For Patients & Caregivers
How It Works
There is no definitive evidence to support use of beta-carotene supplements for preventing cardiovascular disease or cancer.
Beta-carotene is an antioxidant that is found in yellow and orange fruits, such as apricots, cantaloupe, and papaya, as well as squash, carrots, sweet potatoes, pumpkin, leafy greens, and broccoli.
High dietary intake of fruit and vegetables has been associated with reduced risk of cancer and heart disease. Although beta-carotene supplements do not appear to prevent or effectively treat either of these diseases, beta-carotene obtained from the diet may be beneficial. This is because it may interact with other phytochemicals in fruits and vegetables and have a greater effect on the body than do supplements.
- As an antioxidant Several studies support this use.
- To prevent cancer Available evidence does not support the use of beta carotene supplements for preventing cancer. In fact, high beta-carotene intake has been linked to higher risk of lung cancer in male smokers and aggressive prostate cancer.
- To prevent and treat heart disease Several large and well-designed clinical trials and population studies show that taking beta-carotene supplements does not reduce the risk of myocardial infarction (heart attack), angina, or coronary artery disease. In fact, a review of clinical trials showed that beta-carotene was associated with a small increase in overall death as well as death to cardiovascular disease.
- To prevent cataracts Clinical trials generally have shown that taking beta-carotene supplements does not reduce the risk of developing cataracts, but a small study found that amounts of beta-carotene in the blood were associated with decreased cataracts, indicating that beta-carotene obtained from the diet, but not supplements, may be helpful.
- To prevent and treat macular degeneration One clinical trial suggested that taking an antioxidant supplement plus zinc reduces the risk of macular degeneration, but it is not clear whether beta-carotene, or any of the other antioxidants in this supplement, were responsible for these effects.
- To treat AIDS Although small studies have suggested that beta-carotene supplements could increase CD4 cell counts, clinical trials have not been able to replicate these results.
- To stimulate the immune system Some laboratory experiments show that beta-carotene stimulates certain aspects of the immune system, but it is not certain that this effect occurs in the human body.
- To treat oral leukoplakia Several clinical trials have shown that beta-carotene supplementation can induce remission of oral leukoplakia, a pre-cancerous lesion in the mouth.
- To treat type 2 diabetes Data are conflicting.
- To improve cognition Clinical findings suggest that long-term supplementation with beta-carotene may improve cognition.
For Healthcare Professionals
A natural pigment synthesized by plants, beta-carotene is used as an antioxidant, as an immunostimulant, and to prevent or treat cancer, AIDS, heart disease, and leukoplakia. Beta-carotene, along with alpha-carotene and beta-cryptoxanthin, can be converted to retinol and is classified as a provitamin A carotenoid. Supplementation with beta-carotene does not increase overall vitamin A levels or lead to vitamin A toxicity.
Available data of beta-carotene supplementation for HIV-positive patients and its effects on CD4 counts (10) as well as cardiovascular disease are conflicting. A meta-analysis demonstrated a small but significant increase in all-cause mortality and cardiovascular death for the beta-carotene arm over placebo (11), whereas other studies reported no such effects (39) nor any benefits of beta-carotene supplementation against cardiovascular disease (12), or its risk factors (13). However, higher intake of fruits and vegetables, but not antioxidant supplements, was associated with reduced risk of cardiovascular disease, total cancer, and all-cause mortality (44). Beta-carotene has also been inversely correlated with metabolic syndrome (45).
Another meta-analysis did not find any correlation between beta-carotene supplementation and hematologic malignancies (46). Consistent associations between serum beta-carotene levels and risk of developing type 2 diabetes are lacking as well (14) (15).
Additional studies have reported serum beta-carotene to be inversely associated with the incidence of cataract formation (16); higher intake of β-carotene (while avoiding vitamin C supplements) to be associated with lowered risk of acquired hearing loss in women (40); and high dietary intake to have a protective effect on buccal cells from relative telomere length (RTL) shortening (41). Data on the effects of supplementation for preventing cognitive decline are conflicting (17) (50) (51).
Epidemiological associations between beta-carotene and cancer risk are conflicting. Whereas high dietary intake was associated with reduced risk of cervical cancer (1); and limited evidence suggesting an inverse association with overall survival in breast cancer patients (47), high serum levels were correlated with increased risk of aggressive prostate cancer (2), but with reduced risk of aggressive urothelial cell carcinoma (32). Findings of beta-carotene and chemoprevention are inconsistent as well. Consumption of beta carotene, vitamins A, C, fruits and vegetables did not influence the risk of renal cell carcinoma (31); supplementation with antioxidants, beta-carotene and vitamins A, C, and E, did not prevent gastrointestinal cancer, and beta-carotene may actually increase overall mortality (3) (4). Data from large, multi-center trials suggest that supplementation may not lower the risk of prostate cancer (5) (6); and in male smokers over the age 40, it may increase lung cancer incidence (7) (30) (42), regardless of the tar or nicotine content of cigarettes smoked (48). When combined with cigarette smoking, beta-carotene supplements may also reduce the efficacy of cancer therapies, resulting in increased recurrence and mortality (8). Additional data from a large-scale cohort study suggest that alcohol consumption, too, has a negative effect on the chemopreventive property of beta-carotene (9).
Furthermore, long-term supplementation may not have a meaningful effect on total or cancer mortality more than a decade after supplementation ends (49). The U.S. Preventive Services Task Force (USPSTF) recommends against beta-carotene or vitamin E supplements for the prevention of cardiovascular disease or cancer (33).
Mechanism of Action
Beta-carotene has strong antioxidant effects, and protects lipid peroxidation and provitamin-A activity, thereby preventing oxidative damage (34). It was also shown to alleviate the severity of ulcerative colitis in a murine model by modulating several molecular targets including nuclear factor-kappa B, cyclooxygenase-2, interleukin 17, and connective tissue growth factor (35).
In other studies, beta-carotene reduced cell growth and induced apoptosis in a variety of cancer cell lines through caveolin-1 expression (20). It also induces glutathione production (21); enhances macrophage function and natural killer (NK) cell cytotoxicity; and increases T-helper lymphocyte counts. However, clinical findings suggest that beta-carotene can increase cancer risk. It was shown to induce angiogenic gene expression in human umbilical vein endothelial cells (HUVEC) as well as HUVEC migration (22); and stimulate cellular proliferation in pancreatic ductal adenocarcinoma (23) as well as in lung cancer cells (24). Animal studies show that beta-carotene also promotes the development of pulmonary adenocarcinoma via increased cAMP signaling (29).