Reliable
and relatively consistent scientific data showing a substantial health benefit. Contradictory, insufficient, or preliminary studies
suggesting a health benefit or minimal health benefit. For an herb, supported by traditional use but minimal
or no scientific evidence. For a supplement, little scientific support and/or minimal health
benefit.
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
cancer456 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,1617 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
Warning: Synthetic beta-carotene has now been linked to increased
risk of lung cancer in smokers. Until more is
known, smokers should avoid all beta-carotene supplements.
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.
Are there any drug
interactions?
Certain medicines may interact with beta-carotene. Refer to drug interactions for a list of those medicines.
References (To view, roll mouse over the "References" heading; to hide, click on the heading)
1. Polidori MC, Mecocci P, Stahl W, et al. Plasma levels of lipophilic
antioxidants in very old patients with type 2 diabetes. Diabetes Metab Res Rev
2000;16:15–9.
2. Shekelle RB, Lepper M, Liu S, et al. Dietary vitamin A and risk of
cancer in the Western Electric Study. Lancet 1981;2:1185–90.
3. Hennekens CH, Burning JE, Manson JE, et al. Lack of effect of
long-term supplementation with beta carotene on the incidence of malignant neoplasms and
cardiovascular disease. N Engl J Med 1996;334:1145–9.
4. Albanes D, Heinone OP, Taylor PR, et al. Alpha-tocopherol and
beta-carotene supplements and lung cancer incidence in the Alpha-Tocopherol, Beta-Carotene
Cancer Prevention Study: effects of base-line characteristics and study compliance. J Natl
Cancer Inst 1996;88:1560–70.
5. Omenn GS, Goodman GE, Thornquist MD, et al. Effects of a combination
of beta carotene and vitamin A on lung cancer and cardiovascular disease. N Engl J
Med 1996;334:1150–5.
6. Lee IM, Cook NR, Manson JE, et al. Beta-carotene supplementation and
incidence of cancer and cardiovascular disease: the Women’s Health Study. J Natl
Cancer Inst 1999;91:2102–6.
7. Törnwall ME, Virtamo J, Haukka JK, et al. The effect of
alpha-tocopherol and beta-carotene supplementation on symptoms and progression of intermittent
claudication in a controlled trial. Atherosclerosis 1999;147:193–7.
8. Wang XD, Liu C, Bronson RT, et al. Retinoid signaling and activator
protein-1 expression in ferrets given ß-carotene supplements and exposed to tobacco
smoke. J Natl Cancer Inst 1999;91:60–6.
9. You CS, Parker RS, Goodman KJ, et al. Evidence of cis-trans
isomerization of 9-cis-beta-carotene during absorption in humans. Am J Clin Nutr
1996;64:177–83.
10. Tamai H, Morinobu T, Murata T, et al. 9-cis beta-carotene in human
plasma and blood cells after ingestion of beta-carotene. Lipids
1995;30:493–8.
11. Ben-Amotz A, Levy Y. Bioavailability of a natural isomer mixture
compared with synthetic all-trans beta-carotene in human serum. Am J Clin Nutr
1996;63:729–34.
12. Bitterman N, Melamed Y, Ben-Amotz A. Beta-carotene and CNS oxygen
toxicity in rats. J Appl Physiol 1994;76:1073–6.
13. Ben-Amotz A, Levy Y. Bioavailability of a natural isomer mixture
compared with synthetic all-trans beta-carotene in human serum. Am J Clin Nutr
1996;63:729–34.
14. Yeum KJ, Azhu S, Xiao S, et al. Beta-carotene intervention trial in
premalignant gastric lesions. J Am Coll Nutr 1995;14:536 [abstr #48].
15. Neuman I, Nahum H, Ben-Amotz A. Prevention of exercise-induced asthma
by a natural isomer mixture of beta-carotene. Ann Allergy Asthma Immunol
1999;82:549–53.
16. Olson JA. Recommended dietary intakes (RDI) of vitamin A in humans.
Am J Clin Nutr 1987;45:704–16.
17. Heywood R, Palmer AK, Gregson RL, Hummler H. The toxicity of
beta-carotene. Toxicology 1985;36:91–100.
18. Xu MJ, Plezia PM, Alberts DS, et al. Reduction in plasma or skin
alpha-tocopherol concentration with long-term oral administration of beta-carotene in humans
and mice. J Natl Cancer Inst 1992;84:1559–65.
19. Gossage C, Deyhim M, Moser-Veillon PB, et al. Effect of beta-carotene
supplementation and lactation on carotenoid metabolism and mitogenic T lymphocyte
proliferation. Am J Clin Nutr 2000;71:950–5.
20. Leo MA, Lieber CS. Alcohol, vitamin A, and beta-carotene: adverse
interactions, including hepatotoxicity and carcinogenicity. Am J Clin Nutr
1999;69:1071–85 [review].
21. Törnwall ME, Virtamo J, Haukka JK, et al. The effect of
alpha-tocopherol and beta-carotene supplementation on symptoms and progression of intermittent
claudication in a controlled trial. Atherosclerosis 1999;147:193–7.
The information presented in Aisle7 is for informational purposes only.
It is based on scientific studies (human, animal, or in vitro), clinical experience,
or traditional usage as cited in each article. The results reported may not necessarily occur
in all individuals. For many of the conditions discussed, treatment with prescription or over
the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist
for any health problem and before using any supplements or before making any changes in
prescribed medications.
