Dark green, deep orange, and bright red fruits and vegetables can deliver more than 600 different carotenoids. About 50 of these have provitamin A activity. The most relevant provitamin A carotenoids for humans are α-carotene, β-carotene, and β-cryptoxanthin, of which β-carotene provides the majority of vitamin A to Africans and Asians. Several factors influence the bioavailability of carotenoids from food, thereby decreasing overall bioefficacy[7-11]. Fully formed vitamin A comes only from liver, fish-liver oils, margarine, butter, milk, and eggs, and while small portions of those foods deliver needed nutrients, overdoing them can be a health hazard.
One of vitamin A's top jobs is to take care of our body's surfaces, inside and out, which are lined with epithelial cells that protect our body against germ warfare. Outside, vitamin A makes epithelial cells tough, to create skin. Inside, it makes them tender, to create mucous membranes that line the nose, mouth, lungs, stomach, intestines, bladder, urethra, uterus, and vagina, forming a barrier against invading germs.
Vitamin A also creates the mucus itself. This sticky fluid is essential because it prevents our stomach lining from being digested along with our food, and in our lungs, it traps debris and hauls it out of airways before it can hurt our body.
Vitamin A is also vital for maintaining vision, forming bones, and building healthy babies. Plus, researchers suspect that it beefs up sensors that notice cancer cells and warn our immune system to take action.
Beta-carotene and its clan have amazing synergy. Each family member attacks cancer in a different way, creating far more cancer-killing power than any one of them working alone. For instance, beta-carotene gobbles up free radicals from fluids located inside and ouside the body's fats. Lycopene may arrest the growth of tumor cells. Still other carotenoids may stimulate an enzyme in our immune system that breaks down carcinogens. Note that alpha-carotene is even more effective at stopping cancer cells than beta-carotene. Because dark green and orange-colored vegetables are the richest sources of alpha-carotene, scientists can access our vegetable consumption with a blood test for alpha-carotene, not beta-carotene which is present in most multivitamins and supplements.
Beta-carotene alone can supercharge our immune system. It's been shown to jump-start natural killer cell activity in older men. It makes bacteria-munching monocytes work more effectively, and it highlights troublemaking antigens so that helper T cells can make the right antibodies to neutralize the antigens.
"A diet rich in beta-carotene from plenty of fruits and vegetables may reduce the risk of breast cancer recurrence by one-third," says Cheryl Rock, R.D., Ph.D., associate professor of family and preventive medicine at the University of California, San Diego.
One recent study of nonsmokers gave the nod to vegetables-tomatoes, lettuce, and carrots-and suggested that eating more of these and other vegetables may lower lung cancer risk by 25% for nonsmokers. Also, 16 years into the Nurses' Health Study, researchers have learned that eating more vegetables, especially carrots, may significantly lower lung cancer risk, even in women who smoke.
Another study, in Italy, found that among people who had never smoked, eating more fruits and carrots, along with reducing alcohol and saturated fat intake, may cut the risk of cancers of the mouth and pharynx.
The risk of developing pancreatic cancer is related in part to the amount of sugar in the diet. Some researches show that:
Beta-carotene and company don't just fight cancer. They also stave off heart disease. Beta-carotene and lycopene fight a process that makes "bad" low-density lipoprotein (LDL) cholesterol even more likely to contribute to plaque formation on artery walls. A study of more than 85,000 nurses showed that a diet rich in beta-carotene reduced the risk of heart disease by 22%.
Good for Vision
A study in Nepal showed that high beta-carotene intake reduced night blindness among pregnant women by 50%.
Recent research suggests that Lutein, another carotenoids family member, may protect our eye tissues from damage that leads to age-related macular degeneration, the leading cause of blindness in older Americans. Lutein pumps up the macula of our eye (critical for reading, watching the speedometer, and noticing stop signs), protecting it against harmful blue light and thus fending off age-related macular degeneration.
Beta-carotene may help protect our skin against sunburn. In one study, women who got lots of beta-carotene and used sun-screen got more sunburn protection than those who used sun-screen alone.
When it comes to arthritis, the carotene called beta cryptoxanthin may reduce the risk of developing inflammation-related disorders, including RA. Researchers from the United Kindom found that people who ate diets high in beta cryptoxanthin were half as likely to develop a form of inflammatory arthritis as those who ate very few beta cryptoxanthin foods. They found that adding just one additional serving each day of a food high in beta cryptoxanthin helped reduce arthritis risk.
Other studies showed that diets enriched with antioxidant nutrients, including selenium, beta-carotene, vitamin E, and vitamin C, inhibit the formation of UV-induced tumors. Findings suggest that UV damage to the epidermis affects deeper layers of the skin and even blood and other tissues.
Supplement Is Not the Same
A Finnish study found that lung cancer actually increased among 29,000 smokers taking high-dose beta-carotene supplements. And, in a study of 22,000 male American doctors, researchers found that scarfing down 50 mgs supplements every other day had absolutely no effect, good or bad, on the men's risk of cancer, heart, disease, or death from any cause. The lesson here is that you should focus on plant foods instead of pills.
Kidney stone formers who restrict green leafy and yellow-orange vegetables due to their high oxalate content may benefit from beta-carotene supplements. However, megadoses of vitamin A itself can lead to increased calcium excretion and liver toxicity. For example, anything over 5000 IU of vitamin A (not beta-carotene) is considered too much for someone with Hepatitis C to take in one day and may be toxic.
We prefer natural carotenoids (such as beta-carotene) which the liver converts into vitamin A as needed. Orange, yellow, and red fruits and vegetables, such as:
are packed with carotenoids, so it's easy to get all you need from them. They're also loaded with fiber, fluids, and other newly discovered (and possibly undiscovered) phytochemicals that work together for better health.