Many years ago, a study was published in which smokers were given beta-carotene – for the prevention of lung cancer. But then they did not get sick less often, but even more often with lung cancer. Once this unpleasant side effect was noticed, the study was stopped immediately and smokers were advised to stop taking beta-carotene. Meanwhile, however, it has come to the point where some people believe that dietary beta carotene (such as carrots) is harmful and can cause lung cancer. We explain how it behaves.
What is beta-carotene?
Beta carotene is a phytochemical in the carotenoid family. Carotenoids, in turn, are fat-soluble plant substances with yellow to red coloring. A diet rich in carotenoids is therefore used when the diet contains a high proportion of yellow and orange or even red vegetables.
Beta-carotene is the best known carotenoid. Hardly any other food is as rich as it is in carrots and kale. Although green cabbage is green and not yellow or orange, the green of chlorophyll covers the orange tones of beta-carotene.
Which carotenoids are there?
Other carotenoids are, for example
- the alpha-carotene (eg in pumpkin and carrots),
- Lycopene (especially in tomatoes),
- the beta-cryptoxanthin (eg in pumpkin and red pepper),
- lutein (eg in savoy cabbage, parsley, and kale),
- Astaxanthin (produced by algae) and
- the zeaxanthin (eg in red pepper).
All of them are considered to be powerful antioxidants that fight free radicals and oxidative stress and can thus prevent many diseases, such as cardiovascular diseases, rheumatic diseases, eye diseases, as well as Alzheimer’s and Parkinson’s and cancer.
Does beta carotene protect against lung cancer?
As late as the 1980s, beta carotene was considered very healthy by all people – whether they were smokers or not. In 1986, even a study on this topic appeared (1,266 participants). They found that smokers who did not eat carrots had a three-fold higher risk of lung cancer than smokers who ate carrots at least once a week. A significantly increased risk of lung cancer also existed for those who only liked little green leafy vegetables. Liver and cheese (vitamin A) did not appear to have a protective effect because those who did not have either had no increased risk of ever developing lung cancer.
Another study (1,663 participants) in the same year showed similar, namely that a carotenoid-rich diet, in particular, smokers protected against lung cancer.
But who wants to bother with all the vegetables? So at least the thought of many smokers, who on the whole rather seldom eat health-conscious. However, since lung cancer is a desirable target for her and smoking cessation is rarely up for debate, the obvious solution was: why not simply take a beta-carotene pill every day? Because it was known that a high level of beta-carotene in the blood reduced the risk of lung cancer. So you could safely take the beta carotene in pill form.
Beta-carotene in pill form increases the risk of lung cancer
In 1996, a study on beta-carotene pills, published in the Journal of the National Cancer Institute, was quickly launched. More than 29,000 men between the ages of 50 and 69 who smoked more than 5 cigarettes a day took 50 mg of vitamin E (alpha-tocopherol ), 20 mg beta carotene, or both, or a placebo supplement for an average of 6 years.
Regarding vitamin E, there was no effect on lung cancer risk. Beta-carotene, however, appeared to increase lung cancer risk (but only slightly), especially in heavy smokers (more than 20 cigarettes per day) compared to smokers who smoked less. Even in men who also indulged in higher alcohol consumption, was due to the beta carotene intake an increased risk of lung cancer.
Study stop because of frequent lung cancer cases
Similar results were obtained by the so-called CARET study, which was published in the same year. Here, over 18,000 participants were given 30 mg beta-carotene daily and 25,000 IU vitamin A or placebo. The study had to be stopped after just 21 months, as the beta carotene group had 28 percent more lung cancers and 17 percent more deaths. The participants of the study were smokers, former smokers or asbestos workers, ie all those with a high risk of lung cancer.
At the same time, there were also studies that did not show any disadvantages after taking beta-carotene, such as the study that also appeared in 1996 (in the New England Journal of Medicine) and found that:
Beta-carotene in pill form does not always harm
More than 22,000 healthy men between the ages of 40 and 84 took 50 mg beta-carotene or placebo every other day for 12 years. These included smokers as well as former smokers and non-smokers. At the end of the 12 years, however, no significant differences in cancer risk, cardiovascular or mortality risk could be identified. In the beta-nicotine group, even fewer men had lung cancer than the placebo group (82 versus 88), which was not statistically significant.
Three years later (1999), a study of nearly 40,000 healthy women – whether smokers or non-smokers – found that dietary supplementation with 50 mg beta-carotene every other day for an average of 2.1 years does not affect the risk of cancer or cardiovascular disease even the mortality had.
Problematic: The long-term use of carotenoids in pill form
But in 2009, another study with a negative outcome emerged: researchers from the University of North Carolina at Chapel Hill found that the long-term use (up to 10 years) of beta-carotene supplements and other carotenoids or vitamins was based on data from more than 77,000 participants -A-containing supplements (retinol and lutein) may increase lung cancer risk, especially in smokers. The study knowledge appeared in the American Journal of Epidemiology.
The scientists were able to observe that the longer they took the supplements, the higher the risk of lung cancer from smokers. The dose of supplements was secondary, even mediocre doses increased the risk of long-term supplementation.
Whether taking these supplements increases the risk of lung cancer in non-smokers was not apparent since hardly any of the non-smokers became ill with lung cancer.
Dr. Jessie Satia, Professor of Epidemiology and Nutrition at the UNC Gillings School of Global Public Health said:
“We believe that the antioxidant beta-carotene at too high a dose has oxidative effects, which then increases the risk of cancer.”
High-carotenoids from carotenoids reduce the risk of lung cancer
More recently, it has been sensible to focus increasingly on the effects of a carotenoid-rich diet rich in vegetables. For example, in Cancer Science in 2014, a study of over 10,000 participants found that high carotenoid levels in the blood (alpha-carotene and beta-cryptoxanthin) were significantly associated with a lower risk of lung cancer death.
Smokers’ lung cancer risk also decreased significantly by 46 percent for high levels of alpha-carotene and 61 percent for high levels of beta-cryptoxanthin.
Even more recent is the study from the University of Montreal / Canada Research Center in 2017. Here, too, increased intake of carotenoid-rich vegetables has been shown to protect against lung cancer (squamous cell carcinoma and adenocarcinoma) – including heavy smokers.
Conclusion: Vegetables protect against lung cancer, carotenoid pills do not do this
Isolated beta-carotene and vitamin A supplements should not be taken by smokers for an extended period of time. In non-smokers, however, they have no harmful effect.
A carotenoid-rich diet consisting of plenty of carrots, squash, peppers, tomatoes, sweet potatoes, herbs (parsley, dill, etc.), kale, spinach, and other green leafy vegetables should be practiced by everyone, as it has been shown to reduce the risk of lung cancer although both non-smokers and smokers (including heavy smokers).
Note: For the sake of completeness, we would like to point out that in a carotenoid-rich diet no vitamin A overdose is to be feared, no matter how many carrots you like to eat. Although some carotenoids can be converted to vitamin A in the body, they can only be produced in the amount required by the body.
It would be quite different if you take cod liver oil or like to eat liver, both of which are very rich in vitamin A. Here, a vitamin A overdose is possible, which should be avoided at all costs – especially in pregnancy, as it can lead to malformations and brain damage in the embryo.