A new review published in The Lancet suggests that vitamin D supplementation does not offer significant protection against developing acute respiratory infections — the coughing, sneezing, and runny nose typically associated with a cold.
Vitamin D is the second most commonly used dietary supplement in the U.S. after multivitamins, according to the Centers for Disease Control and Prevention. Many believe that supplementing with this fat-soluble nutrient — found in a limited number of foods and easily absorbed from sunlight — plays a key role in warding off everyday illnesses.
Historically, there was some scientific support for this belief. For instance, a 2021 meta-analysis conducted by the same group of researchers found a “modest protective effect” from taking daily vitamin D to prevent respiratory infections.
In this latest study, researchers revisited the evidence, this time incorporating more recently published data.
“There’s lots of evidence that vitamin D influences the immune system, and many people have low vitamin D levels,” study author Carlos A. Carmago, Jr., MD, professor of epidemiology at Harvard T.H. Chan School of Public Health, told Health. He added, “Would giving a vitamin D supplement help?”
The Latest Findings on Vitamin D and the Common Cold
For this updated systematic review and meta-analysis, Carmago and his team added six new studies, bringing the total to 46 studies with over 64,000 participants.
They assessed whether vitamin D supplementation reduced the risk of acute respiratory infections compared to a placebo, and also looked at factors like age, dosage, and baseline vitamin D levels. Their analysis used a statistical technique known as a random-effects model.
The outcome? Vitamin D supplementation did not significantly decrease the likelihood of contracting a cold, regardless of age, dosage, or initial vitamin D status. (The good news is that vitamin D did not lead to more side effects compared to a placebo.)
Pulmonologist Neil W. Schluger, MD, dean of the School of Medicine at New York Medical College, who was not involved with the study, said these findings are not unexpected.
“Although the prior (2021) review suggested a small benefit in preventing acute respiratory tract infections from vitamin D supplementation, that finding just barely reached statistical significance,” he noted in an email. “With the addition of several large, recent randomized controlled trials to the review, there is no longer evidence of a statistically or clinically significant reduction in the risk of acute respiratory infection (common colds but also bronchitis and pneumonia) in persons taking supplementation.”
Schluger further commented that despite the widespread public interest in vitamin D for respiratory illness, the most comprehensive and well-designed trials have not shown clear benefits for this use.
Carmago emphasized that vitamin D’s effects on respiratory infections are not straightforward. “Looking at all vitamin D regimens as one intervention is challenging,” he explained. Individuals with low vitamin D levels at baseline might benefit from frequent, low-dose supplementation, but if others do not, it skews the overall results toward the “null,” making the findings statistically insignificant.
“Many people want to know if vitamin D supplements ‘work’ as a yes or no question—but the answer is ‘it depends,’” he said.
What to Consider Before Taking Vitamin D
Even though vitamin D might not be a magic bullet for preventing colds, maintaining adequate levels remains essential for good health. Vitamin D plays a critical role not only in immune function but also in bone and neuromuscular health and reducing inflammation.
While it’s wise to consult with your healthcare provider about whether vitamin D supplementation is appropriate for you, Darby said that certain groups may benefit. For instance, individuals living in areas with limited sunlight exposure may be at higher risk of vitamin D deficiency. Additionally, those with osteoporosis might require extra vitamin D.
You can also improve your intake through food. “Most people can reach their vitamin D needs with fortified foods,” Darby noted, stressing the importance of paying attention to overall diet quality and variety. Fortified milk, cereal, orange juice, breads, and naturally rich sources like fatty fish can all contribute.
Evidence-Based Ways to Prevent a Cold
There is no guaranteed way to prevent respiratory infections, but certain habits can enhance your immune system’s resilience.
“Maintaining a healthy diet, avoiding tobacco use, and staying up to date on recommended vaccinations for viruses and bacteria that cause pneumonia are the best ways to avoid respiratory infections,” Schluger said.
As for relying heavily on supplements, he advises caution. “Many people take vitamins and supplements, but there is little evidence for health benefits of any kind unless a physician has identified a specific vitamin deficiency.”
Great article.