A Popular Vitamin May Interfere With Cancer Treatment

September 14, 2026

Close-up of a patient pouring large vitamin capsules from a bottle into their hand

Vitamin supplements, including vitamin B3, are often promoted for healthy aging. Claims range from boosting energy to helping repair cells. But new research from University Hospitals suggests that people being treated for pancreatic cancer should use vitamin B3 supplements with caution.

In the study, three common forms of vitamin B3 fueled pancreatic tumor growth and made chemotherapy less effective. “These findings do offer a warning sign that we need to be cautious when taking some supplements,” says Jordan Winter, MD, a cancer surgeon who studies why some tumors resist treatment. “In a healthy individual they can be helpful, but in someone with pancreatic cancer they could actually cause unintended harm.”

The research was done in human cells and mice, not people. More research is needed, but the findings suggest that people being treated for cancer should talk with their doctor before taking supplements.

What Helps Healthy Cells May Also Help Cancer Cells

The body turns vitamin B3 into nicotinamide adenine dinucleotide, or NAD, a substance that helps cells make energy and repair damaged DNA. Vitamin B3 supplements are often sold as nicotinamide mononucleotide (NMN), nicotinamide (NAM) and nicotinamide riboside (NR).

NAD levels drop with age, so these supplements have gained attention for their role in healthy aging. But Dr. Winter wanted to know if something that helps healthy cells could also help cancer cells grow.

“Cancer cells are under enormous stress,” explains Dr. Winter. “They need to constantly repair their DNA to survive.” In other words, the qualities that make vitamin B3 supplements effective for aging cells could bring the same benefits to cancer cells and make them more resistant to treatment.

Dr. Winter’s research found this effect in human cells grown in a lab and in mice with pancreatic cancer. Tumors exposed to vitamin B3 grew more and were more resistant to chemotherapy. Chemotherapy works by damaging the DNA of cancer cells. That’s why a supplement that strengthens a cell’s ability to repair that damage may work against chemotherapy treatment.

What This Means, Whether or Not You Have Cancer

For people without a cancer diagnosis, Dr. Winter believes that the evidence supporting the benefits of vitamin B3 outweighs the risks uncovered by the study.

“At any given moment, the odds that a person has an undiagnosed cancer are low,” he says. “That means for people who aren’t diagnosed with cancer, it may be more important to support healthy cells with supplements such as vitamin B3.” It’s also important to note that large clinical trials have not been done to support the long-term benefits of these supplements for longevity or disease prevention.

For those with a cancer diagnosis, the results of the study do suggest having a careful conversation with your oncologist. The study did not examine the effects in human patients, and is unlikely to, since researchers would not give people a supplement they believe could cause harm. And the results were limited to pancreatic cancer. Still, Dr. Winter says, “Based on our findings, I would be very cautious about taking vitamin B3 supplements if you have cancer, especially if you are receiving chemotherapy.”

A Broader Caution About Supplements

Another useful takeaway from Dr. Winter’s research? “A supplement that can be beneficial in one context can be counterproductive in another,” he says. Dr. Winter’s team is now investigating whether other supplements that support DNA repair could have comparable effects on cancer cells.

Overall, when considering any supplement, keep in mind that “natural” and “over the counter” don’t necessarily mean harmless in every situation. Beyond emerging research like Dr. Winter’s examining the relationship between supplements and cancer cells, certain supplements can also interact with common prescription drugs and even other supplements. If you’re considering adding a supplement to your regimen, talk to your doctor first to make sure that daily capsule is more likely to help your health than harm it.