By Stacey Butterfield
David Seres, MD, sees his concerns about dietary supplements as part of a larger problem: “the war on truth and the war on science,” as he put it during Internal Medicine Meeting 2025's Tuesday precourse, “Advancing Nutrition in Medical Practice."
During his talk, Dr. Seres reviewed the science (or lack thereof) underlying manufacturers' claims for some supplements, including those that purport “to improve" brain and prostate health. The claims are phrased that way to avoid falling under FDA jurisdiction, noted Dr. Seres, who is a professor of medicine in the Institute of Human Nutrition at Columbia University Medical Center in New York.
“They cannot claim to treat or prevent or diagnose a disease,” he said. “But why are people taking supplements if it's not to treat or prevent a disease, right?” And they definitely are taking them—Dr. Seres cited one estimate that put the value of the global supplement market at more than $190 billion in 2024.
Given how much the industry spends on advertising, Dr. Seres assumed that his audience had already heard about apoaequorin, a protein that is found in jellyfish, binds to calcium, and has been alleged to affect memory.
“What about the fact that you don't get proteins out of your intestine and into the bloodstream intact? They are digested, right? And even if you've gotten it into the bloodstream, anybody ever hear of the blood-brain barrier?” he said.
The manufacturer of an apoaequorin supplement cites a randomized controlled trial to support its use, but in fact, the overall results didn't show any effect, Dr. Seres said. “If you do enough post hoc analyses, you will find something, and that's what they did. With 30 post hoc analyses, they found that in one subgroup, [supplement users] actually scored better on one of the subscores,” he said. “But that's not valid science.”
The manufacturer has since been sued, including by the Federal Trade Commission, for whom Dr. Seres has consulted, and the claims have been revised to say that the supplement works on calcium in the gut, he reported.
Moving to the prostate, Dr. Seres tackled the evidence on supplements with vitamin E and selenium.
“How do you get into trouble with observational research? Men who have prostate cancer have low selenium and vitamin E levels, thus, men should receive selenium and vitamin D supplementation to prevent prostate cancer,” said Dr. Seres. “Well, that's an interesting thought.”
However, the hypothesis was disproven by the Selenium and Vitamin E Cancer Prevention Trial (SELECT), a randomized controlled trial of both supplements that included more than 30,000 men and was published by JAMA in 2011.
“There was a 17% statistically significant increase in prostate cancer over 10 years in those who received vitamin E,” reported Dr. Seres. The rate of prostate cancer was not significantly different with selenium versus placebo, the trial found.
Another nutrient that has been viewed as a preventive for prostate cancer is lycopene. “Do you guys remember ‘Eat tomatoes, you won't have prostate cancer’?” asked Dr. Seres. “Well, there were a couple of observational studies [that showed an] association, but read your literature carefully, please.”
The research on lycopene was observational, he explained, and when a trial, published by The Prostate in 2015, tested dietary supplements containing lycopene, selenium, and green tea catechins in men who had been treated for prostate cancer or precancerous lesions, they were more likely to have cancer on subsequent biopsies than those who got placebo.
Speaking of green tea extract, Dr. Seres offered his concerns about that, too. “People who drink green tea culturally drink it sort of constantly and sip 12 cups a day, and that is associated with a lower weight. There are lots of reasons why that may be,” he said.
In an effort to mimic those effects, supplement manufacturers have put the catechins one would get from 12 cups of tea into a single pill. “And if you know anything about toxicity levels, you know little bumps might not be a problem, whereas one big bump might exceed toxicity levels,” he said.
The toxicity of green tea supplements has not been definitively proven, but it's “a large concern” and should be studied, according to Dr. Seres.
Other supplements that have been studied and found to potentially harm patients include B vitamins, which were tied to higher lung cancer risk in men in a trial published by the Journal of Clinical Oncology in 2017. And antioxidants, specifically beta-carotene, were associated with higher mortality, according to a systematic review published by JAMA in 2007 that didn't break results down by sex.
These results are evidence of the need for more research and regulation regarding supplements, according to Dr. Seres. He noted that he actually takes a B12 supplement because lab tests showed he was deficient, and his concern is about the broad use of supplements.
“We regulate everything else. Why are we not willing to regulate these?” he said. “Dietary supplements in general are likely to have no effect or minimal salutary effects, if at all. They may be harmful, and they are deregulated and treated as if they were an apple and not a drug.” ■