There are several studies, with beta-carotene supplements, which are pre-stages of vitamin A. Vitamin A is found in two forms: as retinol in foods from animal sources, and as carotenoids in foods from plant sources, beta carotene being the most common carotenoid. Beta carotene can be converted to retinol in the body; 6mg of beta carotene is equivalent to 1mg of retinol. The total vitamin A content of the diet (from both animal and plant sources) is normally expressed as retinol equivalents.

The evidence on benefits and adverse effects of taking beta-carotene supplements is contradictory, and the potential health risks are not well understood. In several studies, beta-carotene supplements have been shown to have adverse effects on smokers, particularly increasing the risk of lung cancer. Another study designed to study beta-carotene for the prevention of recurrent colon polyps finds substantial benefit in people who neither smoke nor drink. In those who neither drank or smoked, there were non-significant increases in recurrence of new polyps. But in those who drank and smoked, there was a significant 207 percent increase in polyps.

The most recent analysis of a large study on smokers treated with vitamin E or beta-carotene generally failed to find any benefit of either supplement on the incidence of pneumonia among more than 29,000 men in Finland who took 20 mg of vitamin E or 50 mg of beta-carotene.

As for B vitamins, some people claim that deficiencies in B vitamins weaken the immune system and make the body vulnerable to cancer. They recommend high doses of B vitamins as a treatment for people with cancer. However, current scientific evidence has not found any effect of B vitamin supplements on the growth and spread of cancer. Many scientific studies in progress, are studying the relationships between vitamin intake and risk of developing certain cancers. At this time, taking beta-carotene, vit A or B vitamins supplements is not recommended for cancer treatment, in particularly for smokers. However, there are many studies that consistently show consuming fruit and vegetable sources of beta-carotene is associated with less cancer and better health. A well balanced diet rich in fruits and vegetables will contain enough Vitamin A, beta- carotene and B vitamins to promote health and at the same time not too much to have any adverse side effects.

The best advice for smokers who want to reduce their risk of lung cancer is still the most direct: stop smoking.

See also:

• /gb/heal/mg03.htm
• http://healthlink.mcw.edu/article/980793489.html