A 2005 study found that women with higher blood levels of vitamin B6 had a lower rate of colon cancer. The finding was worth studying, but it did not show that taking vitamin B6 prevents cancer. Later research makes that distinction especially important: a randomized trial of a combination containing vitamin B6 did not reduce colorectal polyps.
This article was updated in October 2026 to link the original research directly and put the early result in context. The original study is Plasma vitamin B6 and the risk of colorectal cancer and adenoma in women.
What the 2005 study actually measured
Researchers used blood samples from 32,826 women in the Nurses' Health Study. The samples were collected in 1989 and 1990. The team measured pyridoxal 5'-phosphate, or PLP, the main active form of vitamin B6 circulating in blood. They then identified 194 colorectal cancer cases through 2000 and 410 colorectal adenoma cases through 1998. Adenomas are growths that can sometimes develop into cancer.
The researchers compared women with higher and lower PLP levels. For colorectal cancer overall, the group with the highest PLP levels had an estimated 44% lower risk than the group with the lowest levels. The estimate came with a 95% confidence interval that crossed the no-difference line, so this particular comparison was suggestive rather than statistically conclusive. For colon cancer specifically, the estimated relative risk was 0.42, or 58% lower, with a confidence interval from 0.21 to 0.85. The researchers adjusted for several known risk factors, and some estimates changed after additional adjustment for folate, multivitamins, and methionine.
Those percentages compare two groups in one study. They are not the expected benefit of a supplement for an individual. The study observed natural differences in vitamin status; it did not assign one group to take B6 and another to take a placebo. People with higher PLP levels could differ in diet, health, or other ways that the analysis could not fully measure. A blood level can also reflect how the body handles a nutrient, not just how much someone eats.
Did the evidence hold up?
Another analysis of women examined reported intake of folate, B6, and multivitamins. It found no statistically significant link between total B6 intake and colorectal cancer risk (Folate, vitamin B6, multivitamin supplements, and colorectal cancer risk in women). The result does not erase the earlier blood-level finding. It does show why a measured blood marker and a supplement recommendation are different claims.
A more direct test randomly assigned 5,442 female health professionals to a daily pill containing folic acid, 50 mg of B6, and B12, or to a placebo. Among 1,470 participants who later had an endoscopy, colorectal adenomas were found in 24.3% of the treated group and 24.0% of the placebo group. Follow-up extended as long as 9.2 years. The trial found no meaningful difference in this outcome (Effect of combined folic acid, vitamin B6, and vitamin B12 on colorectal adenoma).
The trial has a limit: it tested three nutrients together, so it cannot isolate the effect of B6 alone. It also measured adenomas in the participants who underwent endoscopy, rather than proving anything about lifelong cancer risk. Still, its null result does not support a claim that high-dose B6 supplements prevent colorectal growths. A related randomized trial found no significant reduction in overall invasive cancer from the same B-vitamin combination (Effect of combined folic acid, vitamin B6, and vitamin B12 on cancer risk in women).
What vitamin B6 is for
Vitamin B6 helps the body use protein and supports many normal metabolic processes. Most adults need roughly 1.3 to 1.7 mg a day, depending on age and sex. Foods that provide it include fish, poultry, potatoes, chickpeas, bananas, and fortified cereals. The NIH vitamin B6 fact sheet explains food sources, recommended amounts, and signs of deficiency.
Getting enough of an essential nutrient is sensible. More is not automatically better. High doses of B6 from supplements taken over time can damage nerves, causing numbness, tingling, or trouble with coordination. Older articles often cite a US upper limit of 100 mg a day as if it were a target. It is a ceiling, not a recommended dose, and the European Food Safety Authority set a much lower adult upper limit of 12 mg a day in 2023 because of neuropathy concerns. The NIH health professional fact sheet explains both limits and the evidence behind them. Anyone taking several supplements should check their combined B6 content.
What reduces colorectal cancer risk more reliably?
Screening has far stronger evidence for preventing colorectal cancer deaths than B6 supplementation. The US Preventive Services Task Force recommendation advises screening adults at average risk from age 45 through 75. For ages 76 to 85, the decision depends on health, past screening, and preferences. People with symptoms, a strong family history, prior polyps, or other risk factors may need a different plan with their clinician.
Options include stool-based tests and colonoscopy. A positive stool test needs follow-up colonoscopy. The right test is one a person can complete on the advised schedule. Screening timing and proper follow-up matter more than adding a high-dose vitamin pill.
The practical reading of the vitamin B6 research is modest. The 2005 study raised a biological question. It did not establish a preventive dose, and later randomized evidence has not shown a benefit from a B6-containing supplement combination for colorectal adenomas. Eat a varied diet that supplies enough B6, discuss a suspected deficiency with a clinician, and keep recommended colorectal screening on schedule.
