Nutraceuticals and nootropics for anti-aging

New beta-carotene study may solve lung puzzle.

Beta-carotene belongs to the large group of compounds known as carotenoids, which are responsible for many of the green, yellow, orange, red, blue, and purple colors in fruits, vegetables, and flowers. Beta-carotene is thought to be an antioxidant, but its primary role in nutrition is as a source of vitamin A — the body converts beta-carotene into vitamin A as needed.

Epidemiological studies and lab studies have long provided evidence of beta-carotene’s physiological actions against cancer, cardiovascular disease, and immune deficiencies.¹ But human clinical studies, in which the impact of long-term beta-carotene supplementation on cardiovascular disease and cancer was examined, have often produced contradictory results.¹ An especially upsetting example is the case of smoking-related lung cancer.

It was shown a quarter century ago that lung cancer risk is lower in smokers and non-smokers who consume more beta-carotene.² Later studies have firmly established this result in animal experiments, but later human studies have resulted in controversy and confusion.^3a Most clinical trials have shown no benefits of beta-carotene in preventing lung cancer. Worse yet, two large trials concluded that beta-carotene consumption actually increases the incidence of lung cancer in smokers.^{3b,4,5a,5b,6a,6b} Consequently, researchers and physicians have for the past ten years been advising smokers to avoid beta-carotene supplements — in effect, giving greater weight to two puzzling clinical trials than to dozens of other studies showing benefits in other contexts and for other kinds of cancer.

An explanation for this enigma may now be in hand. Studies have shown that smokers who consume larger amounts of beta-carotene sustain less pulmonary damage than those who consume less.^3b The latest such evidence was published by a group of researchers at the University of Medicine Bichat, who reported that heavy smokers with low blood levels of beta-carotene suffered far more loss in lung function than those with high beta-carotene levels.^7,8 These results are in good agreement with an explanation for the lung cancer enigma that was proposed in 2004 by Adrianne Bendich of GlaxoSmithKline. Bendich suggested that superior lung function “could translate into deeper breathing of the carcinogens and other oxidants in smokers; that could result in a greater carcinogen burden in smokers supplemented with beta-carotene than those on placebo.”^3b

Does this mean that smokers should take beta-carotene supplements? The answer rests on weighing an increased risk of lung cancer against a decreased risk of many other serious diseases, such as emphysema, other cancers, cardiovascular disease, and immunity problems — diseases that are inhibited by beta-carotene consumption. One would have to quantify all these risks and calculate the net risk. Not an easy task, but it’s basically a choice between using beta-carotene to keep one’s lungs intact (and raising the risk of lung cancer), or opting for letting one’s lungs deterioriate (and increasing the risk of emphysema, other cancers, and various other ailments).

References

[1]  Beta-Carotene [review] PDR Health website

[2]  Dietary vitamin A and risk of cancer in the Western Electric study. Lancet. 1981 Nov 28;2(8257):1185-90

[3a]  From 1989 to 2001: what have we learned about the "biological actions of beta-carotene"? [abstract] J Nutr. 2004 Jan;134(1):225S-230S

[3b]  From 1989 to 2001: what have we learned about the "biological actions of beta-carotene"? [full text] J Nutr. 2004 Jan;134(1):225S-230S

[4]  Patrick L Beta-carotene: the controversy continues.

[5a]  The effect of vitamin E and beta carotene on the incidence of lung cancer and other cancers in male smokers. [abstract] N Engl J Med. 1994 Apr 14;330(15):1029-35

[5b]  The effect of vitamin E and beta carotene on the incidence of lung cancer and other cancers in male smokers. [full text] N Engl J Med. 1994 Apr 14;330(15):1029-35

[6a]  Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease. [abstract] N Engl J Med. 1996 May 2;334(18):1150-5

[6b]  Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease. [full text] N Engl J Med. 1996 May 2;334(18):1150-5

[7]  Beta-carotene could slow down lung aging NutraIngredients website

[8]  Serum carotenoids, vitamins A and E, and 8 year lung function decline in a general population. Thorax. 2006 Apr;61(4):320-6

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LifeLink carries beta-carotene in 25000 i.u. softgels.