Bright colors in fruits and vegetables generally indicate high levels of nutrients and other healthful compounds, including the pigments themselves (such as beta carotene in carrots). Strong, sharp flavors of plant-derived foods and spices are also usually a sign of potentially beneficial substances. So it’s not surprising that traditional medicine, especially in India and China, has used spices to treat a variety of ailments.
One colorful spice that has been the focus of extensive study in recent years is turmeric, made from the ground, dried roots of the Curcuma longa plant, native to India. The main component of curry powder, turmeric imparts a distinct earthy flavor (slightly peppery and mustardy) and vibrant yellow-to-orange hue to food.
Scientists have identified more than 300 compounds in turmeric, but the one that has gotten the most attention is curcumin, which is a polyphenol. (Don’t confuse curcumin with cumin, which is a different spice that is also found in curry powder.)
Laboratory and animal research shows that, like many substances in plants, curcumin has an array of potentially beneficial properties, including anti-inflammatory, antioxidant, antibacterial, neuroprotective, immunity-modulating, and anti-cancer activity. Other compounds in turmeric, notably various curcuminoids (relatives of curcumin), have some of these properties as well.
Many human clinical trials on curcumin have been done or are underway, focusing on its potential roles in treating or preventing just about everything—from inflammatory conditions (such as arthritis and colitis), cancer, cardiovascular disease, and dementia to depression, diabetes, indigestion, post-exercise muscle soreness, obesity, skin diseases, and ulcers.
Because of the proposed benefits and a lot of marketing promotion (including pitches by Dr. Oz), curcumin and turmeric have become best-selling supplements, usually in capsule form. Marketers of the supplements have moved aggressively forward, often making claims that are far ahead of the research. For example, the headline of a recent press release quoted one marketer as saying that turmeric is “one of nature’s greatest gifts to mankind.”
A sprinkling of curcumin research
Below is a sampling of findings about curcumin from some of the better human studies. Keep in mind that most studies have been small and short, and many have not compared curcumin to a placebo. And the studies have often had inconsistent results. Thus, positive findings should be considered preliminary at best, needing replication in larger, better trials. Most studies have used curcumin capsules (one to three times a day), though some used capsules also containing other curcuminoids. Turmeric capsules may contain the spice itself, a concentrated extract, or both, so the concentration of curcuminoids can vary greatly. Many studies were funded by the manufacturers of the supplements used in them.
Another major caveat is that curcumin is poorly absorbed, and the little that is absorbed is rapidly broken down and eliminated from the body. That greatly reduces the likelihood that it will have biological effects and therapeutic efficacy. Scientists are attempting to develop forms of curcumin that are better absorbed or add substances that facilitate absorption (such as piperine, from black pepper), but more clinical research is needed.
- Diabetes. A clinical trial from Thailand, published in Diabetes Care in 2012, found that people with prediabetes who took curcumin for nine months had improved function of insulin-producing cells in the pancreas, along with a significantly reduced risk of developing type 2 diabetes. Other studies suggest that curcumin can improve insulin sensitivity.
- Cardiovascular disease. In a small Japanese study in Nutrition Research in 2012, postmenopausal women who took curcumin for eight weeks had an improvement in arterial function, comparable to that seen in women who engaged in aerobic exercise. Studies looking at curcumin’s effects on cholesterol and other lipids have had inconsistent results. An Iranian study in Phytotherapy Research in 2013 found that curcumin did not improve cholesterol levels but did reduce triglycerides, while a Taiwanese study in the same journal in 2014 found that curcumin significantly reduced LDL (“bad”) cholesterol and triglycerides in people with metabolic syndrome.
- Arthritis. A few studies have found that curcumin can reduce pain from rheumatoid arthritis or osteoarthritis, sometimes as much as anti-inflammatory drugs. A small Iranian clinical trial in Phytotherapy Research in 2014 found that curcuminoids, combined with an extract of black pepper and taken for six weeks, improved symptoms of knee osteoarthritis, compared to a placebo.
- Cognition. Despite some promising lab research on brain cells, the few studies in humans have mostly found little or no benefit. This year a well-designed Australian study in the British Journal of Nutrition found that a curcumin supplement had no cognitive benefits in older people who took it for a year, compared to a placebo group. In contrast, another Australian study, in the Journal of Psychopharmacology in 2015, found that curcumin improved attention and working memory and reduced mental fatigue in older people who took it for four weeks, compared to a placebo. As for people with Alzheimer’s disease, studies “have not been able to generate the anticipated benefits of curcumin,” according to a review in the British Journal of Nutrition in 2016.
- Ulcerative colitis. Several small clinical trials suggest that curcumin can help people with this inflammatory bowel disease. The most recent study, in Clinical Gastroenterology and Hepatology in 2015, found that in people with mild to moderate ulcerative colitis who took standard medication (mesalamine), the addition of a high-dose curcumin supplement helped half of them achieve remission after four weeks; none of those given a placebo benefited. The researchers called for larger clinical trials to confirm their findings.
Spices add variety and complexity to our diets. Besides small amounts of vitamins and minerals, they contain other potentially healthful compounds.
How safe are curcumin and turmeric?
Curcumin has generally been found to be safe even at high doses, at least with short-term use. Still, there have been reports of diarrhea, abdominal pain or discomfort, rashes, headaches, yellow stool, and nausea from high doses. Long-term safety of high doses is unknown. The spice turmeric, like certain dark leafy greens, contains a high concentration of oxalates, which can reduce absorption of iron and other minerals; curcumin extracts would not contain oxalates. People who form calcium oxalate kidney stones (the most common type) need to limit their intake of dietary oxalates and thus should avoid high amounts of turmeric, some research suggests.
Too good to be true?
Researchers from the MD Anderson Cancer Center at the University of Texas looked at the clinical trials on curcumin in a 2013 review in the AAPS Journal. They concluded that “from the findings of the completed clinical trials, it may seem that curcumin’s clinical efficacy is too good to be true ... However, poor bioavailability and limited adverse effects reported by some investigators are a major limitation to the therapeutic utility of curcumin.”
Bottom line: It’s good that scientists continue to study spices and other plant compounds. Some of these may turn out to be like aspirin, which was isolated from willow bark more than a century ago. Maybe one day, curcumin, with or without other compounds from turmeric, will yield such a drug that can be purified and standardized.
For now, the research on curcumin, while promising, is still preliminary. We don’t recommend the supplements because of the many unknowns—about absorbability, proper dosing, and safety. The supplements contain varying components of turmeric in widely ranging doses. Be skeptical of marketing claims that certain brands have “enhanced bioavailability”—only well-designed trials can determine if this is true and whether this yields clinical benefits.
We recommend getting curcumin from turmeric, if you like its taste, even though this is a less concentrated source than most supplements. Consuming turmeric with food containing fat may boost the absorption of its curcumin.