Beta-carotene is the main safe dietary source of vitamin A, essential for normal growth and development, immune system function, healthy skin and epithelia and vision (1).
Beta-carotene has antioxidant properties that can help neutralize free radicals – reactive oxygen molecules potentially damaging lipids in cell membranes, proteins and DNA. All these changes and a high oxidative stress may lead to the development of cardiovascular disease, chronic inflammation and cancer (2).
At present, it is unclear whether some beneficial effects of beta-carotene and other carotenoids in humans are a result of their antioxidant activity or other non-antioxidant mechanisms. Since many years the results of human studies are conflicting. Dozens of epidemiological studies correlate the intake of carotenoids, especially beta-carotene, alpha-carotene, lycopene and beta-cryptoxanthin with a lower incidence of cancer, cardiovascular events, chronic inflammation and other chronic diseases. The data from some human intervention trials with carotenoids look neutral or even point to a higher disease risk.
In vitro studies indicate that carotenoids can also inhibit the oxidation of fats under certain conditions. They may have anti-atherosclerotic potential, but their effects in humans appear to be more complex (3).
Beta-carotene and other carotenoids can facilitate communication between neighboring cells by stimulating the synthesis of proteins that form pores in cell membranes, allowing communication through the exchange of small molecules (4). This effect appears unrelated to the vitamin A or antioxidant activities of various carotenoids (5).
From animal experiments and from association studies it became evident that carotenoids should have a positive effect on adipose tissue, liver fat and other metabolic parameters. Recently A. Canas et al. published data which prove the beneficial effect of mixed carotenoids on adiposity in children (70). Most of the metabolic parameters, including BMI, visceral adipose tissue and subcutaneous adipose tissue mass decreased and correlated with increasing beta-carotene plasma levels.
Some clinical trials have found that beta-carotene supplementation improves several parameters of immune function, such as increasing the number of white blood cells and the activity of natural killer cells (6, 7, 8). Nevertheless, as vitamin A is essential for normal immune system function, it is difficult to determine whether the effects of beta-carotene are related to their vitamin A activity or other activities of carotenoids.
Emerging data in the carotenoid field are presented for cognitive health. A report from the Physicians’ Health study II stated that a long-term supplementation with beta-carotene improved verbal memory and cognitive function overall (71). Other studies could not show the same effect, probably because a treatment period of 18 years can never be repeated again in a human trial as it was done in the Physicians’ Health Study I and II.
For another carotenoid, lutein, the impact on cognitive health, above all, neural processing speed, improved memory and attention is established (74,75).
Authored by Dr Peter Engel in 2010, reviewed and revised by Dr. Adrian Wyss on 08.10.17.