A new review of research suggests that maintaining adequate vitamin D levels may help lower a person’s risk of developing colorectal cancer. The findings come as colon cancer rates are rising, particularly among younger adults.
Researchers analyzed data from 50 studies involving more than 1.3 million participants to understand the link between vitamin D and colorectal cancer prevention. They found that low levels of the vitamin are strongly associated with a higher risk of the disease.
Key Study Findings
One major analysis showed that people with higher blood levels of vitamin D had a 39% lower risk of colorectal cancer compared to those with lower levels. Another long-term study found that tracking vitamin D levels over time linked higher levels with a 20% reduced cancer risk.
A landmark study from 1996 found that women with the highest dietary vitamin D intake were 58% less likely to develop colorectal cancer than those with the lowest intake. Other research indicates the vitamin may offer enhanced protection for individuals with a genetic predisposition to the disease.
In the Iowa Women’s Health Study, women who took calcium and vitamin D supplements had a 15% lower risk of developing colorectal cancer. Separate research has shown that increasing vitamin D intake can reduce the risk of precancerous adenomas, or polyps. A Canadian study found supplements reduced polyp risk by 33% and high-risk polyp risk by 43%.
How Vitamin D May Work
While the exact mechanisms are still being studied, laboratory and animal research suggests the active form of vitamin D in the body, calcitriol, may combat cancer progression in several ways. These include slowing the growth of cancer cells, triggering cell death, supporting a balanced gut microbiome, maintaining healthy intestinal cells, and reducing inflammation in the gut.
Widespread Deficiency
Despite its potential benefits, vitamin D deficiency is common. A 2025 study of over 5,600 U.S. adults found that 42% were deficient, meaning they had blood levels below 20 nanograms per milliliter. Another 37.6% had insufficient levels between 20 and 30 ng/mL. Only about 20% of participants had sufficient levels. This means nearly 80% of the adults studied had low vitamin D.
Researchers emphasize that maintaining blood levels between 30 and 40 ng/mL is important, and many people could benefit from levels around 50 ng/mL.
Increasing Vitamin D Levels
Vitamin D is naturally present in some foods like fatty fish, including trout and salmon, and cod liver oil. It is also added to fortified foods like milk and eggs. However, many people, especially those with low levels, may benefit from a supplement.
A general guideline is to look for supplements providing 2,000 to 5,000 International Units (IU) of vitamin D3, taken daily. Levels can begin to improve within a few months of consistent supplementation. Healthcare professionals also recommend regular screenings for colorectal cancer, starting at age 45, for early detection and treatment.
