Vitamin D Supplements

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 meet at least part of their daily requirement for the vitamin this way, according to the National Institutes of Health (NIH).

Only select foods, including eggs and fatty fish like salmon, naturally contain vitamin D, but many others, including milk and orange juice, have been fortified with the nutrient. Why such an emphasis on this fat-soluble vitamin? Well, research has linked vitamin D to a number of health benefits. Read on to learn what is known about what this essential nutrient can — and can’t — do for you.

How Is Vitamin D Different From Other Nutrients?

To get a better understanding of vitamin D and scientists’ long-held fascination with its functions, it’s first good to know that not all vitamins and minerals operate in the body alike.

“We’re discovering that vitamin D behaves much less like a vitamin and much more like a hormone,” says Robin Foroutan, RDN, an integrative dietitian at the Morrison Center in New York City and a spokesperson for the Academy of Nutrition and Dietetics. That means vitamin D acts as a messenger rather than a participant in metabolism, according to the Food and Nutrition Board (FNB) at the Institute of Medicine of the National Academies, potentially affecting everything from weight to how organs function.

How Do You Ensure That You Have Enough Vitamin D?

The recommended daily allowance of vitamin D is 600 international units (IU) for most people ages 1 to 70, per the FNB. 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), according to the U.S. Department of Agriculture (USDA). Unsweetened oat milk boasts 68 IU per 100 grams (which is about 3.5 oz) per the USDA, and the same amount of almond milk contains 63.6 IU, the USDA reports.

That’s why many people take vitamin D supplements. However, a study published in July 2022 in the The New England Journal of Medicine suggests that they may not be necessary or effective in those who don’t have 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 FNB set an upper limit of 4,000 IU per day in supplementation for people over age 9 and up to 3,000 IU for infants and children up to age 8, depending on age. Dosages beyond those increase the risk of death, cancer, and cardiovascular events, as well as falls and fractures in older adults, says the NIH.

What Research Says About Vitamin D and Health

Although research on vitamin D abounds, its effect on human health remains uncertain. That’s largely because the majority of vitamin D studies either are on animals or were conducted in small groups of people. Most important, 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, notes George Washington University. 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 can, may, and definitely won’t do for your health.

• 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, according to the NIH. 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, says the 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, but an inadequate level of vitamin D from lack of sun exposure or diet can affect children anywhere in the world, research shows. According to the Mayo Clinic, signs and symptoms of rickets include pain in the spine, pelvis, and legs, as well as delayed growth and muscle weakness. 
  • Meanwhile, osteomalacia refers to 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 present symptoms in its early stages, the Mayo Clinic notes. 
  • Osteoporosis is one of the main causes of fractures and broken bones in older adults. The Mayo Clinic says that 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. Yet observational research has prompted a reexamination of that wisdom. The New England Journal of Medicine study aimed to see if 2,000 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. 
  • An additional review of more than 81 clinical trials, published in October 2018 in The Lancet Diabetes & Endocrinology, found that vitamin D supplements don’t prevent fractures or falls, or have any clinically meaningful effect on bone mineral density. One thing to note: The researchers excluded the treatment of rickets and osteomalacia from their conclusions about the benefits of supplementation. 
• 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, or seasonal depression, according to the National Institute of Mental Health. 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, notes World Psychiatry. Foroutan points out that healthcare providers may prescribe vitamin D supplements to help treat seasonal affective disorder.
  • Studies on the effectiveness of vitamin D as a depression treatment have had mixed results, but a recent one shows promise. A review and meta-analysis published in July 2022 in Critical Reviews in Food Science and Nutrition found that daily vitamin D supplementation equal to or exceeding 2,000 IU per day may help reduce depressive symptoms. However, researchers described their results as having “very low certainty.” 
  • A previous study came to a conflicting conclusion. The research, published in August 2020 in JAMA, found no significant difference in depression symptom frequency between participants who took vitamin D and those who didn’t.
• It Can Protect Against Respiratory Infections
  • Increase your level of vitamin D if you’re deficient, and you may find that you get fewer respiratory infections (aka 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, published in 2022 in the journal Expert Review of Anti-Infective Therapy, found that supplementing with vitamin D may protect against negative outcomes related to COVID-19, although additional research is needed. 
  • One review of 25 randomized, controlled trials involving about 11,300 people suggests that participants who were vitamin D deficient saw a 12 percent reduced risk for respiratory infections after taking a vitamin D supplement, though not every study saw a clear benefit from supplementation. Researchers published their findings in February 2017 in The BMJ. 
  • The main limitations? Researchers weren’t sure whether participants had received a flu vaccine or were diagnosed with the respiratory ailment chronic obstructive pulmonary disease, which are two confounding factors that may have skewed the results.
  • An accompanying editorial also published in The BMJ cautions readers to take the findings with a grain of salt, and the authors argue against standard year-round vitamin D supplementation and call for additional research. 
• It May Help Protect Against Heart Disease and Stroke
  • Is vitamin D heart-healthy? A review of 19 studies linked adequate vitamin D to a reduced risk of heart disease, stroke, and heart failure, although it did not establish whether vitamin D alone was responsible for that outcome. Yet a study published in May 2022 in the American Journal of Clinical Nutrition 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 in June 2022 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, the VITAL study, a randomized clinical trial involving more than 25,000 participants, published in January 2019 The New England Journal of Medicine, found no risk reduction for strokes, heart attacks, or cardiovascular deaths in people who took 2,000 IU supplements daily. 
• It Could Reduce the Risk for Type 2 Diabetes
  • Observational studies in cell models suggest 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 manage type 2 diabetes.
  • But vitamin D supplementation was not found to lower the risk of developing type 2 diabetes in a randomized, controlled clinical trial involving more than 2,400 participants that was published in August 2019 in The New England Journal of Medicine, despite prior observational studies suggesting that it could. A dose of 4,000 IU of vitamin D per day did not significantly lower the risk of diabetes compared with a placebo. The study subjects had a high risk of developing type 2 diabetes but were not necessarily D deficient. In a study published in 2022 in The BMJ, vitamin D supplements also 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. 
• It Plays a Role in Reducing Cancer Death
  • Scientists are paying increasing attention to vitamin D’s possible role in warding off cancer. A review of 63 observational studies that analyzed the potential connection between vitamin D and breast cancer, colon cancer, ovarian cancer, and prostate cancer yielded promising results, suggesting that vitamin D may be an easy and low-cost way to help reduce cancer risk. 
  • The VITAL study also looked at the effect of vitamin D supplements on cancer. The nutrient was not found to reduce the risk of cancer overall for participants. Yet those who developed cancer had a 25 percent lower death rate when they were taking vitamin D. The findings also pointed to a possible reduction in cancer risk for African Americans, though the researchers say that further study is needed. A small study published in July 2022 in Cancer also found low vitamin D levels in Black and Latina women to be linked to an increased risk of breast cancer.
  • 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.
• It May Help Prevent Cognitive Decline and Dementia
  • Foroutan 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 published in April 2022 in The American Journal of Clinical Nutrition linked vitamin D deficiency with an increased risk of dementia and justified its causal effect on the condition. Another research article suggests that vitamin D may help clear up amyloid plaque, the hallmark of Alzheimer’s disease (the most common form of dementia). The authors note that more research is needed to confirm a cause-and-effect relationship between an adequate level of vitamin D and Alzheimer’s specifically. 
  • Meanwhile, a large review published in July 2018 in Nutritional Neuroscience found insufficient evidence that vitamin D supplements protect against neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease. Researchers wrote that they also couldn’t confirm that vitamin D synthesized from sun exposure helps protect against neurodegenerative diseases. 
• 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, according to the Harvard T.H. Chan School of Public Health. To confirm its role, more research is needed, but a study published in 2022 in The BMJ made some significant headway. Among nearly 26,000 participants, 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.

What Vitamin D Definitely Won’t Do for Your Health

By now, you realize that scientists are still exploring how exactly vitamin D affects our bodies and what role it might have in disease treatment and prevention. But one thing’s for sure: Vitamin D is no cure-all, so don’t start taking supplements with the hope that all your health woes will vanish. There’s no vitamin that can do that.

The Takeaway on Vitamin D and Your Health

Vitamin D is an essential nutrient that can help fortify bones and keep them strong while also potentially lowering the risk of cancer and death from cancer for some individuals. But its other effects need to be further investigated before scientists, doctors, and everyone else can make informed decisions about supplementing or upping dietary intake of the vitamin.

Until then, take steps 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.