Do Vitamin D Supplements Help Prevent Cancer?

Vitamin D, referred to as the “sunshine vitamin,” is routinely in and out of the spotlight. While it’s true the vitamin can support bone health and immune health, it’s less certain that it can reduce the risk and severity of a COVID-19 infection—though that’s something researchers have spent a great deal of time exploring.

Similarly, a great deal of research has been dedicated to the role of vitamin D in cancer prevention and progression, though there’s not much by way of definitive answers.

Here’s what you may be hearing about, and how research does—and does not—support those claims.

Vitamin D and Cancer Prevention

People with more frequent sun exposure tend to have a lower risk of vitamin D deficiency and a lower risk of getting cancer. Plus, studies have reported lower cancer and cardiovascular deaths in regions with greater sun exposure. With that in mind, could a vitamin D supplement help stave off cancer in people who don’t see the sun as much?

JoAnn E. Manson, MD, DrPH, chief of the division of preventive medicine at Brigham and Women’s Hospital in Boston, is not so convinced. She explained people with lower cancer risk tend to be more active, and therefore spend more time outdoors. As a result, their vitamin D levels are often higher, since the body creates vitamin D3 after absorbing UVB light from the sun.

“Vitamin D level is a marker for other factors that are related to cancer,” Manson told Verywell, adding that it’s not a direct indicator of cancer risk.

Plus, Manson has learned through her own research that the data supporting the use of vitamin D supplements to prevent cancer is not incredibly strong.

Among the sparse data regarding vitamin D supplementation and cancer risk, a 2019 study published in the New England Journal of Medicine led by Manson is perhaps one of the most well-designed. This study evaluated whether vitamin D supplementation impacted cancer incidence. Called The VITamin D and OmegA-3 TriaL (VITAL), this randomized, placebo-controlled trial assessed whether a 2,000 IU per day dose of vitamin D3 and a gram per day of marine omega-3 fatty acids impacted cancer risk.

After evaluating over 25,000 subjects, the researchers didn’t find a strong relationship between vitamin D supplementation and cancer incidence.

“The research on vitamin D supplements to prevent cancer is inconclusive,” Sarah Anzlovar, MS, RDN, LDN, an intuitive eating dietitian at Sarah Gold Nutrition, LLC, told Verywell. She explained that if a person is deficient in this nutrient, supplements can help them achieve adequate blood levels, which is important for many health outcomes. But if a person is not deficient in vitamin D, there’s little to no benefit to taking supplements. In fact, too much vitamin D can actually be harmful.

Data does exist that suggests healthy vitamin D levels may be linked to a reduced risk of two specific cancers: colorectal and bladder. But more data is needed to make a firm recommendation. 

Vitamin D and Cancer Progression

Very few studies have reported on vitamin D supplementation and cancer outcomes, whether a specific type of cancer or cancer in general. However, Manson says the data that does exist is strong.

Specifically, Manson said results of the VITAL trial show supplementation with 2,000 IU of vitamin D is associated with a 17% reduction of advanced cancers.

Other data shows positive outcomes as well, although the relationship is not incredibly strong. A Cochrane Systematic Review reported lower overall cancer mortality with vitamin D supplementation but concluded that the finding could be due to chance. And a study evaluating over 25,000 people showed that vitamin D3 supplementation might reduce the risk of developing advanced cancer among adults with certain cancers. In the same study, for those diagnosed with breast cancer, vitamin D supplement use was associated with higher levels of self-reported quality of life.

Should You Take Vitamin D Supplements?

While having adequate vitamin D in the body is linked to a slew of benefits, and bears repeating that you shouldn’t rely on it to prevent cancer.

“Vitamin D should not be used as a standalone line of defense against cancer,” nutrition consultant Liz Shaw, MS, RDN, told Verywell. “Given that the etiology of cancer is unique for every individual who receives this diagnosis, it’s important to take a multifaceted approach to lower one’s risk for developing cancer. There is a genetic component to cancer as well—genes may play a significant role in development and progression.”

Both Shaw and Manson said healthy lifestyle habits, like a well-balanced diet, regular exercise, plenty of sleep, and sunscreen use are most important for cancer prevention.

“At least 50% of cancers are preventable by healthy lifestyle behaviors,” Manson shared. “People can’t throw a vitamin D supplement at an unhealthy diet and lifestyle.”