What Are "Star" Ratings?
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.
Our proprietary “Star-Rating” system was developed to help you easily understand the amount of scientific support behind each supplement in relation to a specific health condition. While there is no way to predict whether a vitamin, mineral, or herb will successfully treat or prevent associated health conditions, our unique ratings tell you how well these supplements are understood by the medical community, and whether studies have found them to be effective for other people.
For over a decade, our team has combed through thousands of research articles published in reputable journals. To help you make educated decisions, and to better understand controversial or confusing supplements, our medical experts have digested the science into these three easy-to-follow ratings. We hope this provides you with a helpful resource to make informed decisions towards your health and well-being.
This supplement has been used in connection with the following health conditions:
|150,000 IU twice per week||Beta-carotene, the most widely used supplement in the treatment of leukoplakia, has been shown in studies to increase remission rate.|
150,000 IU twice per week
Caution: Synthetic beta-carotene has been linked to increased risk of lung cancer in smokers. Until more is known, smokers should avoid all beta-carotene supplements.
Beta-carotene is the most widely used supplement in the treatment of leukoplakia. In a clinical trial of betel nut chewers with leukoplakia, supplementation with 150,000 IU of beta-carotene twice per week for six months significantly increased the remission rate compared with placebo (14.8% vs. 3.0%).1 The effectiveness of beta-carotene for treating leukoplakia was also confirmed in a double-blind trial that used 100,000 IU per day for six months.2 In one trial, supplementation with 33, 333 IU of beta-carotene per day, alone or combined with 50 IU of vitamin E, was reported not to reduce the incidence of leukoplakia.3 These results have also been observed in smaller trials.4 , 5
Drug therapy with a synthetic, prescription form of vitamin A (known as Accutane, isotretinoin, and 13-cis retinoic acid) has been reported to be more effective than treatment with 50,000 IU per day of beta-carotene.6 However, because of the potential toxicity of the vitamin A-like drug, it may be preferable to treat leukoplakia with beta-carotene, which is much safer.
Before the research on beta-carotene was published, vitamin A was used to treat leukoplakia.7 One group of researchers reported that vitamin A (28,500 IU per day) was more effective than beta-carotene in treating people with leukoplakia.8 Another trial found that the combination of 150,000 IU per week of beta-carotene plus 100,000 IU per week of vitamin A led to a significant increase in remission time compared to beta carotene alone in betel nut chewers.9 Women who are or who could become pregnant should not take 100,000 IU of vitamin A per week without medical supervision.
Lung Cancer in Nonsmokers
|Eat more carrots||Beta-carotene supplementation appears to reduce cancer risk in nonsmokers. Smokers should avoid beta-carotene supplements, including the amounts found in multivitamins.|
Lung Cancer in Nonsmokers
Eat more carrots
In double-blind trials, synthetic beta-carotene supplementation has led to an increased risk of lung cancer in smokers,10 , 11 though not in groups consisting primarily of nonsmokers.12 Smokers should avoid synthetic beta-carotene supplements, including the relatively small amounts found in many multivitamins.
The researchers who conducted the lung cancer trials have been criticized for not having used the natural form of beta-carotene.13 Preliminary evidence suggests that natural beta-carotene supplementation results in better antioxidant activity14 and anticancer activity in humans15 than does supplementation with synthetic beta-carotene. Nonetheless, much less is known about natural beta-carotene and questions remain about its potential efficacy.16 The effect of natural beta-carotene supplementation on lung cancer risk has yet to be studied.
The strong association between increased intake of beta-carotene from food and a reduced risk of lung cancer17 does not necessarily mean that supplementation with natural beta-carotene supplements would reduce the risk of lung cancer. Dietary beta-carotene may be a marker for diets high in certain fruits and vegetables that contain other anticancer substances that may be responsible for the protective effects. Until more is known, some doctors advise smokers to avoid all forms of beta-carotene supplementation—even natural beta-carotene.
|If deficient: 10,000 to 25,000 IU daily||Night blindness may be an early sign of vitamin A deficiency. Supplementing with beta-carotene, which the body converts into vitamin A, help correct such a deficiency and improve night blindness.|
If deficient: 10,000 to 25,000 IU daily
Caution: Synthetic beta-carotene has been linked to increased risk of lung cancer in smokers. Until more is known, smokers should avoid all beta-carotene supplements.
Night blindness may be an early sign of vitamin A deficiency. Such a deficiency may result from diets low in animal foods (the main source of vitamin A), such as eggs, dairy products, organ meats, and some fish. Low intake of fruits and vegetables containing beta-carotene, which the body converts into vitamin A, may also contribute to a vitamin A deficiency. Doctors often recommend 10,000 to 25,000 IU of vitamin A per day to correct a deficiency. Beta-carotene is less effective at correcting vitamin A deficiency than is vitamin A itself, because it is not absorbed as well and is only slowly converted by the body into vitamin A.
|100,000 to 300,000 IU daily under medical supervision||Beta-carotene is able to protect against free-radical damage caused by ultraviolet light and may help increase tolerance to sunlight.|
100,000 to 300,000 IU daily under medical supervision
Caution: Synthetic beta-carotene has been linked to increased risk of lung cancer in smokers. Until more is known, smokers should avoid all beta-carotene supplements.
Years ago, researchers theorized that beta-carotene in skin might help protect against sensitivity to ultraviolet light from the sun. Large amounts of beta-carotene (up to 300,000 IU per day for at least several months) have allowed people with photosensitivity to stay out in the sun several times longer than they otherwise could tolerate.18 , 19 , 20 The protective effect appears to result from beta-carotene’s ability to protect against free-radical damage caused by sunlight.21
|64 mg a day of natural supplement||Some researchers have suggested that exercise-related asthma attacks might be caused by free-radical damage caused by the exercise. Supplementing with beta-carotene, an antioxidant, protects against free-radical damage and may prevent these attacks.|
64 mg a day of natural supplement
Some researchers have suggested that asthma attacks triggered by exercise might be caused by free-radical damage caused by the exercise. Beta-carotene is an antioxidant that protects against free-radical damage. Israeli researchers reported that 64 mg per day of natural beta-carotene for one week in a double blind trial protected over half of a group of asthmatics who experienced attacks as a result of exercise.22 More research is needed to confirm this promising finding.
|25,000 to 100,000 IU per day for nonsmokers only||Beta-carotene has been shown to increase immune cell numbers and activity. It has also been shown to enhance cancer-fighting immune functions in healthy people.|
25,000 to 100,000 IU per day for nonsmokers only
Most,23 , 24 but not all,25 double-blind studies have shown that elderly people have better immune function and reduced infection rates when taking a multiple vitamin-mineral formula. In one double-blind trial, supplements of 100 mcg per day of selenium and 20 mg per day of zinc, with or without additional vitamin C, vitamin E, and beta-carotene, reduced infections in elderly people, though vitamins without minerals had no effect.26 Burn victims have also experienced fewer infections after receiving trace mineral supplements in double-blind research.27 These studies suggest that trace minerals may be the most important micronutrients for enhancing immunity and preventing infections in the elderly.
Beta-carotene and other carotenoids have increased immune cell numbers and activity in animal and human research, an effect that appears to be separate from their role as precursors to vitamin A.28 , 29 Placebo-controlled research has shown positive benefits of beta-carotene supplements in increasing numbers of some white blood cells and enhancing cancer-fighting immune functions in healthy people at 25,000–100,000 IU per day.30 , 31
In double-blind trials in the elderly, supplementation with 40,000–150,000 IU per day of beta-carotene has increased natural killer (NK) cell activity,32 but not several other measures of immunity.33
Controlled research has found that 50,000 IU per day of beta-carotene boosted immunity in people with colon cancer but in not those with precancerous conditions in the colon.34 Beta-carotene has also prevented immune suppression from ultraviolet light exposure.35 Effects on immunodefiency in HIV-positive people have been inconsistent using beta-carotene.36 , 37
|9,000 IU daily||Taking antioxidant supplements, such as beta-carotene, may lessen pain and prevent recurrences of pancreatitis.|
9,000 IU daily
Free radical damage has been linked to pancreatitis in animal and human studies,38 , 39 , 40 suggesting that antioxidants might be beneficial for this disease. One controlled study found that chronic pancreatitis patients consumed diets significantly lower in several antioxidants due to problems such as appetite loss and abdominal symptoms.41 Several controlled studies found lower blood levels of antioxidants, such as selenium, vitamin A, vitamin E, vitamin C, glutathione, and several carotenoids, in patients with both acute and chronic pancreatitis.42 , 43 , 44 , 45 , 46 , 47
There are few controlled trials of antioxidant supplementation to patients with pancreatitis. One small controlled study of acute pancreatitis patients found that sodium selenite at a dose of 500 micrograms (mcg) daily resulted in decreased levels of a marker of free radical activity, and no patient deaths occurred.48 In a small double-blind trial including recurrent acute and chronic pancreatitis patients, supplements providing daily doses of 600 mcg selenium, 9,000 IU beta-carotene, 540 mg vitamin C, 270 IU vitamin E, and 2,000 mg methionine significantly reduced pain, normalized several blood measures of antioxidant levels and free radical activity, and prevented acute recurrences of pancreatitis.49 These researchers later reported that continuing antioxidant treatment in these patients for up to five years or more significantly reduced the total number of days spent in the hospital and resulted in 78% of patients becoming pain-free and 88% returning to work.50 Another double-blind study using similar amounts of selenium, beta-carotene, vitamin C, vitamin E, and methionine as those in the study mentioned above reported significant improvements in pain and overall health in patients with chronic pancreatitis.51
|6 mg daily of natural beta-carotene during periods of high sun exposure||Supplementing with beta-carotene may help protect the skin from ultraviolet rays and sunburn.|
6 mg daily of natural beta-carotene during periods of high sun exposure
Antioxidants may protect the skin from sunburn due to free radical–producing ultraviolet rays.52 Combinations of 1,000 to 2,000 IU per day of vitamin E and 2,000 to 3,000 mg per day of vitamin C, but neither given alone, have a significant protective effect against ultraviolet rays, according to double-blind studies.53 , 54 , 55
Oral synthetic beta-carotene alone was not found to provide effective protection when given in amounts of 15 mg per day or for only a few weeks’ time in larger amounts of 60 to 90 mg per day, but it has been effective either in very large amounts (180 mg per day) or in smaller amounts (30 mg per day) in combination with topical sunscreen.56 , 57 , 58 , 59 , 60
Natural sources of beta-carotene or other carotenoids have been more consistently shown to protect against sunburn. One controlled study found that taking a supplement of natural carotenoids (almost all of which was beta-carotene) in daily amounts of 30 mg, 60 mg, and 90 mg gave progressively more protection against ultraviolet rays.61 In another controlled study, either 24 mg per day of natural beta-carotene or 24 mg per day of a carotenoid combination of equal amounts beta-carotene, lutein, and lycopene helped protect skin from ultraviolet rays.62 A preliminary study compared synthetic lycopene (10.1 mg per day), a natural tomato extract containing 9.8 mg of lycopene per day plus additional amounts of other carotenoids, and a solubilized tomato drink (designed to increase lycopene absorption) containing 8.2 mg of lycopene plus additional amounts of other carotenoids. After 12 weeks, only the two tomato-based products were shown to give significant protection against burning by ultraviolet light.63
Still other trials have tested combinations of several antioxidants. One preliminary study found that a daily combination of beta-carotene (6 mg), lycopene (6 mg), vitamin E (15 IU), and selenium for seven weeks protected against ultraviolet light.64 However, a double-blind trial of a combination of smaller amounts of several carotenoids, vitamins C and E, selenium, and proanthocyanidins did not find significant UV protection compared with placebo.65 Similarly, in a controlled trial, a combination of selenium, copper, and vitamins was found to be ineffective.66
It should be noted that while protection from sunburn has been demonstrated with several types of orally administered antioxidants, the degree of protection (typically less than an SPF of 2) is much less than that provided by currently available topical sunscreens. On the other hand, these modest effects will provide some added protection to skin areas where sunscreen is also used and will give a small amount of protection to sun-exposed areas where sunscreen is not applied. However, oral protection from sunburn is not instantaneous; maximum effects are not reached until these antioxidants have been used for about eight to ten weeks.67 , 68
Age-Related Cognitive Decline
|50 mg every other day||In one study, long-term beta-carotene supplementation slowed the loss of cognitive function in middle-aged healthy males.|
Age-Related Cognitive Decline
50 mg every other day
In a double-blind trial, supplementation with beta-carotene in the amount of 50 mg every other day for 18 years appeared to slow the loss of cognitive function in middle-aged healthy males. Short-term supplementation (one year) was not beneficial.69
|Refer to label instructions||Though not a treatment for withdrawal, beta-carotene supplementation may be a safe way to correct vitamin A deficiencies common to alcoholics (requires a doctor’s supervision to monitor liver function and avoid damage).|
Although the incidence of B-complex deficiencies is known to be high in alcoholics, the incidence of other vitamin deficiencies remains less clear.70 Nonetheless, deficiencies of vitamin A, vitamin D, vitamin E, and vitamin C are seen in many alcoholics. While some reports have suggested it may be safer for alcoholics to supplement with beta-carotene instead of vitamin A,71 potential problems accompany the use of either vitamin A or beta-carotene in correcting the deficiency induced by alcoholism.72 These problems result in part because the combinations of alcohol and vitamin A or alcohol and beta-carotene appear to increase potential damage to the liver. Thus, vitamin A-depleted alcoholics require a doctor’s intervention, including supplementation with vitamin A and beta-carotene accompanied by assessment of liver function. Supplementing with vitamin C, on the other hand, appears to help the body rid itself of alcohol.73 Some doctors recommend 1 to 3 grams per day of vitamin C.
|Refer to label instructions||People who eat fruits and vegetables rich in beta-carotene have a lower risk of developing cataracts.|
People with low blood levels of antioxidants and those who eat few antioxidant-rich fruits and vegetables have been reported to be at high risk for cataracts.74 , 75
Some,76 but not all,77 studies have reported that people eating more foods rich in beta-carotene had a lower the risk of developing cataracts. Supplementation with synthetic beta-carotene has not been found to reduce the risk of cataract formation.78 It remains unclear whether natural beta-carotene from food or supplements would protect the eye or whether beta-carotene in food is merely a marker for other protective factors in fruits and vegetables high in beta-carotene.
|Refer to label instructions||The antioxidant beta-carotene may reduce free radical damage in the stomach, and supplementing with it has led to improvements in people with gastritis in some studies.|
The antioxidant beta-carotene may reduce free radical damage in the stomach,79 and eating foods high in beta-carotene has been linked to a decreased risk of developing chronic atrophic gastritis.80 Moreover, people with active gastritis have been reported to have low levels of beta-carotene in their stomachs.81 In a preliminary trial, giving 30,000 IU of beta-carotene per day to people with ulcers or gastritis led to the disappearance of gastric erosions.82 In another study, combining vitamin C and beta-carotene also led to improvement in most people with chronic atrophic gastritis.83
|Refer to label instructions||Supplementing with beta-carotene may reduce the likelihood of a heart attack and may improve the outcome for people who have already had a heart attack.|
Blood levels of the antioxidant nutrients vitamins A, C, and E, and beta-carotene are reported to be lower in people with a history of heart attack, compared with healthy individuals.84 The number of free radical molecules is also higher, suggesting a need for antioxidants. Streptokinase, a drug therapy commonly used immediately following a heart attack, enhances the need for antioxidants.85
Taking antioxidant supplements may improve the outcome for people who have already had a heart attack. In one double-blind trial, people were given 50,000 IU of vitamin A per day, 1,000 mg of vitamin C per day, 600 IU of vitamin E per day, and approximately 41,500 IU of beta-carotene per day or placebo.86 After 28 days, the infarct size of those receiving antioxidants was significantly smaller than the infarct size of the placebo group.
Low levels of beta-carotene in fatty tissue have been linked to an increased incidence of heart attacks, particularly among smokers.87 One population study found that eating a diet high in beta-carotene is associated with a lower rate of nonfatal heart attacks.88 However, beta-carotene supplementation may not offer the same protection provided by foods that contain beta-carotene. Most,89 , 90 but not all, trials91 have found that supplemental beta-carotene is not associated with a reduced risk of heart attacks.
HIV and AIDS Support
|Refer to label instructions||Beta-carotene levels have been found to be low in HIV-positive people, supplementing with it may be beneficial.|
HIV and AIDS Support
Beta-carotene levels have been found to be low in HIV-positive people, even in those without symptoms.92 However, trials on the effect of beta-carotene supplements have produced conflicting results. In one double-blind trial, supplementing with 300,000 IU per day of beta-carotene significantly increased the number of CD4+ cells in people with HIV infection.93 In a second double-blind study, supplementing with natural mixed carotenoids equivalent to 120,000 IU of beta-carotene per day significantly prolonged survival times in adults with advanced AIDS who were also receiving conventional therapy and a multivitamin.94 In another trial, however, 300,000 IU per day of beta-carotene had no effect on CD4+ cell counts or various other measures of immune function in HIV-infected people.95
|Refer to label instructions||Sunlight triggers oxidative damage in the eye, which can cause macular degeneration. Beta-carotene protects against oxidative damage and may reduce macular degeneration risk.|
Sunlight triggers oxidative damage in the eye, which in turn can cause macular degeneration.96 Animals given antioxidants—which protect against oxidative damage—have a lower risk of this vision problem.97 People with high blood levels of antioxidants also have a lower risk.98 Those with the highest levels (top 20th percentile) of the antioxidants selenium, vitamin C, and vitamin E may have a 70% lower risk of developing macular degeneration, compared with people with the lowest levels of these nutrients (bottom 20th percentile).99 People who eat fruits and vegetables high in beta-carotene, another antioxidant, are also at low risk.100 Some doctors recommend antioxidant supplements to reduce the risk of macular degeneration; reasonable adult levels include 200 mcg of selenium, 1,000 mg of vitamin C, 400 IU of vitamin E, and 25,000 IU of natural beta-carotene per day. However, a preliminary study found no association between age-related macular degeneration and intake of antioxidants, either from the diet, from supplements, or from both combined.101 Moreover, in a double-blind study of male cigarette smokers, supplementing with vitamin E (50 IU per day), synthetic beta-carotene (about 33,000 IU per day), or both did not reduce the incidence of age-related macular degeneration.102
Sickle Cell Anemia
|Refer to label instructions||Sickle cell anemia patients tend to have low levels of antioxidants, which protect cells from oxygen-related damage. Supplementing with beta-carotene may help correct a deficiency.|
Sickle Cell Anemia
Antioxidant nutrients protect the body’s cells from oxygen-related damage. Many studies show that sickle cell anemia patients tend to have low blood levels of antioxidants, including carotenoids, vitamin A, vitamin E, and vitamin C, despite adequate intake.103 , 104 , 105 , 106 , 107 , 108 Low blood levels of vitamin E in particular have been associated with higher numbers of diseased cells in children109 and with greater frequency of symptoms in adults.110 A small, preliminary trial reported a 44% decrease in the average number of diseased cells in six sickle cell anemia patients given 450 IU vitamin E per day for up to 35 weeks. This effect was maintained as long as supplementation continued.111
How It Works
How to Use It
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.
Where to Find It
Dark green and orange-yellow vegetables are good sources of beta-carotene. It is also available in supplements.
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.112
Best Form to Take
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 prevention113 was not duplicated in studies using synthetic pills.114 In smokers, synthetic beta-carotene has apparently caused an increased risk of lung cancer115 , 116 , 117 and disease of the blood vessels118 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.119
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.120 Also, absorption of 9-cis beta-carotene appears to be poor,121 though some researchers question this finding.122
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 animals123 and humans124 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.125 Israeli researchers have investigated whether the special antioxidant effects of natural beta-carotene might help people suffering from asthma attacks triggered by exercise.126 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.”
Interactions with Supplements, Foods, & Other Compounds
Interactions with Medicines
Certain medicines interact with this supplement.
|Some medicines may increase the need for this supplement.|
|Some medicines interact with this supplement, so they should not be taken together.|
|Some interactions between this supplement and certain medicines require more explanation. Click the link to see details.|
Note: The following list only includes the generic or class name of a medicine. To find a specific brand name, use the Medicines Index.
Beta-carotene supplementation, even in very large amounts, is not known to cause any serious side effects,127 , 128 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.129 Beta carotene supplementation may also decrease blood levels of lutein, another carotenoid.130
Preliminary studies in animals indicate that beta-carotene supplementation, when combined with heavy alcohol consumption, may enhance liver toxicity.131 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.132 Until more is known, persons wishing to use beta-carotene supplements should first consult with their doctor.
1. Stich HF, Rosin MP, Hornby AP, et al. Remission of oral leukoplakias and micronuclei in tobacco/betel quid chewers treated with beta-carotene and with beta-carotene plus vitamin A. Int J Cancer 1988;42:195–9.
2. Garewal HS, Katz RV, Meyskens F, et al. ß-Carotene produces sustained remission in patients with oral leukoplakia. Arch Otolaryngol Head Neck Surg 1999;125:1305–10.
3. Liede K, Hietanen J, Saxen L, et al. Long-term supplementation with alpha-tocopherol and beta-carotene and prevalence of oral mucosal lesions in smokers. Oral Dis 1998;4:78–83.
4. Toma S, Benso S, Albanese E, et al. Treatment of oral leukoplakia with beta-carotene. Oncology 1992;49:77–81.
5. Garewal HS, Meyskens FL Jr, Killen D, et al. Response of oral leukoplakia to beta-carotene. J Clin Oncol 1990;8:1715–20.
6. Lippman SM, Batsakis JG, Toth BB, et al. Comparison of low-dose isotretinoin with beta carotene to prevent oral carcinogenesis. N Engl J Med 1993;328:15–20.
7. Johnson J, Ringsdorf W, Cheraskin E. Relationship of vitamin A and oral leukoplakia. Arch Derm 1963;88:607–12.
8. Stich HF, Mathews B, Sankaranarayanan R, Nair MK. Remission of precancerous lesions in the oral cavity of tobacco chewers and maintenance of the protective effect of ß-carotene or vitamin A. Am J Clin Nutr 1991;53:298S–304S.
9. Stich HF, Rosin MP, Hornby AP, et al. Remission of oral leukoplakias and micronuclei in tobacco/betel quid chewers treated with beta-carotene and with beta-carotene plus vitamin A. Int J Cancer 1988;42:195–9.
10. Omenn GS, Goodman GE, Thornquist MD, et al. Risk factors for lung cancer and for intervention effects in CARET, the Beta-Carotene and Retinol Efficacy Trial. J Natl Cancer Inst 1996;88:1550–9.
11. The Alpha-Tocopherol, Beta Carotene Cancer Prevention Study Group. The effect of vitamin E and beta carotene on the incidence of lung cancer and other cancers in male smokers. N Engl J Med 1994;330:1029–35.
12. Hennekens CH, Buring 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.
13. Doering W von E. Antioxidant vitamins, cancer and cardiovascular disease. N Engl J Med 1996;335:1065 [letter].
14. Ben-Amotz A, Levy Y. Bioavailability of a natural isomer mixture compared with synthetic all-transß-carotene in human serum. Am J Clin Nutr 1996;63:729–34.
15. Yeum K-J, Zhu S, Xiao S, et al. ß-carotene intervention trial in premalignant gastric lesions. J Am Coll Nutr 1995;14:536 [Abstract 48].
16. Johnson EJ, Krinsky NI, Russell RM. Serum response of all-trans and 9-cis isomers of ß-carotene in humans. J Am Coll Nutr1996;15:620–4.
17. Shekelle RB, Liu S, Raynor WJ Jr, et al. Dietary vitamin A and risk of cancer in the Western Electric Study. Lancet1981;2:1185–90.
18. Mathews-Roth MM, Pathak MA, Fitzpatrick TB, et al. Beta-carotene as an oral photoprotective agent in erythropoietic protoporphyria. JAMA 1974;228:1004–8.
19. Nordlund JJ, Klaus SN, Mathews-Roth MM, Pathak MA. New therapy for polymorphous light eruption. Arch Dermatol 1973;108:710–2.
20. Mathews-Roth MM, Pathak MA, Fitzpatrick TB, et al. Beta-carotene as a photoprotective agent in erythropoietic protoporphyria. N Engl J Med 1970;282:1231–4.
21. Mathews-Roth MM. Photoprotection by carotenoids. Fed Proc 1987;46:1890–3 [review].
22. Neuman I, Nahum H, Ben-Amotz A. Prevention of exercise-induced asthma by a natural isomer mixture of beta-carotene. Ann Allerg Asthma Immunol 1999;82:549–53.
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24. Chandra RK. Effect of vitamin and trace-element supplementation on immune responses and infection in elderly subjects. Lancet 1992;340:1124–7.
25. Chavance M, Herbeth B, Lemoine A, et al. Does multivitamin supplementation prevent infections in healthy elderly subjects? A controlled trial. Int J Vitam Nutr Res 1993;63:11–6.
26. Girodon F, Lombard M, Galan P, et al. Effect of micronutrient supplementation on infection in institutionalized elderly subjects: a controlled trial. Ann Nutr Metab 1997;41:98–107.
27. Berger MM, Spertini F, Shenkin A, et al. Trace element supplementation modulates pulmonary infection rates after major burns: a double-blind, placebo-controlled trial. Am J Clin Nutr 1998;68:365–71.
28. Chew BP. Role of carotenoids in the immune response. J Dairy Sci 1993;76:2804–11.
29. Bendich A. Beta-carotene and the immune response. Proc Nutr Soc 1991;50:263–74.
30. Hughes DA, Wright AJ, Finglas PM, et al. The effect of beta-carotene supplementation on the immune function of blood monocytes from healthy male nonsmokers. J Lab Clin Med 1997;129:309–17.
31. Murata T, Tamai H, Morinobu T, et al. Effect of long-term administration of beta-carotene on lymphocyte subsets in humans. Am J Clin Nutr 1994;60:597–602.
32. Santos MS, Meydani SN, Leka L, et al. Natural killer cell activity in elderly men is enhanced by beta-carotene supplementation. Am J Clin Nutr 1996;64:772–7.
33. Santos MS, Leka LS, Ribaya-Mercado JD, et al. Short- and long-term beta-carotene supplementation do not influence T cell-mediated immunity in healthy elderly persons. Am J Clin Nutr 1997;66:917–24.
34. Kazi N, Radvany R, Oldham T, et al. Immunomodulatory effect of beta-carotene on T lymphocyte subsets in patients with resected colonic polyps and cancer. Nutr Cancer 1997;28:140–5.
35. Fuller CJ, Faulkner H, Bendich A, et al. Effect of beta-carotene supplementation on photosuppression of delayed-type hypersensitivity in normal young men. Am J Clin Nutr 1992;56:684–90.
36. Coodley GO, Coodley MK, Lusk R, et al. Beta-carotene in HIV infection: an extended evaluation. AIDS 1996;10:967–73.
37. Fryburg DA, Mark RJ, Griffith BP, et al. The effect of supplemental beta-carotene on immunologic indices in patients with AIDS: a pilot study. Yale J Biol Med 1995;68:19–23.
38. Schoenberg MH, Birk D, Beger HG. Oxidative stress in acute and chronic pancreatitis. Am J Clin Nutr 1995;62:1306S–14S [review].
39. Schulz H, Niederau C, Klonowski-Stumpe H, et al. Oxidative stress in acute pancreatitis. Hepato-Gastroenterology 1999;46:2736–2750 [review].
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