The results of early observational studies suggest a decrease in lung cancer risk due to dietary beta-carotene intake (9, 10).
Two large prospective cohort studies that followed more than 120,000 men and women for at least ten years revealed no significant association between dietary beta-carotene intake and lung cancer risk (11). However, participants with the highest intakes of total carotenoids were at significantly lower risk of developing lung cancer than those with the lowest intakes.
An analysis of the pooled results of six prospective cohort studies in North America and Europe found no relationship between dietary beta-carotene intake and lung cancer risk (12).
A review of prospective cohort studies concluded that any protective effect of dietary carotenoids against the development of lung cancer is likely to be small and not statistically significant (13).
Two clinical studies indicated that long-term high-dose beta-carotene supplementation (20 mg/day and more over several years) in heavy smokers and former asbestos workers increased the risk of lung cancer and death. The reasons for such findings in these high-risk groups cannot be fully explained yet, however the research from X.-D. Wang’s group at Tufts University are giving some explanations. (see also Safety).
Giving up smoking ─ rather than increasing beta-carotene intake ─ is without doubt the best way of protecting against lung cancer.
A number of case-control studies have found higher blood levels of dietary beta-carotene and other carotenoids, potentially preventing the oxidation of low-density lipoprotein (LDL), to be associated with significantly lower risk of atherosclerosis (14, 15, 16, 17, 18, 19).
Higher plasma carotenoids at baseline have been associated with significant reductions in the risk of cardiovascular disease in some prospective studies (20, 21, 22, 23, 24) but not in others (25, 26, 27, 28). It is not yet clear whether this effect is a result of carotenoids or other factors associated with diets high in carotenoid-rich fruits and vegetables.
In contrast, four randomized controlled trials found no evidence that beta-carotene supplements in doses ranging from 20 to 50 mg/day were effective in preventing cardiovascular diseases (29, 30, 31, 32).
Some evidence points to a role of beta-carotene in protecting the skin from sun damage. Beta-carotene ─ both alone and in combination with other carotenoids or antioxidant vitamins ─ can be used as an oral sun protection ─ in addition to topical sunscreens ─ for the prevention of sunburn (33). It was demonstrated that supplementation with beta-carotene protects from UV-induced erythema (72). Similarly intake of beta-carotene and other carotenoids improve several parameters of skin structure and protect from photoaging (73).
Cataracts, a clouding in the crystalline lens of the eye causing vision loss if untreated, can develop from long-term exposure to ultraviolet light. Evidence from epidemiological studies that cataracts were less prevalent in people with high dietary intakes of carotenoids absorbing ultraviolet light (see also lutein and zeaxanthin) led to the inclusion of beta-carotene supplements in several large randomized controlled trials of antioxidants.
While some studies found that beta-carotene supplementation decreased the risk of cataracts (34, 35) others did not (36).
In a number of studies beta-carotene supplementation was found to enhance certain immune responses: some clinical trials have found that beta-carotene supplementation improves several biomarkers of immune function. It can lead to an increase in the number of white blood cells and the activity of natural killer cells. Both of these are important in combating various infectiousdiseases.
It may be the case that beta-carotene stimulates the immune system once it has undergone conversion to vitamin A. Another explanation could be that the antioxidant actions of beta-carotene protect cells of the immune system from damage by reducing the toxic effects of free radicals (8).
Authored by Dr Peter Engel in 2010, reviewed and revised by Dr. Adrian Wyss on 10.10.17 .
