From the Guidelines
Smokers should avoid taking high-dose vitamin A supplements, as they may increase the risk of lung cancer, and instead focus on obtaining vitamin A through a balanced diet. The association between vitamin A and lung cancer in smokers is supported by several studies, including the CARET trial, which found a relative risk of 1.28 for lung cancer in participants taking vitamin A and beta-carotene supplements compared to those taking a placebo 1. This adverse effect is thought to be specific to synthetic supplements rather than vitamin A from food sources. The mechanism likely involves the interaction between beta-carotene, a precursor to vitamin A, and cigarette smoke, creating harmful oxidative compounds in lung tissue that promote cancer development.
Some key points to consider:
- High-dose beta-carotene supplementation, typically 20-30 mg daily, has been shown to increase lung cancer incidence and mortality in current smokers by 16-28% 1.
- The best approach for reducing lung cancer risk remains smoking cessation, which significantly decreases cancer risk over time regardless of previous supplement use.
- Smokers should focus on obtaining vitamin A through a balanced diet including orange and yellow fruits, dark leafy greens, and other natural sources.
- If nutritional supplementation is necessary, smokers should consult healthcare providers about alternatives to high-dose beta-carotene.
- Epidemiologic data support the idea that consuming fruits and vegetables high in vitamin A can lower the incidence of lung cancer, but this benefit is not seen with synthetic supplements 1.
From the Research
Association between Vitamin A and Lung Cancer in Smokers
- The study 2 found that high-dose vitamin A administration reduced the number of new primary tumors related to tobacco consumption and improved the disease-free interval in patients curatively resected for stage I lung cancer.
- However, the systematic review and meta-analysis 3 revealed that there was insufficient evidence overall to support the use of vitamin A or related retinoids for the treatment or prevention of lung cancers, and that retinyl palmitate combined with beta carotene increased the risk of lung cancer in smokers.
- A prospective study 4 found a significant positive association of dietary vitamin A intake with lung cancer risk among current smokers, suggesting that vitamin A may increase the risk of lung cancer in this population.
- Another study 5 found that vitamin A had no clear effect on lung cancer risk, while provitamin A carotenoids such as lutein/zeaxanthin, lycopene, and alpha-carotene displayed a certain protective trend.
- The evidence suggests that the relationship between vitamin A and lung cancer in smokers is complex and may depend on various factors, including the dose and form of vitamin A, as well as the population being studied.
Key Findings
- High-dose vitamin A may reduce the risk of new primary tumors in patients with stage I lung cancer 2.
- Vitamin A may increase the risk of lung cancer in current smokers 4.
- The use of vitamin A or related retinoids for the treatment or prevention of lung cancers is not supported by sufficient evidence 3.
- Provitamin A carotenoids may have a protective effect against lung cancer, while beta-carotene may increase the risk in smokers 5.