My nephew, Professor Dr Ong Wei Yi , a neuroscientist at the National University of Singapore casually mentioned in a family WhatsApp group on Wednesday, 2 July, 2025 this:
I quote what he said in inverted comma in pink
"Excessive consumption of beta carotene in smokers actually increases the risk of lung cancer, not decreases. So a certain level of free radicals may act against cancer cells too"
Yes, I am aware of this a long time ago.
Actually I have already written on that on Wednesday, December 20, 2023 here"
Unfortunately, the hundreds of articles on various subjects I write here, seldom do readers respond to them. I am unsure if they even understand what I am trying to tell, else I waste a lot of my time and effort.
Let me respond again with greater detail that touches on a fascinating and important area of nutritional science and cancer risk, especially regarding beta-carotene, a precursor to vitamin A and a powerful antioxidant. Let us look at the science-based answer and distinguish between food sources and supplements, as well as smokers vs. non-smokers.
Smokers and Beta-Carotene: The Risk of Lung Cancer
Indeed, there is an increased lung cancer risk with high-dose beta-carotene supplementation in smokers is a well-established finding based on major clinical trials. This was shown in these key studies:
1. ATBC Study (Alpha-Tocopherol, Beta-Carotene Cancer Prevention Trial) – Finland, 29,000 male smokers:
20 mg/day beta-carotene for 5–8 years. Increased incidence of lung cancer by ~18% in the supplemented group.
2. CARET Study (Beta-Carotene and Retinol Efficacy Trial) – U.S., smokers & asbestos-exposed workers:
25 mg/day beta-carotene + 25,000 IU retinyl palmitate.
Trial was stopped early because of a 28% increase in lung cancer. The reason is, in smokers, the lungs already face oxidative stress from cigarette smoke. Beta-carotene may act as a pro-oxidant under this stress rather than an antioxidant, causing DNA damage instead of protection. Beta-carotene supplements at high doses are harmful in smokers and should be avoided.
What About Natural Foods Like Carrots for Smokers?
There is no strong evidence to suggest that eating carrots or other beta-carotene-rich foods (like sweet potatoes, spinach, pumpkin) increases lung cancer risk, even in smokers. The reason is, natural foods contain a complex mix of antioxidants, vitamins, and phytochemicals that work synergistically. The beta-carotene content is much lower compared to supplements. The body regulates the conversion of beta-carotene from food into vitamin A as needed.
Epidemiological studies even show that diets high in fruits and vegetables may be protective for general health, including some cancers . although this protection is reduced or negated in heavy smokers.
Non-Smokers and Excessive Beta-Carotene
For non-smokers, natural food sources of beta-carotene are safe, even in large quantities. High-dose supplements are generally not needed unless medically indicated, and may not provide any extra benefit. Too much beta-carotene from food may turn the skin slightly orange (carotenemia), especially in children, but this is harmless and reversible.
There is no solid evidence showing increased lung cancer risk in non-smokers from beta-carotene, whether from food or supplements , but the benefits of supplementation remain unclear, and moderation is wise. Thus I agree that beta-carotene supplements at high doses are harmful in smokers and should be avoided, but there is no strong evidence to suggest that eating carrots or other beta-carotene-rich foods (like sweet potatoes, spinach, pumpkin) increases lung cancer risk, even in smokers let alone for non smokers
In short, we should not discourage smokers and non-smokers from eating foods rich in beta carotene that also has a wide variety of other antioxidants because there is no evidence to suggest that these foods cause lung or other cancers. Maybe only for high doses of stand-alone beta-carotene found artificially in food supplements, but not in low doses found in natural foods. Overall all, naturally coloured fruits and vegetables are exceedingly protective against all chronic diseases, not just against cancers.
My conclusion is beta-carotene from supplements may not be safe for smokers, but beta-carotene from food (e.g. carrots) may be safe even for smokers. But for non-smokers avoid unnecessarily high doses from supplements, but safe and possibly beneficial from natural sources like carrots, sweet potatoes, spinach, pumpkin and even tomatoes too that contains lycopene and other carotenoids that has been shown in numerous animal studies to protect against prostate cancer.
The main cause of lung cancer is smoking and lesser due to asbestos exposure. So stop smoking and let the body recover naturally and not blame it on beta-carotene supplements or found naturally in foods
