Curcumin isn't the only chemical compound in turmeric; it's one of hundreds. But fans say it can brighten skin, lift spirits and maybe even fight cancer.
On the surface, the claims don't seem outlandish: After all, turmeric has been used in India's Ayurvedic medicine as an anti-inflammatory, cough suppressant and cure-all for thousands of years. But Western researchers are divided on the efficacy of the herb and its best-known compound.
Ajay Goel, a cancer researcher and director of Baylor University's Center for Gastrointestinal Research, has been intrigued by curcumin's potential as an anti-inflammatory for decades. He believes that curcumin treatment will one day become mainstream.
Goel has studied curcumin's potential effectiveness on everything from cancer and rheumatoid arthritis. In a pilot study whose results were published in 2012, Goel reported that rheumatoid arthritis patients who took curcumin for two months reported less joint swelling and tenderness than those who took a common anti-inflammatory drug. His 2013 study of the compound's effects on colorectal cancer cells in the lab suggests it makes chemotherapy drugs more effective. When Goel gave curcumin to a small group of patients with major depressive disorder, they reported experiencing reduced symptoms — results nearly on par with people who took a generic form of Prozac. And, Goel says, it's "a very safe, effective natural compound."
But how effective? Studies are often done in test tubes, on animals or with small groups of people. And Goel says that researchers haven't yet settled on a standard therapeutic dose. That hasn't stopped them from studying it: More than 10,000 studies and more than 120 clinical trials have assessed both the herb and the compound.
Kathryn M. Nelson, a principal scientist at the University of Minnesota's Institute for Therapeutics Discovery and Development, is more skeptical. In January, she and colleagues published a review of curcumin's chemistry in the Journal of Medicinal Chemistry that raised questions about curcumin's therapeutic potential.
Curcumin's bioavailability — the amount that makes its way throughout the body — is "dismal," Nelson says. The chemical is fragile, and once it's ingested, it's quickly excreted. "The compound itself is probably not doing anything," she adds. "It falls apart in water. Think about how well it's going to survive your stomach" and its acids.
If turmeric does have benefits, Nelson suggests, curcumin may not be the compound that delivers them. "There are things that can fool you into thinking a compound is active when it's not," she says. (Active compounds are ones that have an actual effect on the body.) She notes that many studies mix curcumin with oils or other substances and that clinical trials are inconsistent in how they use the compound.
Given the historical and anecdotal evidence, Nelson says, there may be benefits to turmeric, but she doesn't think curcumin and its relatives, curcuminoids, are causing them.
Goel — who serves on the scientific advisory board of Terry Naturally Vitamins, which produces supplements that include curcumin — and other researchers disagree.
"Does this thing work? Absolutely. Does it work amazingly for every single person? No," Goel says. The authors of the January review "have no understanding of the topic."
However, research on the benefits of turmeric and curcumin is anything but settled. According to the National Institutes of Health's National Center for Complementary and Integrative Health, "claims that curcuminoids found in turmeric help to reduce inflammation aren't supported by strong studies" and studies on possible uses are "preliminary." And last year, a scandal related to curcumin research further shook confidence in the compound.
In March 2016, Bharat Aggarwal, a cancer researcher and one of curcumin's most-cited boosters, retired from MD Anderson Cancer Center after the center began an investigation into whether his research data and images had been manipulated. Several journals issued retractions of Aggarwal studies. His attorney at the time was quoted saying that any problems were "some minor mistakes" and that his client was retiring simply to pursue other endeavors.
All told, 18 of his papers — six dealt with curcumin and its impact on cancer — were retracted by scientific journals.
Goel co-authored six papers with Aggarwal, but none of those have been retracted. "He is one of those who contributed significantly to the field," Goel says, "but not the only one."
Nelson says it's time to move on from curcumin. "Maybe we should stop putting so much effort into this one chemical structure," she says. With hundreds of other compounds in turmeric, there's plenty for scientists to study, she says.
Goel is sticking with curcumin, though. "Curcumin has several challenges," he admits. It's poorly absorbed and does not show up in blood, but he says that blood concentrations may not matter. He says researchers should focus on the products created when curcumin is metabolized. "It is reasonably safe," he adds — "at least worth trying."
But even that is up for debate. In March, an Encinitas, Calif., woman died, reportedly of an adverse reaction after getting an "infused turmeric solution" through an IV to treat her eczema flare-ups. And a recent report in the New York Times suggests that use of turmeric and curcumin — which have known but not well-studied blood-thinning effects — may have interacted adversely with anticoagulant drugs that a man was taking.
Gregory Cole, who leads UCLA's Mary S. Easton Center for Alzheimer's Disease Research and has studied curcumin's possible effects on Alzheimer's, says that consumers should proceed with caution but that there's still hope for researchers who have poured time and resources into curcumin.
"There's promise," he says, "but it's early." Cole, who said he receives a small annual royalty for a curcumin formulation he developed, thinks it's unlikely that curcumin will find its way into the mainstream until a government or large pharmaceutical company funds more research. Until then, he says, people "need to be aware that it's a drug. The issue of what dose to take is something we just don't understand yet."
The controversies and uncertainties probably won't stop turmeric's rise. The American Botanical Council, whose members include supplement manufacturers, says turmeric was the top-selling herbal dietary supplement in natural- and health-food stores in 2015. But for consumers attracted by turmeric and curcumin's long list ofsupposed benefits, all that gold may not yet glitter.