Vitamin D is widely recognized for its vital role in supporting bone health, muscle function, and the immune system—but health experts caution that supplements aren’t always necessary, and may not offer the sweeping benefits many assume.
“Vitamin D is essential for good health,” says Dr. JoAnn Manson, head of preventive medicine at Brigham and Women’s Hospital. “The question is: do we really need to take supplements?” For most people, the answer is no—unless they have a deficiency confirmed by a blood test.
According to the U.S. National Library of Medicine, roughly 35% of American adults are deficient in vitamin D, with higher risk among individuals who are obese, over 65, have darker skin, or live in care facilities. In nursing homes and hospitals, that rate climbs to between 50% and 60%.
Vitamin D is unusual among nutrients because the body can produce it naturally through sun exposure. Just 10 to 15 minutes of direct sunlight on bare skin per day is usually sufficient, says Dr. Clemens Bergwitz, an endocrinologist at Yale School of Medicine. However, experts like Dr. Kseniya Kobets of Montefiore Einstein warn against overexposure, noting the risk of skin cancer and premature aging from ultraviolet radiation.
Aside from sunlight, vitamin D is also found in fatty fish, beef liver, egg yolks, mushrooms, and fortified foods such as milk, cereal, and plant-based dairy alternatives.
The vitamin plays a crucial role in absorbing calcium and maintaining bone density, which helps prevent conditions like osteoporosis. It also supports immune function, reduces inflammation, and aids in nerve and muscle activity.
However, when it comes to vitamin D supplements, the science is more nuanced. Despite being marketed for a wide range of health benefits—from reducing cancer and heart disease risk to boosting brain function—clinical research has shown limited evidence for most of these claims.
A large 2023 study published in The Lancet Diabetes & Endocrinology found no significant reduction in bone fractures among more than 21,000 older adults taking vitamin D supplements over five years. A separate 2024 study echoed these findings.
Dr. Manson is leading a long-term study called VITAL, involving over 25,000 participants, to investigate the potential health impacts of vitamin D and omega-3 supplements. While the study has not confirmed a reduced risk of heart disease or cancer, it has shown some promise in lowering the risk of autoimmune diseases and advanced-stage cancers.
Experts agree that supplements are beneficial for those who are deficient, but unnecessary for most people. “Unless you’re low in vitamin D, taking extra likely won’t offer significant health improvements,” says Dr. Bergwitz.
