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What does it do? Beta-carotene is a substance from plants that the body converts into vitamin A. It also acts as an antioxidant and an immune system booster. Other members of the antioxidant carotenoid family include cryptoxanthin, alpha-carotene, zeaxanthin, lutein, and lycopene. However, unlike beta-carotene, most of these nutrients are not converted to vitamin A in significant amounts.
Where is it found? Dark green and orange-yellow vegetables are good sources of beta-carotene. It is also available in supplements.
Who is likely to be deficient? People who limit their consumption of beta-carotene-containing vegetables could be at higher risk of developing a vitamin A deficiency. However, because beta-carotene is not an essential nutrient, true deficiencies do not occur. Nevertheless, very old persons with type 2 diabetes have shown a significant age-related decline in blood levels of carotenoids, irrespective of their dietary intake.1
Which form is best? Most beta-carotene in supplements is synthetic, consisting of only one molecule called all trans beta-carotene. Natural beta-carotene, found in food, is made of two molecules—all trans beta-carotene and 9-cis beta-carotene.
Researchers originally saw no meaningful difference between natural and synthetic beta-carotene. This view was questioned when the link between beta-carotene-containing foods (all natural) and lung cancer prevention2 was not duplicated in studies using synthetic pills.3 In smokers, synthetic beta-carotene has apparently caused an increased risk of lung cancer4 5 6 and disease of the blood vessels7 in double-blind research. Animal research has begun to identify the ways in which synthetic beta-carotene might cause damage to lungs, particularly when animals are exposed to cigarette smoke.8
Much of natural beta-carotene is in the all trans molecule form—the same as synthetic beta-carotene. Moreover, much of the 9-cis molecule found only in natural beta-carotene is converted to the synthetic molecule before it reaches the bloodstream.9 Also, absorption of 9-cis beta-carotene appears to be poor,10 though some researchers question this finding.11
Despite the overlap between natural and synthetic forms, natural beta-carotene may possibly have activity that is distinct from the synthetic form. For example, studies in both animals12 and humans13 have shown that the natural form has antioxidant activity that the synthetic form lacks. Also, in one trial, pre-cancerous changes in people reverted to normal tissue with natural beta-carotene supplements, but not with synthetic supplements.14 Israeli researchers have investigated whether the special antioxidant effects of natural beta-carotene might help people suffering from asthma attacks triggered by exercise.15 People with asthma triggered by exercise were given 64 mg per day of natural beta-carotene for one week. In that report, 20 of 38 patients receiving natural beta-carotene were protected against exercise-induced asthma. However, because synthetic beta-carotene was not tested, the difference between the activity of the two supplements cannot be deduced from this report.
Increasingly, doctors are recommending that people supplement only with natural beta-carotene. However, no studies have explored whether the adverse effect of synthetic beta-carotene in cigarette smokers would also occur with natural beta-carotene supplementation. Until more is known, smokers should avoid all beta-carotene supplements and others should avoid synthetic beta-carotene.
In supplements, the natural form can be identified by the phrases "from D. salina," "from an algal source," "from a palm source," or as "natural beta-carotene" on the label. The synthetic form is identified as "beta-carotene."
How much is usually taken? The most common beta-carotene supplement intake is probably 25,000 IU (15 mg) per day, though some people take as much as 100,000 IU (60 mg) per day. Whether the average person would benefit from supplementation with beta-carotene remains unclear.
Are there any side effects or interactions? Beta-carotene supplementation, even in very large amounts, is not known to cause any serious side effects,16 17 however, excessive intake (more than 100,000 IU, or 60 mg per day) sometimes gives the skin a yellow-orange hue. People taking beta-carotene for long periods of time should also supplement with vitamin E, as beta-carotene may reduce vitamin E levels.18 Beta carotene supplementation may also decrease blood levels of lutein, another carotenoid.19
As noted above, synthetic beta-carotene has now been linked to increased risk of lung cancer in smokers. Pre-cancerous changes to lungs have appeared in animals given synthetic beta-carotene supplements, particularly those exposed to tobacco smoke. Though some research suggests that differences between synthetic and natural supplements may exist, conclusive proof of such a difference has not yet been shown.
Preliminary studies in animals indicate that beta-carotene supplementation, when combined with heavy alcohol consumption, may enhance liver toxicity.20 Until more is known, alcoholics and persons who consume alcohol on a daily basis should avoid supplementing with beta-carotene.
One study showed a slightly increased risk of vascular surgery among people with intermittent claudication who took beta-carotene supplements.21 Until more is known, persons wishing to use beta-carotene supplements should first consult with their doctor.
Where is it found? Dark green and orange-yellow vegetables are good sources of beta-carotene. It is also available in supplements.
Who is likely to be deficient? People who limit their consumption of beta-carotene-containing vegetables could be at higher risk of developing a vitamin A deficiency. However, because beta-carotene is not an essential nutrient, true deficiencies do not occur. Nevertheless, very old persons with type 2 diabetes have shown a significant age-related decline in blood levels of carotenoids, irrespective of their dietary intake.1
Which form is best? Most beta-carotene in supplements is synthetic, consisting of only one molecule called all trans beta-carotene. Natural beta-carotene, found in food, is made of two molecules—all trans beta-carotene and 9-cis beta-carotene.
Researchers originally saw no meaningful difference between natural and synthetic beta-carotene. This view was questioned when the link between beta-carotene-containing foods (all natural) and lung cancer prevention2 was not duplicated in studies using synthetic pills.3 In smokers, synthetic beta-carotene has apparently caused an increased risk of lung cancer4 5 6 and disease of the blood vessels7 in double-blind research. Animal research has begun to identify the ways in which synthetic beta-carotene might cause damage to lungs, particularly when animals are exposed to cigarette smoke.8
Much of natural beta-carotene is in the all trans molecule form—the same as synthetic beta-carotene. Moreover, much of the 9-cis molecule found only in natural beta-carotene is converted to the synthetic molecule before it reaches the bloodstream.9 Also, absorption of 9-cis beta-carotene appears to be poor,10 though some researchers question this finding.11
Despite the overlap between natural and synthetic forms, natural beta-carotene may possibly have activity that is distinct from the synthetic form. For example, studies in both animals12 and humans13 have shown that the natural form has antioxidant activity that the synthetic form lacks. Also, in one trial, pre-cancerous changes in people reverted to normal tissue with natural beta-carotene supplements, but not with synthetic supplements.14 Israeli researchers have investigated whether the special antioxidant effects of natural beta-carotene might help people suffering from asthma attacks triggered by exercise.15 People with asthma triggered by exercise were given 64 mg per day of natural beta-carotene for one week. In that report, 20 of 38 patients receiving natural beta-carotene were protected against exercise-induced asthma. However, because synthetic beta-carotene was not tested, the difference between the activity of the two supplements cannot be deduced from this report.
Increasingly, doctors are recommending that people supplement only with natural beta-carotene. However, no studies have explored whether the adverse effect of synthetic beta-carotene in cigarette smokers would also occur with natural beta-carotene supplementation. Until more is known, smokers should avoid all beta-carotene supplements and others should avoid synthetic beta-carotene.
In supplements, the natural form can be identified by the phrases "from D. salina," "from an algal source," "from a palm source," or as "natural beta-carotene" on the label. The synthetic form is identified as "beta-carotene."
How much is usually taken? The most common beta-carotene supplement intake is probably 25,000 IU (15 mg) per day, though some people take as much as 100,000 IU (60 mg) per day. Whether the average person would benefit from supplementation with beta-carotene remains unclear.
Are there any side effects or interactions? Beta-carotene supplementation, even in very large amounts, is not known to cause any serious side effects,16 17 however, excessive intake (more than 100,000 IU, or 60 mg per day) sometimes gives the skin a yellow-orange hue. People taking beta-carotene for long periods of time should also supplement with vitamin E, as beta-carotene may reduce vitamin E levels.18 Beta carotene supplementation may also decrease blood levels of lutein, another carotenoid.19
As noted above, synthetic beta-carotene has now been linked to increased risk of lung cancer in smokers. Pre-cancerous changes to lungs have appeared in animals given synthetic beta-carotene supplements, particularly those exposed to tobacco smoke. Though some research suggests that differences between synthetic and natural supplements may exist, conclusive proof of such a difference has not yet been shown.
Preliminary studies in animals indicate that beta-carotene supplementation, when combined with heavy alcohol consumption, may enhance liver toxicity.20 Until more is known, alcoholics and persons who consume alcohol on a daily basis should avoid supplementing with beta-carotene.
One study showed a slightly increased risk of vascular surgery among people with intermittent claudication who took beta-carotene supplements.21 Until more is known, persons wishing to use beta-carotene supplements should first consult with their doctor.