Luteolin - Another fascinating compound in plants

Luteolin is a flavonoid – a compound in plants that gives yellow or red/blue pigments designed to attract pollinators. Flavonoids also fix nitrogen, regulate plant physiology and inhibit plant diseases. When we humans eat plants, the flavonoids therein may have many beneficial effects. Research on luteolin is an example.

Dr. Daniel Hwang is a molecular biologist at UC Davis. He has studied the ways in which luteolin (and other plant compounds – quercetin, eriodicytol, hesperidin, naringenin) apparently act as anti-inflammatory agents. These compounds target an enzyme in humans that can increase inflammation. Luteolin was found to be the most effective inhibitor of this enzyme. Since unchecked inflammation is associated with heart disease, cancer and problems of aging, this finding is a step on the way to prevention.

Researchers at the University of Illinois, led by Dr. Rodney Johnson, study anti-inflammatory compounds and their effects on the brain aging. They have found that luteolin can reduce inflammation in the brain as well as in other parts of the body. When infection occurs anywhere in the body, brain cells called microglia produce inflammatory chemical messengers that help to fight off the infection. This process is beneficial if it is limited to the acute infection. The inflammatory response is associated with sleepiness, loss of appetite, fever and lethargy, and sometimes a temporary diminishment of memory and learning. Some neurons may self-destruct in this process. Inflammation in the central nervous system can be serious if it goes on too long. Luteolin was found to diminish this inflammatory response, by shutting down a key component in the inflammatory pathway.
When aged mice were fed a diet supplemented with luteolin, they did better on tests of learning and memory tasks than the aged mice controls; the levels of inflammatory markers in their brains were similar to younger adult mice. The researchers concluded that natural compounds in fruits and vegetables, by being anti-inflammatory, could inhibit cognitive aging. Johnson thinks that his team’s results are applicable to other conditions with an inflammatory component, including diabetes and obesity.

Just published research by Professor Jung Park in Korea has shown that luteolin inhibits cell signaling pathways important for the growth of colon cancer cells. Blocking these pathways can stop colon cancer cells from dividing, and can lead to cancer cell death.

Dietary sources of luteolin include celery, green pepper, thyme, chamomile, carrots, olive oil, peppermint, rosemary and oregano. Luteolin is also being sold as a supplement, and should not be taken as such. You may remember the study showing that smokers taking beta-carotene supplements developed more lung cancer and had higher death rates than those without such a supplement. It was felt that taking an excess of one carotene may have inhibited the absorption of other carotenes from food. There are many flavonoids in plant foods, and they may act synergistically with each other. Taking any one of these as a supplement is unwise and untested. Earlier in this article I wrote about quercetin – found in apples, capers and onions, and eriodicytol, hesperidin, and naringenin - found in citrus fruits. The take home lesson from research on flavonoids is – keep eating a wide variety of vegetables and fruits. Remember what Michael Pollan said: Eat food, not too much, mostly plants.
Sadja Greenwood, MD,MPH back issues on this blog