers agree that we generally aren’t getting enough vitamin D, but they can’t see eye to eye on how much is actually “enough,” what levels constitute a deficiency, or what benefits—if any—supplements provide, particularly for young and otherwise healthy people.
Advice on how to get vitamin D is also conflicting. Sunlight is the best source, but we’re told to cover up to avoid skin cancer. Then we’re advised to eat a diet rich in vitamin D even though most foods don’t contain enough of it.
Now, research published in April 2025 in the journal Nutrients is adding to the confusion. The review of existing scientific literature suggested that “optimal” vitamin D levels are “crucial” in preventing colorectal cancer and improving the course of the disease thanks to its anti-inflammatory and antioxidant properties. This finding led to headlines declaring that vitamin D lowers risk of colon cancer.
(Colon cancer is rising among young adults. Here are signs to watch for.)
However, the new study does not actually prove that vitamin D can prevent or treat colorectal cancer. In fact, only a handful of the randomized controlled trials included in the study—the gold standard in scientific research—even included people with the disease. Many of those that did were clinically insignificant.
This review, and many others like it, instead prove that our understanding of vitamin D and its impact on the prevention and treatment of certain diseases is still in its infancy.
“Vitamin D has important roles, but they’re probably not as broad as people say they are,” says Anne Cappola, an endocrinologist and professor of medicine at Penn Medicine. “That's part of the confusion behind wondering what you should be doing or taking, and how important that is.”
Here’s what to know about vitamin D, what it actually does for your health, and how to navigate confusing advice.
What vitamin D does—and does not do—for your health
Vitamin D helps your body absorb calcium from food, which keeps your bones strong and helps prevent osteoporosis, a disease that causes bones to become thinner and less dense. Vitamin D also protects you from more severe conditions such as osteomalacia, or “bone softening,” and it shields kids from rickets, a disease that causes weak bones, bowed legs, and other bone deformities that disproportionately affect Black children.
Vitamin D also plays important roles in muscle movement, communication between nerves, and immune defenses against bacteria and viruses, according to the National Institutes of Health’s Office of Dietary Supplements.
Dozens of studies have found that treating people with vitamin D is associated with reduced risks of some cancers, type 2 diabetes, cognitive disorders, and cardiovascular disease, among other chronic, autoimmune, and infectious diseases.
(Reversing type 2 diabetes is possible. Here's how.)
However, large reviews of these studies show that most of those benefits are inconclusive or insignificant. One meta-analysis published in April 2025 in the Lancet, for example, concluded that vitamin D supplements do not protect against respiratory infections.
The U.S. Preventive Services Task Force in both 2014 and 2021 recommended against screening the general population for vitamin D deficiency, citing insufficient evidence to support the practice. And according to a draft recommendation statement released in December 2024, the USPSTF is on track to recommend against vitamin D supplementation to prevent falls or fractures in postmenopausal women and men ages 60 and older.
“There are so many recommendations out there, so how do we prioritize what we should be doing and which are the most important things to do?” Cappola says. “In some ways it would be easy if all we had to do was take supplements, but it’s more complicated than that.”
Who’s at risk of a vitamin D deficiency—and what are the symptoms?
What’s much better understood is the fact that people across the globe aren’t getting enough vitamin D, making it the most popular supplement on the market.
All our bodies really need to make the nutrient is sunlight, yet estimates show that about 25 percent of Americans and about 40 percent of Europeans are deficient in vitamin D, a problem that’s also highly prevalent in the sunny Middle East, Asia, and Australia.
(5 things you should know before taking that supplement.)
That said, anyone can be deficient in vitamin D, and certain factors can raise your risk.
The older you become, the harder it is for your thinning skin to produce vitamin D when exposed to sunlight, with production decreasing by about 13 percent each decade.
People with darker skin have more of the melanin pigment that absorbs the UV rays essential to vitamin D production (more on this in a bit), so naturally they make less of it, says Henry Lim, a dermatologist with Henry Ford Health. Some estimates show that darker skin is about 90 percent less efficient at making vitamin D compared to lighter skin.
Because vitamin D is stored in fat, certain conditions that limit fat absorption, such as Crohn's disease, ulcerative colitis, and celiac disease, as well as weight loss procedures like gastric bypass surgery, can lead to deficiency.
Similarly, people with obesity need two to three times more vitamin D because their bodies store more of the nutrient in fat cells, leading to lower amounts circulating in the blood, Cappola says. As rates of obesity increase worldwide, we could see vitamin D deficiencies continue to rise as well, she adds.
Others at risk of vitamin D deficiency are pregnant people, breastfed infants, people living in northern latitudes that get less sun, and those taking certain medications to treat conditions like AIDS and seizures. The body turns vitamin D into its active form via a two-step process that starts in the liver and ends in the kidney, so anyone with advanced diseases in either organ face greater risks of deficiency as well.
A vitamin D deficiency, diagnosed with a blood test, often doesn’t cause symptoms, but some people with a severe case may experience fatigue, bone pain, and muscle weakness.
How do you get vitamin D from the sun?
Two kinds of ultraviolet rays reach the Earth’s surface and penetrate our skin: UVA is mostly responsible for tanning and aging the skin, while UVB is associated with sunburns and vitamin D production. Both can cause skin cancer.
For people with lighter skin, 10 to 20 minutes of sun exposure three times a week is considered enough to provide adequate vitamin D levels, Lim says. Darker-skinned people require about three to five times longer exposure to make the same amount.
But these general recommendations are highly dependent on the season, time of day, and latitude, Lim says.
Vitamin D production primarily occurs between 10 a.m. and 3 p.m., when the sun is most overhead, research has found. During the early morning, late afternoon, and wintertime, the angle of the sun increases in a way that UVB rays are forced to travel a longer distance through the ozone layer, which absorbs them in the process.
(How much SPF is enough? Here's what to know about sunscreen.)
Clouds, windows, and air pollutants such as ozone and nitrogen dioxide also soak up UVB rays, reducing the amount that hits your skin and thus decreasing vitamin D production, Lim says.
Sunscreen has long been thought to disrupt this process as well, but newer studies have found that’s not the case in most people.
Still, depending on the sun for vitamin D is unpredictable and inconsistent at best, and many people aren’t getting enough of it as increasing skin cancer awareness sends people indoors, Lim says.
In fact, the American Academy of Dermatology says adults should not get vitamin D from sun exposure or indoor tanning, but rather from foods “naturally rich” in or fortified with vitamin D—which is problematic because not many exist.
What foods are high in vitamin D—and why is it so hard to get enough?
Foods are notoriously poor in vitamin D, says Monique Richard, a registered dietician nutritionist and owner of Nutrition-In-Sight.
The best natural sources of vitamin D are fatty fish like trout, tuna, salmon, and mackerel, as well as fish liver oils and mushrooms that have been exposed to UV light. Smaller amounts are found in egg yolks, cheese, and beef liver.
Because most people don’t eat enough of these foods every day, certain products like milk, cereals, orange juice, and yogurt, as well as plant-based alternatives like soy, almond, and oat milks, are fortified with vitamin D in the United States and other countries such as the United Kingdom and Finland.
But it’s still not enough. Milk, for example, is fortified with about 120 IU of vitamin D per cup, or 3 micrograms. People under 70 would have to drink about five cups of milk every day—or at least ensure they eat other foods like cereal and salmon—to meet the minimum recommended daily intake of 600 IU (15 mcg), according to the Endocrine Society. (Adults older than 70 should consume at least 800 IU, or 20 mcg, of vitamin D a day.)
So… how do I get enough vitamin D?
That said, vitamin D is more accessible than you might think.
It’s about finding a balance between sensible sun exposure, a diet rich in vitamin D, and supplementation that works for you. (Sensible sun exposure involves seeking shade, wearing protective clothing, and applying sunscreen with an SPF of 30 or higher.)
If you choose to take vitamin D supplements, which come in many forms like pills and droplets, make sure you don’t overdo it.
Too much vitamin D can cause nausea, muscle weakness, confusion, vomiting, and dehydration; in severe cases, it can cause kidney stones and kidney failure, irregular heartbeat, and death, the NIH says.
Vitamin D intoxication isn’t possible with sun exposure because your skin limits how much vitamin D it makes.
It doesn’t hurt to be more mindful about vitamin D, Cappola says, but if you don’t have an existing deficiency, going out of your way to seek more of it won’t do much, research has found.
“You definitely want to have enough,” Cappola says, “but more is not always better.”
