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Whether people who already consume a diet high in fruits and vegetables would benefit further from supplementation with a mixture of carotenoids remains unknown. While smokers clearly should not supplement with isolated synthetic Reference beta-carotene, the effect in smokers of taking either natural beta-carotene or mixed carotenoids is not clear.

Nonetheless, based on health-promoting effects associated with these levels in preliminary research, some doctors recommend that most people supplement with up to 25,000 IU (15 mg) per day of natural beta-carotene and approximately 6 mg each of alpha-carotene, Reference lutein, and Reference lycopene.

Carotenoids are found in all plant foods. In general, the greater the intensity of color, the higher the level of carotenoids. In green leafy vegetables, Reference beta-carotene is the predominant carotenoid. In the orange colored fruits and vegetables—such as carrots, apricots, mangoes, yams, winter squash—beta-carotene concentrations are high, but other pro-vitamin A carotenoids typically predominate. Yellow vegetables have higher concentrations of yellow carotenoids (xanthophylls), hence a lowered pro-vitamin A activity; but some of these compounds, such as Reference lutein, may have significant health benefits, potentially due to their Reference antioxidant effects. The red and purple vegetables and fruits—such as tomatoes, red cabbage, berries, and plums—contain a large portion of non-vitamin A–active carotenoids. Legumes, grains, and seeds are also significant sources of carotenoids. Carotenoids are also found in various animal foods, such as salmon, egg yolks, shellfish, milk, and poultry. A variety of carotenoids is also found in carrot juice and “green drinks” made from vegetables, dehydrated barley greens, or wheat grass.

Synthetic beta-carotene is available as a supplement. Mixed carotenoids (including the natural form of beta-carotene) are also available in supplements derived from palm oil, algae, and carrot oil.

Carotenoid deficiency is not considered a classic nutritional deficiency like scurvy or beri-beri (severe Reference vitamin C and Reference vitamin B1 deficiencies, respectively). However, given the possible health benefits of carotenoids, most doctors recommend adequate intake. People who do not frequently consume carotenoid-rich foods or take carotenoid supplements are likely to be taking in less than adequate amounts, though optimal levels remain unknown. Also, deficiency may be found in people with chronic Reference diarrhea or other disorders associated with impaired absorption.

Carotenoids are generally regarded as safe, based primarily on studies with Reference beta-carotene. Increased consumption of carotenoids may cause to the skin to turn orange or yellow—a condition known as “carotenodermia.” This occurrence is completely benign and is unrelated to jaundice—the yellowing of the skin that can result from liver disease or other causes.

Until more is known, people especially smokers should not supplement with synthetic beta-carotene. Two double-blind studies have shown that supplementation with isolated synthetic beta-carotene may increase the risk of Reference lung cancer in people who smoke.^{7 , 8} Moreover, three of four studies have found small increases in the risk of Reference heart disease in people assigned to take synthetic beta-carotene compared with those assigned to take placebo.^{9 , 10 , 11 , 12}