Vitamin D Benefits: Seasonal Affective Disorder, Bone Health, and More

8 Potential Vitamin D Benefits

8 Potential Vitamin D Benefits
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Updated on October 13, 2025
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Note: The U.S. Food and Drug Administration (FDA) does not approve supplements for safety or effectiveness. Talk to a healthcare professional about whether a supplement is the right fit for your individual health, and about any potential drug interactions or safety concerns.

It’s no secret that vitamin D is an essential nutrient, best known for its role in bone health and immune function. It’s often referred to as the “sunshine vitamin” because our bodies can make it when exposed to ultraviolet light, and most people get at least some of their daily requirement for the vitamin this way.

Only select foods, including eggs and fatty fish like salmon, naturally contain vitamin D. Many other foods, including milk and orange juice, have been fortified with the nutrient. Why such an emphasis on this fat-soluble vitamin?

Research has linked vitamin D to a number of health benefits, noting that it may improve or prevent issues ranging from seasonal depression to heart disease and cancer.

8 Possible Health Benefits of Vitamin D You Should Know About

Although research on vitamin D abounds, its effect on human health remains uncertain. That’s largely because the majority of vitamin D studies are either on animals or were conducted in small groups of people. Most importantly, the majority of research on the nutrient is observational, meaning that the findings don’t point to a definite cause-and-effect relationship between vitamin D and the potential health benefit being studied.

Studies that do produce likely causal results are conducted with a randomized, controlled model, in which researchers eliminate the risk of bias and account for potentially conflicting factors.

 Large randomized, controlled trials are considered the gold standard for research, and unfortunately, there haven’t been many on vitamin D supplementation and its various possible health benefits.

With research limitations in mind, here’s an in-depth look at what vitamin D may do for your health.

1. It Can Help Prevent Bone Diseases, Such as Osteoporosis

It’s clear that vitamin D aids in the absorption of calcium. Without enough vitamin D in the body, there will not be enough of calcium’s active form, the hormone calcitriol.

 Calcium absorption allows the body to maintain a sufficient level of that element as well as phosphate, both of which promote the growth and maintenance of healthy, strong bones.
That’s why getting enough vitamin D is critical for warding off bone diseases, such as rickets in children, osteomalacia in adults, and osteoporosis in older adults, according to the National Institutes of Health (NIH).

 Rickets is marked by soft and weak bones in children. It is rare in the United States and is typically associated with developing countries. However, research shows that an inadequate level of vitamin D from a lack of sun exposure or diet can affect children anywhere in the world.

 Signs and symptoms of rickets include pain in the spine, pelvis, and legs, as well as delayed growth and muscle weakness.

Osteomalacia refers to the softening of the bones due to vitamin D deficiency. Its signs include dull, aching pain in the legs, hips, pelvis, ribs, and back, though the condition often doesn’t have symptoms in its early stages.

Osteoporosis is one of the main causes of fractures and broken bones in older adults. This bone disease results when the cycle of new bone creation and old bone loss becomes unbalanced and more bone is lost than created.

 Women who are past menopause are at the highest risk of osteoporosis, and as with osteomalacia, people with osteoporosis are often asymptomatic when the disease is in its early stages. Later symptoms may include a stooped posture, declining height, back pain, and an unexpected and immediate bone fracture.
Given these facts, it’s no wonder that vitamin D supplements have long been touted as good for bone health. That said, observational research supports the idea that vitamin D supplements only make a meaningful difference if you have a deficiency. One study aimed to see if 2,000 international units (IU) of daily vitamin D3 supplements versus a placebo would reduce the risk of bone fractures over five years in over 25,000 healthy, nondeficient volunteers over age 50. And research confirmed that the supplements did not reduce risk.

However, this study relied on observational data with many confounding variables, so it can’t be used to make blanket assumptions, says Alana Serota, MD, an internal medicine and metabolic bone physician at the Hospital for Special Surgery in New York City.

An additional review of 18 randomized controlled trials found that vitamin D supplements don’t prevent fractures in older people. Still, since the study didn’t target people with a deficiency, it doesn’t negate the value of supplementation in patients who truly need it, Dr. Serota notes.

In fact, Serota says that vitamin D supplementation can help you achieve and maintain healthy vitamin D levels, particularly if you have or are at higher risk for a deficiency (like if you live in an area with long, dark winters).

2. It May Improve Symptoms of Seasonal Affective Disorder (Seasonal Depression)

While vitamin D’s potential role in helping prevent or manage clinical depression is still unclear because of limited research, researchers believe that a person’s vitamin D level may indeed play a role in the risk of seasonal affective disorder (SAD), or seasonal depression.

 Because there is less sunlight in winter, people tend to produce less vitamin D, which may affect the activity of the neurotransmitter serotonin and play a role in seasonal affective disorder.
Serotonin is the same chemical that your brain pumps out when you go on a long run, eat a piece of chocolate, or hold the hand of the person you love. It’s a feel-good hormone. So when the serotonin level is thrown off, you may feel blue or be at a greater risk for mood disorders.

However, the evidence is not strong enough to suggest vitamin D supplements can prevent or treat seasonal depression, says Serota. “We may be looking at an ice cream–shark attacks scenario: Shark attacks and ice cream intake increase in summer, but shark attacks are not caused by ice cream,” she says. In the same way, natural sunlight boosts vitamin D, while less sunlight lowers it. Both change with the seasons, but that doesn’t prove vitamin D deficiency directly causes SAD — it may just shift in parallel with light exposure.

Studies on the effectiveness of vitamin D as a depression treatment have had mixed results. In one recent review and meta-analysis, the researchers found that daily vitamin D supplementation equal to or exceeding 2,000 IU per day may help reduce depressive symptoms. However, the researchers described their results as having very low certainty and said more research is warranted to draw accurate conclusions.

“Systemic reviews and meta-analyses are only as good as the studies they include,” says Serota. In this particular instance, Serota says the studies included were mixed and generally of poor quality, which makes it difficult to draw definitive conclusions.

3. It May Protect Against Respiratory Infections

Increase your level of vitamin D if you’re deficient, and you may find that you get fewer respiratory infections (colds and flu) than usual. There’s even research to indicate that a vitamin D deficiency may worsen outcomes of COVID-19. A systematic review and meta-analysis of randomized, controlled trials found that supplementing with vitamin D may protect against negative outcomes related to COVID-19, although additional research is needed.

One review of 43 randomized, controlled trials involving about 49,300 people suggests that participants who took a daily dose between 400 and 1200 IU of vitamin D didn’t get as many respiratory infections. However, the review’s authors say taking extra vitamin D only slightly prevented infections and note that more clinical trials are needed.

Serota agrees, specifying that this is an interesting meta-analysis that warrants more context (like the starting vitamin D levels of all participants) to establish a true correlation.

4. It May Help Protect Against Heart Disease and Stroke

Is vitamin D heart healthy? One review linked vitamin D deficiency to a higher risk of heart disease, stroke, and heart failure, although it did not establish whether vitamin D levels alone were responsible for that effect.

Yet another study found that taking a much higher dose of vitamin D than recommended for five years did not affect total mortality or the incidence of cardiovascular disease in older men and women, most of whom had adequate intakes of the vitamin at the study’s onset.

To corroborate those findings, a review and statement released by the U.S. Preventive Services Task Force noted that vitamin D supplements have not been shown to prevent cardiovascular disease-related deaths, the outcome of a cardiovascular event, or stroke.

Additionally, recent research also showed that higher doses of vitamin D did not improve two key markers of cardiovascular disease (high-sensitivity cardiac troponin or N-terminal pro-B-type natriuretic peptide), suggesting supplementation may not provide the protective effects once hoped for.

Even though some evidence shows an association between low vitamin D levels and increased risk of these heart conditions, it doesn’t prove that a vitamin D deficiency is the cause, because the same factors that cause heart disease might also cause low vitamin D levels, says Jacob Teitelbaum, MD, a board-certified internist and integrative physician based in Kona, Hawaii, who is coauthor of Real Cause, Real Cure. He adds. “Because of this, I do not give vitamin D supplementation specifically to decrease heart attack and stroke risk.”

5. It Could Reduce the Risk for Type 2 Diabetes

A systematic review and meta-analysis of the current research suggests that vitamin D may help increase insulin sensitivity, boost beta cell function, and lessen inflammation — all potential benefits for reducing the risk of and helping to manage diabetes.

“Adding simple vitamin D supplements to the normal treatment plan may help kids with type 1 diabetes by protecting their beta cells, thereby prolonging the honeymoon period [the phase after diagnosis where the pancreas can still produce some insulin],” says Susan Trachman, MD, a board-certified psychiatrist who specializes in working with people who have medically unexplained illnesses and associate professor at George Washington University in Washington, DC. “The longer kids can produce insulin on their own, the better off they’ll be.”

Another meta-analysis found that supplementing adults with vitamin D reduced the risk of progressing from prediabetes to type 2 diabetes by about 15 percent.

 The study subjects had a high risk of developing type 2 diabetes but were not necessarily deficient in vitamin D.
In a different study with about 1,250 participants in Japan, vitamin D supplements weren’t found to reduce the risk of type 2 diabetes in people with prediabetes. However, results suggested that they could benefit people with insufficient insulin secretion.

Dr. Trachman notes that while both of these studies are published in respected journals, the findings conflict. In other words, the evidence is mixed, so it isn’t clear what role vitamin D supplements may play for those with prediabetes or diabetes.

6. It Might Play a Role in Reducing Cancer Death

Scientists are paying increasing attention to vitamin D’s possible role in warding off cancer. One systematic review found highly suggestive evidence that vitamin D3 supplementation could help reduce the incidence of some cancers (including head and neck, breast, colorectal, lung, and renal cell cancers).

 Another recent study also suggested that vitamin D supplements may help protect against breast cancer in women, including for Black and Latina women.

 Trachman notes that these results need to be studied in larger populations to establish a stronger link.
Because of conflicting science and a dearth of randomized, controlled trials, the NIH doesn’t yet recommend vitamin D supplements to help reduce the risk of cancer, though it does suggest that getting enough vitamin D may reduce the likelihood of dying from cancer.

Trachman agrees: “Evidence regarding the link between vitamin D and cancer mortality is mixed and still under active research,” she says. “Some studies suggest a potential benefit from vitamin D supplementation, but large clinical trials to date have produced inconsistent results.”

7. It May Help Prevent Cognitive Decline and Dementia

Robin Foroutan, RDN, an integrative dietitian at the Morrison Center in New York City, points out that there are vitamin D receptors in brain tissue, which suggests that the vitamin may play a role in cognitive function and, potentially, the risk of dementia. Research increasingly supports this notion — a study of about 5,300 cases linked vitamin D deficiency with an increased risk of dementia and justified its causal effect on the condition.

 Dr. Teitelbaum notes that while this isn’t a gold-standard, large-scale trial directly examining the effect in a study population, it effectively supports a causal link using the data available.
Other research emphasizes the importance for older people to address vitamin D deficiencies to improve health overall, though the study didn’t find a relationship specifically between vitamin D levels and cognitive function.

Meanwhile, a large review concluded that evidence is still inconsistent and insufficient to prove that vitamin D supplementation prevents or treats cognitive decline in neurodegenerative diseases like Parkinson’s. The authors point out that while lower vitamin D levels are often observed in people with these conditions, it’s unclear whether low vitamin D contributes to disease development or is simply a consequence of reduced mobility, less sun exposure, or other factors.

“Given the low cost and safety of reasonable vitamin D supplementation, I believe the evidence is strong enough to recommend a multivitamin containing 1000 units of vitamin D to prevent dementia and cognitive decline,” says Teitelbaum.

8. It Provides Relief for Symptoms of Autoimmune Conditions

Researchers have long been fascinated with the potential effect that vitamin D may have on autoimmune disorders because of the nutrient’s role in regulating the immune system.

Why? “Vitamin D deficiency is associated with an increased risk of autoimmune disorders, likely due to its anti-inflammatory properties,” says Trachman.

To confirm its role, more research is needed, but a study of more than 25,800 adults made some significant headway. The study found that people who took vitamin D, or vitamin D and omega-3 fatty acids, had a significantly lower rate of autoimmune diseases — like rheumatoid arthritis, polymyalgia rheumatica, autoimmune thyroid disease, and psoriasis — than people who took a placebo.

 However, this study has its limitations because it only observed the effects of vitamin D in older adults, even though many autoimmune disorders are diagnosed in a younger population, says Trachman.

How to Incorporate Vitamin D Into Your Lifestyle

The recommended daily allowance of vitamin D is 600 international units (IU) for most people ages 1 to 70. For people over age 70, it’s 800 IU, and for infants, it’s 400 IU.

But it’s not easy to get that much vitamin D through diet and sunlight alone. The average amount of the nutrient that an individual gets from food and drink rarely exceeds 204 IU per day in men and 168 IU per day in women. Even drinking whole milk fortified with vitamin D will get you only 95.6 IU in 8 ounces (oz).

 Unsweetened oat milk boasts 68 IU per 100 grams (which is about 3.5 oz),

 and the same amount of almond milk contains 63.6 IU.

That’s why many people take vitamin D supplements. However, large studies like the VITAL trial (a randomized clinical trial involving more than 25,000 participants) suggest that supplements don’t provide added benefits for bone health in generally healthy adults without a vitamin D deficiency.

 If you suspect that you have a deficiency, consult your primary care provider, as treatment recommendations vary widely.
Keep in mind that there can be too much of a good thing with vitamin D, which is why the NIH set a vitamin D upper limit of up to 3,000 IU for infants and children up to age 8, depending on age, and 4,000 IU per day for people over age 9. Dosages beyond those increase the risk of death, cancer, and cardiovascular events, as well as falls and fractures in older adults.

The Takeaway

  • Vitamin D is an essential nutrient that can help fortify and strengthen bones while also potentially preventing respiratory infections and lowering the risk of death from certain types of cancer for some individuals.
  • Studies haven’t yet conclusively shown vitamin D’s potential benefits with regard to mood and seasonal depression, prediabetes and diabetes, and autoimmune disorders, and more research is needed.
  • Make sure to get your recommended daily amount of the nutrient through food, supplements, and sunlight (keeping in mind the health risks of prolonged UV ray exposure).
  • If you suspect that you have a vitamin D deficiency, talk to your doctor about getting a blood test to check if your level is adequate.

Additional reporting by Melinda Carstensen, Kayla Blanton, and Kathleen Ferraro.

EDITORIAL SOURCES
Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.
Resources
  1. Vitamin D. National Institutes of Health Office of Dietary Supplements. June 27, 2025.
  2. Study Design 101: Randomized Controlled Trial. George Washington University Himmelfarb Health Sciences Library. September 25, 2023.
  3. Lung BE et al. Calcitriol. StatPearls. March 27, 2025.
  4. Dumbre D et al. Unraveling the Relationship Between Vitamin D and Noncommunicable Diseases: A Systemic Review and Meta-Analysis. Public Health Nursing. May-June 2025.
  5. Rickets. Mayo Clinic. April 25, 2025.
  6. Osteomalacia. Cleveland Clinic. February 20, 2025.
  7. Osteoporosis. Mayo Clinic. February 24, 2024.
  8. LeBoff MS et al. Supplemental Vitamin D and Incident Fractures in Midlife and Older Adults. The New England Journal of Medicine. July 28, 2022.
  9. Khatri K et al. Role of Calcium &/or Vitamin D Supplementation in Preventing Osteoporotic Fracture in the Elderly: A Systematic Review & Meta-Analysis. The Indian Journal of Medical Research. January 2023.
  10. Seasonal Affective Disorder. National Institute of Mental Health. 2023.
  11. Bamalan OA et al. Physiology, Serotonin. StatPearls. July 30, 2023.
  12. Mikola T et al. The Effect of Vitamin D Supplementation on Depressive Symptoms in Adults: A Systematic Review and Meta‐analysis of Randomized Controlled Trials. Critical Reviews in Food Science and Nutrition. July 11, 2022.
  13. Varikasuvu SR et al. COVID-19 and Vitamin D (Co-VIVID Study): A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Expert Review of Anti-Infective Therapy. February 3, 2022.
  14. Wang CH et al. Optimal Methods of Vitamin D Supplementation to Prevent Acute Respiratory Infections: A Systematic Review, Dose-Response and Pairwise Meta-Analysis of Randomized Controlled Trials. Nutrition Journal. August 14, 2024.
  15. Haider F et al. Vitamin D and Cardiovascular Diseases: An Update. Cureus. November 30, 2023.
  16. Ebeling PR. Does Vitamin D Supplementation Reduce Cardiovascular Events and Cancer? The American Journal of Clinical Nutrition. May 2022.
  17. Vitamin, Mineral, and Multivitamin Supplementation to Prevent Cardiovascular Disease and Cancer. JAMA. June 21, 2022.
  18. Rainer KW et al. Effects of vitamin D supplementation on cardiac biomarkers: Results from the STURDY trial. American Journal of Preventive Cardiology. December 2024.
  19. Argano C et al. The Role of Vitamin D and Its Molecular Bases in Insulin Resistance, Diabetes, Metabolic Syndrome, and Cardiovascular Disease: State of the Art. International Journal of Molecular Sciences. October 23, 2023.
  20. Pittas AG et al. Vitamin D and Risk for Type 2 Diabetes in People With Prediabetes: A Systemic Review and Meta-analysis of Individual Participant Data From 3 Randomized Clinical Trials. Annals of Internal Medicine. March 2023.
  21. Kawahara T et al. Effect of Active Vitamin D Treatment on Development of Type 2 Diabetes: DPVD Randomised Controlled Trial in Japanese Population. The BMJ. May 25, 2022.
  22. Petrelli F et al. Vitamin D3 and cancer risk in healthy subjects: An umbrella review of systematic review and meta-analysis. Clinical Nutrition ESPEN. October 2024.
  23. O’Brien KM et al. Vitamin D Concentrations and Breast Cancer Incidence Among Black/African American and Non-Black Hispanic/Latina Women. Cancer. July 1, 2022.
  24. Navale SS et al. Vitamin D and Brain Health: An Observational and Mendelian Randomization Study. The American Journal of Clinical Nutrition. August 2022.
  25. Imerbsin N et al. Vitamin D and Cognitive Impairment. Nutrients. April 9, 2025.
  26. Fullard ME et al. A Review of the Relationship Between Vitamin D and Parkinson Disease Symptoms. Frontiers in Neurology. May 27, 2020.
  27. Vitamin D. Harvard T.H. Chan School of Public Health. March 2023.
  28. Hahn J et al. Vitamin D and Marine Omega 3 Fatty Acid Supplementation and Incident Autoimmune Disease: Vital Randomized Controlled Trial. The BMJ. January 26, 2022.
  29. Milk, Whole, 3.25% Milkfat, With Added Vitamin D. U.S. Department of Agriculture FoodData Central. December 16, 2019.
  30. Oat Milk, Unsweetened, Plain, Refrigerated. U.S. Department of Agriculture FoodData Central. April 28, 2022.
  31. Almond Milk, Unsweetened, Plain, Refrigerated. U.S. Department of Agriculture FoodData Central. April 28, 2022.
  32. LeBoff MS et al. Supplemental Vitamin D and Incident Fractures in Midlife and Older Adults. The New England Journal of Medicine. July 27, 2022.
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Lynn Grieger, RDN, CDCES

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Lynn Grieger is a registered dietitian-nutritionist, certified diabetes care and education specialist, certified personal trainer, and certified health and wellness coach. She completed requirements to become a registered dietitian at Valparaiso University in 1987 and completed a dietetic internship at Ingalls Memorial Hospital in Harvey, Illinois, in 1988. 

Lynn brings her expertise in nutrition, exercise, and behavior change to her work in helping people reach their individual health and fitness goals. In addition to writing for Everyday Health, she has also written for websites and publications like Food and Health Communications, Today's Dietitian, iVillage.com, and Rodale Press. She has a passion for healthy, nutrient-dense, great-tasting food and for being outdoors as much as possible — she can often be found running or hiking, and has completed a marathon in every state.

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