As Probiotic Labels Tout Benefits, A Call To Examine Risks

They promise to improve immune health, bolster intestinal health, "support vaginal health," even help us cope with stress and restore our "natural balance" of bacteria.

Such rosy claims crop up in the pharmacy vitamin aisle, the supermarket yogurt section, the kombucha cooler and wherever else probiotics are sold.

Companies promise the benefits of "good bacteria" — but a leading medical watchdog says we should be questioning some of those claims, and looking at the risks. 

Dr. Pieter Cohen of Harvard Medical School and Cambridge Health Alliance has raised red flags in the past about the quality and claims of supplements — vitamins, herbs, all sorts of substances sold to improve health but regulated far, far less than medical treatments.

Now, he warns in a JAMA Internal Medicine piece titled "Probiotic Safety — No Guarantees" that probiotics face similar issues. In fact, "probiotics" itself may be a misnomer. Because they are defined as microorganisms that confer a health benefit, it may be better to call them "live microbials," Cohen says.

The Food and Drug Administration is currently considering new rules for probiotics; Cohen argues that Canada has already made a good start on probiotic regulation that the United States may want to emulate.

Here are some key points he raised in an interview:

Quality Assurance

There's a basic lack of quality control to the point that some products basically do nothing, Cohen says: "Because of storage problems, and because of quality control problems, the number of bacteria or yeast are low or relatively low when someone takes it, and the other question is whether it actually colonizes the gut, which is controversial. What we're worried about though is that there might be risks that are poorly understood."


Cohen cites the tragic death of a newborn in Connecticut back in 2014 who died after being treated with probiotics. The CDC reported the cause of death as a fungal contamination of a probiotic supplement. There's no good system to track these cases, Cohen says, but there have been dozens of reports of bacteria that were supposed to be benevolent but actually acted more like infections in the people who took them. The bad reactions were mainly in people with compromised immune systems.

Healthy People

In terms of solid, peer-reviewed evidence, Cohen says, the benefits for healthy people are pretty much only hypothetical at this point.

"There's no long-term large study, certainly never one that's been duplicated, which has demonstrated: you take a healthy person, and you give them probiotics, and you somehow prevent illness or make them healthier. That doesn't exist. Despite that there's been a lot of hype about why people should take their probiotics. But there hasn't been a discussion about the potential risks."

Jumping Genes?

Another potential risk Cohen mentions, that still needs to be explored, is whether probiotics could actually worsen the looming problem of bugs that are resistant to antibiotics — because it’s possible that some probiotics sold here could have the type of antibiotic resistance genes that can sort of jump from one bacteria to another, and no one is making sure they don’t.

But Isn't Fermented Food Good For Us?

While probiotic supplements are new, humans have been eating and drinking fermented substances like ayran, kefir and kimchi for many millennia. Overall, they are supposed to be good for us. Dr. Cohen draws a parallel between probiotic supplements and vitamins: Taking some vitamin C does not have the same health benefits as eating an orange. And taking a supplement with one strain of bacteria that's the same as, say, what grows in kimchi is not the same as the whole complex explosion of ingredients in the Korean fermented vegetable dish.

So, Never?

Not necessarily never. Clearly much more research needs to be done. But Dr. Cohen says even at this point, there are a couple of cases where published studies make it reasonable for doctors to prescribe probiotics:

• Adults who are at very high risk for a dangerous infection called C. difficile that antibiotics can trigger, who are being prescribed a new course of antibiotics.

• Children who tend to get bad diarrhea when taking antibiotics."But when we say probiotic, that doesn't mean anything on the store shelves. That will mean talk to your doctor about which strain of probiotic you should be taking."

Strain, Type, Number

Part of the problem is that the labels on American probiotics might tell you the very broad type of bacteria they are — like lactobacillus or bifidobacteria --- but not necessarily which strain. Cohen says that you need to know the strain to be able to look up the most relevant research on the effects it has.

Also, the FDA recently proposed that probiotics makers have the option — but not the requirement — to put on the label how many live organisms a dose actually contains. The Canadians are already ahead of us on probiotic regulation, Cohen says: They require the strain and the number of live organisms on the label, and they better monitor for the potential that the bacteria could spread antibiotic resistance.

What To Do For Now?

At the very least, confer with your doctor and let your doctor know what you're taking, Cohen says. And don't buy all the claims you see on those bottles: Probiotics are very similar to other supplements in that, because of a 1994 law, they can make claims that they improve human health so long as they stay away from claiming to prevent or cure a specific disease.

So if they stay vague — like "This will promote intestinal health" or "boost your immune system" --- they can put that on the label, Cohen says, "even if the only evidence you have is one small study in a petri dish of one of the ingredients in your supplement, and larger studies in either animals or humans has already proven that it doesn't work."

Headshot of Carey Goldberg

Carey Goldberg Editor, CommonHealth
Carey Goldberg is the editor of WBUR's CommonHealth section.



More from WBUR

Listen Live