Carrots and Cancer

A study conducted on 30,000 Finnish male smokers from 1985 to 1993 finds that smokers who took beta-cartoene supplements between 5 and 8 years had an 18% higher incidence of lung cancer than those taking a placebo. In 2004, another study involving 18,000 mixed gender participants finds that those given a beta carotene and retinyl palmitate supplement had a 28% increased incidence of lung cancer. Although this study concludes that primarily females are impacted by increased chance of lung cancer.

A 1999 University of Texas study tries to explain this paradox of beta carotene, a substance found in Vitamin A and thought to prevent cancer in non smokers, actually increasing the chance of lung cancer in smokers. The researchers observe rats fed large doses of beta carotene to have high levels of the enzyme CYP in their lungs. They hypothesize that CYP activates polycyclic aromatic hydrocarbons (PAH) found in tobacco smoke and causes cancer.

A slightly contradictory study of 22,000 American Doctors, of which 11% were smokers, showed that taking beta carotene supplements for 12 years provided no benefit or harm. The first part of the Harvard study concluded in 1995.

There is no evidence to suggest that smokers should cut down on foods that contain high levels of beta carotene. It may be that a component of these foods other than beta carotene helps to protect against cancer. Or, it may be that the whole food is better than a supplement.