Does Beta-Carotene Causes Lung Cancer?

 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" 

Reasons Why Health and Nutrition Supplementations Are Harmful for Health

https://scientificlogic.blogspot.com/search?q=beta+carotene+increases+lung+cancer+

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.

Imagine a cancerous lung cell as a fragile, damaged ball. If you strike it with a single, concentrated stick, representing high-dose beta-carotene in supplement form, the blow may worsen the damage, possibly sending the ball flying out of control, symbolizing the potential for metastasis or progression.

However, if you surround that same ball with many supportive sticks from all directions, representing the wide array of natural antioxidants found in whole foods like purple sweet potatoes, pumpkins, spinach, and carrots, these diverse compounds can help stabilize the environment around the cell. Together, they prevent erratic movement, reduce oxidative stress, and may even support the body's own repair mechanisms.

Similarly, think of a chair. A single leg sticking out on one corner cannot support any weight. If you try to sit on it, you’ll fall,  just as relying on one isolated antioxidant may destabilize internal balance. But a well-designed chair with four legs, each representing different antioxidants acting synergistically, provides stability, safety, and resilience.

Thus, nature’s design, in the form of whole foods containing a symphony of nutrients in modest concentrations, offers a safer and more harmonious approach than isolating one antioxidant. 

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

Reasons Why Health and Nutrition Supplementations Are Harmful for Health

A lot of health-conscious individuals are in the mistaken belief that taking nutrition and health supplements is health-protective, prevents disease and increases longevity.

As a former senior medical researcher and a nutritionist-clinician, let us have a quick look at this belief that has reaped untold profits for health and pharmaceutical companies world-wide.

But first, take this personally coined adage from me:

“Man Eat Food, Not Nutrients”  

Taking high doses of nutritional supplements instead of obtaining nutrients from a balanced diet can have several adverse effects on health.

 While supplements can be beneficial in certain situations, such as to counteract acute nutritional deficiency diseases, examples beriberi from thiamine (vitamin B1) deficiency, or ariboflavinosis causing stomatitis of the mouth and tongue, cheilosis (chapped and fissured lips) and a scaly rash on the genitalia due to riboflavin (vitamin B2) deficiency.

Vitamin B2 deficiency can also been associated with visual disturbances including night blindness (similar to retinol or vitamin A deficiency), migraine headaches, mild anaemia, and psychological effects including depression, while  pellagra is caused by niacin or vitamin B6 and tryptophan deficiency, scurvy from vitamin C deficiency, rickets due to vitamin D deficiency, and macrocytic anaemia from vitamin B12 deficiencies and so on without us needing to write an entire heavy textbook on nutrition deficiency diseases as nutritionists would during their postgraduate training as a specialist in this area of medicine.

However, vitamin supplementations may be used only for short-term therapeutic purposes, but they should not be used as a substitute for a well-rounded and diverse diet. Here are several reasons why excessive reliance on nutritional supplements can be dangerous and inadvisable. Let us look at least 10 reasons why we can think of here:

1.       Nutrient Imbalance:

1. Overloading on specific nutrients can disrupt the delicate balance of vitamins and minerals in the body, leading to imbalances that may be harmful. For example, excessive intake of one nutrient may interfere with the absorption or utilization of another.

2.       Toxicity Risk:

1. Some vitamins and minerals can be toxic in high doses. Fat-soluble vitamins like A, D, E, and K are stored in the body, and excessive amounts can lead to toxicity. Even water-soluble vitamins like vitamin C can cause adverse effects in high doses.

3.     Incomplete Nutrient Spectrum:

1. Whole foods contain a wide array of nutrients, phytochemicals, and fibre that work synergistically for optimal health. Relying solely on supplements may result in missing out on these beneficial compounds.4

4.       Digestive System Interaction:

1. The process of digestion involves a complex interplay of various nutrients and enzymes. Obtaining nutrients from whole foods allows the body to process them in a way that supplements cannot replicate.
2. Bioavailability:
3. Nutrients in whole foods often have higher bioavailability than those in supplements. The body may not absorb and utilize synthetic nutrients as effectively as those from natural sources.

5.       Lack of Other Essential Compounds:

1. Whole foods provide not only essential vitamins and minerals but also other important compounds like antioxidants, fibre, and phytochemicals that are not present in most supplements. These compounds contribute to overall health and disease prevention.

6.       Interaction with Medications:

1. High doses of certain supplements can interact with medications, either reducing their effectiveness or causing harmful side effects. It's crucial to consult with a healthcare professional before combining supplements with prescribed medications.

7.        Cost and Accessibility:

1. Relying on supplements can be more expensive than obtaining nutrients from a balanced diet. Additionally, not everyone has equal access to nutritional supplements, potentially exacerbating health disparities.

8.        Psychological Dependency:

1. Depending solely on supplements may lead to a mindset where individuals believe they can compensate for an unhealthy diet with pills. This can discourage the adoption of positive dietary habits and lifestyle changes.

9.       Unregulated Supplements:

The supplement industry is not as tightly regulated as the pharmaceutical industry. This lack of oversight can result in variations in the quality and effectiveness of different supplements 

10. Unbalanced Protective Phytochemicals:

There is evidence for instance of certain populations such as smokers and asbestos-exposed workers who took beta-carotene supplements for prevention of lung cancer, but instead landed at even higher risk of lung cancer. One noteworthy study that raised concerns about beta-carotene supplementation and lung cancer risk is the Alpha-Tocopherol Beta-Carotene Cancer Prevention (ATBC) trial.  In that study, conducted among male smokers in Finland, it was found an increased incidence of lung cancer among those who took beta-carotene supplements compared to those who did not.

 It's important to note that these findings were specific to high-risk populations, and the relationship between beta-carotene supplements and lung cancer risk may not apply to the general population or non-smokers.

 

In contrast, dietary intake of foods rich in beta-carotene, such as fruits and vegetables, has not been consistently associated with an increased risk of lung cancer. In fact, a diet rich in fruits and vegetables are generally considered beneficial for overall health, including cancer prevention.

 

Foods rich in beta carotenes are carrots, a type of carotenoid, beta-carotene that gives carrots their orange colour and is a precursor to vitamin A. But carrots also contain alpha carotene, as well as lutein and zeaxanthin that are also carotenoids that contribute to eye health, and also falcarinol, a natural pesticide found in carrots, which may have some anti-cancer properties.

 

Besides carrots, tomatoes are also rich not only in beta-carotene, but also lycopene, a powerful antioxidant and carotenoid responsible for the red colour of tomatoes. Lycopene has been associated with various health benefits, including reducing the risk of certain cancers. Furthermore, tomatoes are also rich in quercetin that is found in other fruits and vegetables. Kaempferol is another flavonoid also found in tomatoes, contributing to their overall antioxidant content.

Other beta-carotene-rich foods, along with other carotenoids-rich foods are sweet potatoes, pumpkin, butternut squash, cantaloupe, spinach and kale.  

We can see these natural foods contain a wide variety of carotenoids, and not just beta-carotene alone. All these act synergically as a family to protect against cancer, and not skewed-up with just beta-carotene alone as with beta-carotene supplementation that would then act just like drugs or agents that may cause cancer as with beta-carotene supplements that increased the risk of lung cancer.

If we use only beta-carotene alone as a food supplement, then it is not surprising we increase the risk of lung and other cancers instead of lowering their risk if we consume foods that have a wide variety of phytochemicals including beta-carotenes and other carotenoids.  

It's imperative to consume a variety of colourful fruits and vegetables to ensure a diverse intake of phytochemicals and other nutrients. Different phytochemicals offer various health benefits, and they often work synergistically in the body. Remember that cooking methods can also affect the availability of these compounds, with some being enhanced by cooking (like lycopene in tomatoes) and others being better preserved in raw forms.

Phytochemicals, also known as phytonutrients, are bioactive compounds found in plants. These compounds are not essential for the growth and development of plants, but they have been found to have various health benefits when consumed by humans. Phytochemicals are responsible for the colour, flavour, and disease resistance of plants, and they also play a role in protecting the human body from certain diseases. There are thousands of different phytochemicals, and they can be classified into several main classes:

1.       Flavonoids: This is one of the largest and most studied classes of phytochemicals. Flavonoids have antioxidant properties and are found in a variety of fruits, vegetables, tea, and red wine. Subclasses of flavonoids include flavanols, flavones, flavanones, flavan-3-ols, anthocyanins, and isoflavones.

2. Carotenoids: Carotenoids are pigments that give fruits and vegetables their red, orange, and yellow colours. They have antioxidant properties and are converted to vitamin A in the body. Common carotenoids include beta-carotene, lutein, and zeaxanthin, found in foods like carrots, sweet potatoes, and leafy greens.
3. Glucosinolates: Found in cruciferous vegetables such as broccoli, Brussels sprouts, and kale, glucosinolates are known for their potential anti-cancer properties. They are broken down into bioactive compounds when the vegetables are chewed or chopped.
4. Alkaloids: This diverse class includes compounds such as caffeine, nicotine, and morphine. Alkaloids have various physiological effects and can be found in plants like coffee, tobacco, and poppies.
5. Saponins: Found in beans, lentils, and other legumes, as well as some fruits and vegetables, saponins have anti-inflammatory and immune-boosting properties. They also have a soap-like quality, which can affect the absorption of cholesterol.
6. Phenolic acids: These are a group of compounds with antioxidant properties. Examples include ellagic acid, found in berries and nuts, and caffeic acid, found in coffee.
7. Terpenes: These are compounds derived from the basic building blocks of isoprene. Terpenes include essential oils found in many plants, such as citrus fruits, and have various health-promoting properties.
8. Phytosterols: These plant-derived compounds have a structure similar to cholesterol and can help lower blood cholesterol levels. They are found in nuts, seeds, and vegetable oils.

It's crucial to note that these classifications are broad, and individual phytochemicals within each class may have unique properties and health benefits. A diet rich in a variety of fruits, vegetables, whole grains, nuts, and seeds can provide a diverse array of phytochemicals.

Before making any decisions about using nutrition supplements to augment the goodness of natural foods like fruits, vegetables, legumes, pulses, nuts and cereal grains, especially in the context of specific health conditions, it's advisable to consult with a healthcare professional especially a well-qualified nutritionist who would be able to provide personalized advice based on our individual health status and needs. Additionally, research in the field of nutrition and health is ongoing, so staying informed about the latest scientific developments is always a good practice.

Just remember, all water-soluble vitamins like B1, B2, C and B12 will lose into the urine when taken in excess than the body can retain, and all fat-soluble vitamins like vitamins A, D, E, and K that cannot be excreted in the urine when taken in excess than what the body requires may damage the liver.

One example is the polar bear liver. The livers of polar bears and other arctic animals that are known to be toxic.  Eskimos often eat polar bear meat, but strictly avoid consuming the bear's liver. Polar bear liver toxicity was first reported by Europeans in 1597 when the Dutch explorer Gerrit de Veer wrote in his diary that while taking refuge during the winter in Nova Zemlya (an archipelago in the Arctic Sea in northern Russia) that he and his men became seriously ill after eating polar bear liver.

Since that early report, other similar reports of arctic explorers becoming ill and even dying after consuming polar bear liver have appeared. So why is polar bear liver so toxic? For decades the finger has been pointed at vitamin A. A single polar bear liver (about 500 g) has an astonishing 9 million IU of vitamin A, and acute human toxicity occurs at about 300,000 IU! Long-term (chronic) toxicity can be achieved by ingesting 4000 IU/kg every day for 6–15 months. Therefore, a 90-kg (about 200-lb) man would have to ingest 360,000 IU every day to achieve toxicity. 

 

“Let food in moderation be thy medicine, not nutritional supplements”.

 

“Man eat food, and NOT nutrients” (JB Lim)