Beta Carotene and Smoking: Increased Lung Cancer Risk
Examining how beta carotene supplements may raise lung cancer risk, especially among people who smoke or have a history of smoking.
Beta carotene—a compound found naturally in many fruits and vegetables—has long been associated with positive health effects due to its antioxidant properties. However, research over recent decades has revealed a concerning link between beta carotene supplementation and increased lung cancer risk, particularly among people who currently smoke or have smoked in the past. This article explores the evidence, underlying mechanisms, and recommendations surrounding this counterintuitive health risk.
The Cancer Risk of Beta Carotene Use and Smoking
Lung cancer remains the second most common type of cancer in both men and women, and is the leading cause of cancer-related deaths in the United States. Scientists have directed substantial effort toward prevention, with a key area of focus on whether antioxidant supplementation, such as beta carotene, could reduce cancer risk. Antioxidants are thought to fight oxidative stress, which theoretically should protect against cancer. Yet, large clinical trials have shown otherwise for certain populations.
Key Clinical Trials Linking Beta Carotene and Cancer Risk
- Two important clinical trials in the 1990s—the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) Study and the Carotene and Retinol Efficacy Trial (CARET)—showed a higher incidence of lung cancer among people who took beta carotene supplements and who smoked.
- A 2022 analysis of another major clinical trial reinforced these findings, demonstrating a significant association between beta carotene supplementation and higher lung cancer rates in people with a history of smoking over a 10-year follow-up.
These results were surprising because observational studies had previously suggested that eating foods rich in beta carotene (like carrots and leafy greens) was linked to lower cancer rates. The clinical trials, involving supplement pills rather than food, demonstrated the opposite effect for high-risk groups such as smokers.
U.S. Preventive Services Task Force Review
In 2022, the U.S. Preventive Services Task Force (USPSTF) conducted a comprehensive review of research on vitamin and mineral supplements for cancer prevention. Here’s what they found about beta carotene:
- An analysis of six large clinical trials—including the ATBC and CARET trials—showed beta carotene supplements were associated with a 20% increased risk of lung cancer.
- The increased risk was strongest among those already at higher risk for lung cancer, such as current and former smokers.
- As a result, the USPSTF recommended against the use of beta carotene supplements for cancer prevention in general, and especially for people who smoke.
How Beta Carotene May Increase Lung Cancer Risk in Smokers
What others are reading
The exact mechanism by which beta carotene supplementation raises lung cancer risk in smokers is not fully understood. However, several hypotheses have been proposed by researchers:
- Interaction with cigarette smoke: Heavy smoking may impair normal pathways associated with beta carotene in the body, possibly turning this antioxidant into a pro-oxidant in the lung tissue instead. This effect would counteract the potential protective benefits and might promote the development of cancer.
- Tar and nicotine as contributing factors: Tar contains many carcinogenic compounds that interact with antioxidants. Yet, research (such as the 2018 study on supplement use and risk) indicates that the increased cancer risk from beta carotene supplements occurs regardless of the amount of nicotine or tar consumed, suggesting other complex interactions at play.
- Cellular and genetic changes: In laboratory models, beta carotene—when exposed to cigarette smoke—can lead to oxidative breakdown and may ultimately damage the DNA in lung cells, increasing the risk of tumor formation.
Evidence From the ATBC Study
The ATBC study, which involved over 29,000 male smokers aged 50–69 in Finland, randomized participants to receive either alpha-tocopherol (vitamin E), beta carotene, both, or a placebo. The findings showed:
- Those who took beta carotene supplements had a significantly higher risk of developing lung cancer in all categories of cigarette tar and nicotine content.
- The increased risk ranged from a 22% to 31% higher chance of lung cancer depending on cigarette tar or nicotine level, but the increased risk was not limited to those who smoked cigarettes with higher tar or nicotine.
| Cigarette Type | Relative Risk Increase (with Beta Carotene) |
|---|---|
| Ultralight (≤7 mg tar) | 31% |
| Nonfiltered (≥21 mg tar) | 22% |
| Lowest nicotine (≤0.8 µg) | 23% |
| Highest nicotine (≥1.3 µg) | 22% |
This pattern suggests the risk associated with beta carotene supplementation is independent of the specific type of cigarette smoked.
Statistical Evidence: What Meta-Analyses and Reviews Report
To understand the scope of the risk, several large meta-analyses of randomized clinical trials—including as many as 18 studies—have been published in the past few years. Their key findings include:
- No significant association between beta carotene supplementation and overall cancer incidence when considering all cancers and all people.
- A statistically significant increase in lung cancer risk (risk ratio up to 1.19) for people who take beta carotene supplements, especially for smokers and those who consumed lower doses over time.
- No clear evidence of risk increase for other types of cancer.
Why Don’t Foods High in Beta Carotene Carry the Same Risk?
Observational and epidemiological studies have long suggested that diets rich in fruits and vegetables—many of which are excellent sources of beta carotene—are associated with lower overall cancer risk. However, this protective effect does not translate to the use of high-dose beta carotene supplements. Possible reasons include:
- Foods contain a complex mixture of nutrients and antioxidants, which may work in concert to protect the body from cancer, whereas supplements provide isolated, high doses of a single nutrient.
- Concentrated beta carotene from supplements may have different chemical behaviors in the body—especially under stress conditions such as chronic smoke exposure—potentially causing harm rather than help.
Expert Recommendations and Guidelines
Based on the accumulated evidence, major organizations and health authorities have issued several recommendations:
- People who smoke or have smoked (even in the past) should not take beta carotene supplements. This group faces the greatest documented increase in lung cancer risk.
- The general population is advised not to rely on beta carotene supplements for cancer prevention, as there is no evidence of benefit and potential evidence of harm.
- Diets rich in fruits and vegetables continue to be recommended for overall health and potential cancer prevention, as whole foods offer a complex array of beneficial compounds that cannot be matched by isolated supplements.
Summary Table: Beta Carotene Supplements and Lung Cancer Risk
| Finding | Detail |
|---|---|
| Increased Lung Cancer Risk | 20-31% higher risk in smokers taking beta carotene supplements |
| Tar/Nicotine Dependency | Risk increase is independent of cigarette tar or nicotine content |
| General Cancer Risk | No effect on overall cancer incidence in non-smokers |
| Food Sources | No conclusive evidence of increased risk from beta carotene-containing foods |
Common Sources of Beta Carotene
- Carrots
- Sweet potatoes
- Spinach
- Kale
- Cantaloupe
- Butternut squash
- Red and yellow peppers
Remember, the risk identified in scientific studies relates to supplemental beta carotene, not naturally occurring beta carotene in foods.
Key Takeaways
- Beta carotene supplements should be avoided by people who smoke or have smoked due to a documented increase in lung cancer risk.
- There is no current evidence supporting the use of beta carotene supplements for cancer prevention in the general population.
- Diets rich in fruits and vegetables remain recommended for reducing overall disease risk.
Frequently Asked Questions (FAQs)
Does eating foods high in beta carotene increase my cancer risk if I smoke?
No. The increased risk is associated specifically with supplements, not foods naturally high in beta carotene. Whole foods are safe and part of a healthy diet.
Can beta carotene supplements reduce my risk of developing lung cancer?
No. In fact, studies have found the opposite—beta carotene supplementation increases lung cancer risk in smokers or people with a history of smoking.
Is it safe to take multivitamins if I am a smoker?
Most multivitamins contain smaller quantities of beta carotene than high-dose supplements, but it is essential to read labels. People who smoke or have smoked should avoid any product containing significant amounts of beta carotene unless directed by a healthcare professional.
What if I used to smoke, but quit years ago?
The largest increases in risk have been seen in current smokers and recent ex-smokers, but some studies suggest the risk might persist for people who smoked in the past. The best strategy is to avoid beta carotene supplements altogether if you have any smoking history.
Are other antioxidant supplements risky for smokers?
Current evidence particularly implicates beta carotene. The effects of other antioxidant supplements are still being studied, but it is safest to consult a healthcare provider before using any supplement, particularly if you are at higher risk for cancer.
What should I do if I’m worried about my lung cancer risk?
Quit smoking if you haven’t already, avoid high-dose beta carotene supplements, and talk to your healthcare provider about lung cancer screening if you are at higher risk. Focus on a healthy diet rich in fruits, vegetables, and whole grains.
References
- Large clinical trials (ATBC, CARET)
- U.S. Preventive Services Task Force guidelines
- Recent meta-analyses of randomized controlled trials
References
- https://www.healthline.com/health/lung-cancer/beta-carotene-and-smoking
- https://pmc.ncbi.nlm.nih.gov/articles/PMC6636175/
- https://pubmed.ncbi.nlm.nih.gov/36715090/
- https://www.healthline.com/health/lung-cancer/smoking-lung-cancer
- https://acsjournals.onlinelibrary.wiley.com/doi/full/10.1002/cncr.23527
- https://www.mayoclinic.org/drugs-supplements/beta-carotene-oral-route/description/drg-20066795
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