By Molly Knudsen, M.S., RDN on April 19, 2026. Knudsen is a Registered Dietitian Nutritionist.
Colon cancer rates are rising, particularly among younger adults. While age remains a factor, environmental and lifestyle elements can influence its development. Data show that about half of colon cancer cases may be prevented through lifestyle changes.
Focusing on vitamin D status is important. Decades of research suggest vitamin D might protect against colorectal cancers, and low levels are a risk factor.
To understand this relationship, researchers recently analyzed data from 50 studies involving over 1.3 million participants to examine vitamin D’s role in colorectal cancer prevention.
Vitamin D and Cancer Risk
The review found that low vitamin D levels are strongly associated with a higher risk of colorectal cancer.
One meta analysis showed that people with higher vitamin D levels, measured by blood test, had a 39% lower risk of colorectal cancer compared to those with lower levels. When levels were tracked over time, higher vitamin D was linked to a 20% reduced risk.
A study from 1996 found that women with the highest vitamin D intake were 58% less likely to develop colorectal cancer than those with the lowest intake.
In the Danish “Diet, Cancer and Health” study, vitamin D appeared to offer enhanced protection against colon cancer risk for individuals with a genetic predisposition.
The Iowa Women’s Health Study indicated that women who took calcium and vitamin D supplements had a 15% lower risk of developing colorectal cancer compared to non users.
Another study found that increasing vitamin D intake reduced the risk of adenomas, which are polyps that could become cancerous.
A Canadian study reported that vitamin D supplements reduced the risk of polyps by 33% and high risk polyps by 43%.
How Vitamin D Might Protect
While many studies in the review showed protective benefits, most did not identify exact mechanisms. However, laboratory, animal, and other human studies suggest that the active form of vitamin D, calcitriol, may target colon cancer progression in several ways.
These include slowing cancer cell growth, triggering cell death, supporting a balanced gut microbiome, maintaining healthy intestinal cells, and reducing gut inflammation.
Low Levels Are Common
Vitamin D can aid immunity, mood, and cellular health, but most people have low levels. A 2025 study of over 5,600 U.S. adults examined vitamin D levels and muscle mass, finding that 42% were vitamin D deficient, with blood levels below 20 ng/mL.
Another 37.6% had insufficiency, with levels between 20 and 30 ng/mL. Only about 20% had sufficient levels of 30 ng/mL or higher. This means nearly 80% of adults had low vitamin D.
Researchers emphasized the importance of maintaining vitamin D levels between 30 and 40 ng/mL, and noted that many could benefit from levels around 50 ng/mL.
Increasing Vitamin D
Vitamin D is found naturally in foods like cod liver oil, trout, and salmon, and in fortified items such as milk and eggs. However, many people, especially those with low levels, may benefit from a high quality vitamin D supplement.
A general guideline is to look for supplements providing 2,000 to 5,000 IU of vitamin D3, taken daily. Levels typically begin to improve within a few months.
Vitamin D status is one lifestyle factor connected to colorectal cancer risk that can be improved with supplementation. Other habits can further reduce risk, and regular screenings starting at age 45 are important for early detection and treatment.
The review cited multiple sources, including studies from journals and health databases, to support these findings.
