How turmeric became a naturopathic cure-all without the evidence to back it up

My local grocery store is packed with health supplements that promise to cure every ailment, from upset stomachs to anxiety, without the need to go to the prescription counter. There are similar "natural" health sections in stores nationwide.

And maybe there is nothing wrong with that. As long as people are mindful about how any medications they take may interact with supplements and consult with their primary care doctor first, I’m not against the idea. The problem is, more often than not, even if those supplements don't do harm, they aren't helpful, either. And yes, scientists themselves are partly to blame for overblown expectations of naturopathic medicines.

A prime example of this is curcumin. As of now, PubMed, the biggest US database of biomedical literature, contains over 9,000 original research papers on the compound, which is naturally found in the spice turmeric. Turmeric, or "golden spice", gives yellow curries their distinct color and flavor and has been described in Ayurvedic medicine as a treatment for inflammation.

Dozens of research labs in the US alone have received over $150 million in federal funding to study effects of curcumin in cancer, arthritis, Alzheimer’s, diabetes, depression, and many other conditions. Sales of curcumin supplements in the United States reportedly exceeded $20 million in 2014 and, according to predictions, the global market for curcumin is expected to reach $94.3 million by 2022.

So it's no wonder that a paper published in January of this year, by the University of Minnesota's Dr. Kathryn Nelson and colleagues, arguing that curcumin is not a potential wonder drug was akin to a bomb explosion. It has underscored once more the importance of scientific rigor, thoughtful experimental design and cautious claims and caveats that should accompany every research study.

That's not to say that no natural product ever made it to the global drug market. Aspirin, a component of willow tree bark, and morphine from the opium poppy are drug staples, of course. And a Nobel Prize for Physiology and Medicine was awarded as recently as 2015 for the discovery of artemisinin — a drug isolated from sweet wormwood, an herb used in traditional Chinese medicine, which has now replaced quinine as a new World Health Organization recommended therapy for the first-line treatment of malaria.

Unlike artemisinin, though, curcumin is, as Nelson wrote, more of a “missile that continually blows up on the launch pad, never reaching the atmosphere or its intended target(s).”

For one, curcumin is extremely short-lived in solutions — and it's degraded almost completely within 10 minutes at the body temperature. What’s more, only 1 percent of an ingested curcumin capsule actually gets absorbed into the bloodstream. In comparison, that value for Aspirin is 68 percent. For artemisinin, it's 30 percent. Even in a dose of 12 grams of pure curcumin per day (that’s 24 standard capsules a day or, by a generous estimation, about 44 pounds of turmeric-rich curry) scientists could not detect curcumin in the blood of the majority of clinical trial participants. Some people have, however, experienced diarrhea and headaches.

An ideal prototypical compound that has good chances to become a drug is effective even in low doses and displays a wide toxicity window: the effective dose is orders of magnitude away from the toxic dose. For the pharmaceutical company to be interested in pursuing the costly process of drug development and approval, a potential drug compound has to have a well-defined mechanism of action, be selective, stable and get into the bloodstream quickly and efficiently — none of the qualities displayed by curcumin.

One of the main reasons why curcumin research remains so popular among the scientists is because it keeps giving positive results in the lab. That is, it seems to be effective. But Nelson underscores that curcumin belongs to the class of compounds that often interfere with the techniques used in drug testing procedures. In the paper, she writes that any report "should be treated with caution.”

It’s telling that the first scientific study of curcumin use in patients was published 80 years ago, and no curcumin-based therapy has been approved for the medical application to this day. Clinicaltrials.gov, a publicly available U.S. National Institute of Health database of current and terminated clinical trials, annotates 156 clinical trials on curcumin with over 40% of them completed. Despite that, only eight studies have their results reported and available for everyone to see and judge. Incidentally, those results are either negative or inconclusive because of the poor study design and low number of participants.

Still, the studies make sexy clickbait. One of the most highly cited studies, from 2006, attempted to link curry consumption among the elderly Singaporeans to their cognitive status. According to the study, elderly residents that reported consuming turmeric-rich curry “often” (from once a month to once a day) performed better on a mental state examination test than those who ate curry “rarely or never” (less often than once in six months). While the study authors cautiously emphasized that their results “do not establish a clear and direct causal effect of curry consumption on improving cognitive function,” the research was written up by multiple mainstream outlets. Adjusted for the variability of the cognitive test results, differences between those who favored curry dishes and those who did not turned out to be insignificant.

Another widely cited study compared the risks of Alzheimer's disease among residents of Ballabgarh, a rural village in northern India, to those of rural mid-Monongahela Valley of southwestern Pennsylvania. This work did not even attempt to draw conclusions between the differences of two population diets, yet it is still cited as a supporting evidence of turmeric's benefits.

In short, we all got conned. If we don't develop more awareness of the implications of bad science on our lives, taxpayer money will continue to be funneled into a black hole of falsely promising studies. So the next time you wonder whether you should buy a supplement, ask your scientist friend first. We’re here and eager to help.