You may know beta-carotene as the little pill that couldn’t. Beta-carotene supplements were flying off the shelves, until studies in 1994 and 1996 found no benefit, and two even suggested they could harm smokers.
But beta-carotene is just one of 600 colorful pigments that belong to a family of natural plant chemicals called “carotenoids.” Carotenoids give fruits and vegetables their yellow, orange and red colors. They’re also abundant in dark green vegetables, where their tell-tale colors are masked by even more abundant chlorophyll.
The most common carotenoids in blood and tissues are alpha-carotene, beta-carotene, beta-cryptoxanthin, lycopene, lutein and zeaxanthin.
Despite their family connection, not all carotenoids are alike. Of the major ones, only alpha-carotene, beta-carotene and beta-cryptoxanthin can be converted to vitamin A in the body. Many carotenoids, however, act as antioxidants, protecting cells by disabling compounds called “free radicals” before they can cause damage or disease.
Researchers are just beginning to learn how specific carotenoids can influence our health by boosting immune response, protecting the heart and eyes from chronic disease, and decreasing the risk of some cancers. Here, we look at the latest discoveries.
The Carotene Quandary. To alpha or beta? For years, beta-carotene was the darling of the carotenoids. Researchers simply assumed it was responsible for the health-protecting effects of fruits and vegetables, because it generates the most vitamin A conversion. After studies showed that the incidence of lung cancer increased in smokers who took beta-carotene supplements, researchers from the National Cancer Institute found that beta-carotene—even in foods—was not the main protector against lung cancer. Alphacarotene lowered risk more.
The upshot? It makes sense to eat a variety of vegetables and fruits to get a mix of carotenoids. (And, certainly, to not smoke.)
Lycopene’s Link to Cancer. Lycopene (found mostly in tomatoes) is the predominant carotenoid in the blood and prostate gland. It cannot be converted to vitamin A, but it has twice the antioxidant potency of its betacarotene cousin. In recent laboratory and animal studies, lycopene suppressed cancer cell growth. Other studies have linked diets rich in lycopene to reduced risk of prostate and digestive tract cancers.
One U.S. study linked intake of tomato sauce, tomatoes and pizza to lowered risk of prostate cancer. Tomato juice, however, was not protective. That’s not surprising. According to John Erdman, Ph.D., of the University of Illinois in Urbana, lycopene is a fat-soluble substance, so it needs some fat, like that found in pizza and most pasta sauces, to be absorbed. The lycopene in tomato juice, however, seems to be especially poorly absorbed. Also, cooked tomato products are a better source of lycopene than raw tomatoes, because heat ruptures plant cell walls, releasing the carotenoid.
Still, an Italian study of 2,700 adults found that people who ate seven or more servings of raw tomatoes a week had about a 60% lower risk of stomach, colon and rectal cancers than those who ate two or fewer servings a week. It’s unclear, though, if the reduced risk was due to the lycopene in the tomatoes or simply to a healthful Mediterranean diet rich in other fruits and vegetables, as well as tomatoes.
The Eyes Have It. Lutein and its close relative zeaxanthin are the main carotenoids found in the macula, the central portion of the retina that allows you to see details clearly. It’s believed these antioxidants help protect the retina from free radicals.
Oxidative damage from free radicals causes the macula to break down, or degenerate, triggering vision loss. This “age-related macular degeneration,” or AMD, affects about 10 million Americans and is the leading cause of irreversible blindness in adults over 65.
In a Harvard University study, those who had the highest intake of carotenoids, especially from dark leafy greens, had 43% less risk of advanced AMD than those with the lowest intake. And the more high-lutein/zeaxanthin foods eaten, the better. Researchers still don’t know for sure it isn’t something else in these foods that’s responsible for the effect. But either way, it’s one more reason to load up on those dark leafy greens.
Counting Your Carotenoids. How much is enough? No one is sure. At the moment, there is no official recommended intake of carotenoids, though a National Academy of Sciences panel of experts will soon convene to discuss making recommendations for antioxidants, including carotenoids.
Current estimates for optimum intake still focus on beta-caotene and run the gamut from 6 to 30 milligrams a day. Rather than focus on milligrams, however, just aim for more than five servings a day of fruits and vegetables that are mostly yellow-orange, red or dark green. (See chart.)
What about new heavily marketed supplements that contain lycopene? Or “tomato oil” from tomatoes cross-bred to be super-rich in lycopene? Or lutein supplements “for healthy eyes”? EN does not endorse them. Carotenoids interact with each other, and supplemental doses of one carotenoid may impair the absorption of others.
Moreover, taking supplements instead of improving your diet may mean missing out on other health-promoting substances in foods. Besides, it’s quite possible the myriad of substances in fruits and vegetables—vitamins, minerals, fiber and a host of phytochemicals—are most protective when they are packaged together, as in foods.
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