For Patients & Caregivers
How It Works
Beta-carotene is not effective in treating heart disease, cancer, or HIV or preventing cataracts or macular degeneration.
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. Although scientists have proposed a number of mechanisms by which beta-carotene obtained through a healthy diet may prevent cancer, current evidence does not support supplementation.
- As an antioxidant
Several studies support this use.
- To prevent cancer
Several large and well-designed clinical trials do 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. (This does not necessarily apply to beta carotene obtained from the diet. Beta carotene may act in conjunction with other phytochemicals in fruits and vegetables).
- 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 clinical 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 treat HIV and AIDS
Although a few small studies suggested that beta-carotene supplements could increase CD4 cell counts, recent 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. No clinical trials have tested this use in healthy volunteers.
- 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 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
One clinical study found that high serum beta-carotene levels decreased risk of developing type 2 diabetes, but another study found that beta-carotene supplements did not reduce the risk for type 2 diabetes. Further studies of dietary beta-carotene are needed.
- To improve cognition
Results from a clinical trial suggest that long-term supplementation with beta-carotene may improve cognition; however, because of the possible health risks associated with beta-carotene supplementation, further studies are needed to determine if dietary beta-carotene could also improve cognition.
Do Not Take If
- In general, high dietary intake of fruit and vegetables is associated with reduced risks 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 more 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 alone.
For Healthcare Professionals
A natural pigment synthesized by plants, beta-carotene is used as an antioxidant and an immunostimulant, and to prevent or treat cancer, HIV, 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. Animal studies show that beta-carotene promotes the development of pulmonary adenocarcinoma via increased cAMP signaling (29).
Available data concerning beta-carotene supplementation for HIV-positive patients and its effects on CD4 counts (10) as well as cardiovascular disease are conflicting. A meta-analysis of eight randomized trials demonstrated a small but significant increase in all-cause mortality and cardiovascular death for the beta-carotene arm over placebo (11), whereas other studies have reported no benefits of beta-carotene supplementation on cardiovascular disease (12) or its risk factors (13).
Consistent associations between serum beta-carotene levels and risk of developing type 2 diabetes are also lacking (14) (15). One study reported that serum beta-carotene was inversely associated with the incidence of cataract formation (16).
Long-term beta-carotene supplementation may increase cognitive function (17).
Epidemiological associations between beta-carotene and cancer risk are conflicting. Whereas high dietary beta-carotene intake was associated with reduced risk of cervical cancer (1), high serum levels were also associated with increased risk for aggressive prostate cancer (2) but decreased the risk of aggressive urothelial cell carcinoma (32). In addition, studies of beta-carotene supplementation and chemoprevention for cancer are inconsistent. Studies show that consumption of beta carotene, vitamins A, C, fruits and vegetables does not influence the risk of renal cell carcinoma (31). A review of 14 clinical trials shows that supplementation with antioxidants, beta-carotene and vitamins A, C, and E, does not prevent gastrointestinal cancer, and that beta-carotene may actually increase overall mortality (3) (4). Data from large, multicenter trials suggest that beta-carotene 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). Beta-carotene supplementation especially when combined with cigarette smoking may also reduce the efficacy of cancer therapies, resulting in increased recurrence and mortality (8). A large-scale cohort study in the Netherlands suggests alcohol consumption has a negative effect on the chemopreventive property of beta-carotene (9).
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. It protects lipid peroxidation and provitamin-A activity, thereby preventing oxidative damage (34). It was also shown to alleviate the severity of ulcerative colitis in mice 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 possibly through caveolin-1 expression (20). In vivo studies suggest that beta-carotene induces glutathione production (21). Beta-carotene may enhance macrophage function and natural killer (NK) cell cytotoxicity and increase T-helper lymphocyte counts. However, recent clinical studies suggest that beta-carotene can increase cancer risk, and in vitro studies have shown that beta-carotene induces angiogenic gene expression in human umbilical vein endothelial cells (HUVEC) as well as HUVEC migration (22). Furthermore, beta carotene stimulated cellular proliferation in a pancreatic ductal adenocarcinoma cell line (23) and in lung cancer cells (24).