The use of antioxidants to prevent various conditions associated with aging, like coronary heart disease and Alzheimer's, has been an on-again, off-again thing. Now the results of a very long study are available, and it may be that the length of treatment is the significant factor. Results are published in the Archives of Internal Medicine.

The Physicians Health Study II started in 1992. Over 4,000 men were assigned to take daily doses of 50 mg beta carotene plus low-dose aspirin or a placebo, every other day. An additional 2,000 men were added to the study between 1998 and 2001. Mental ability was tested in those over 65 at least once between 1998 and 2002.

The results of mental tests (cognitive ability) differed between those who had been in the study for an average of 18 years and those who'd been studied for 1 year. Short-term use of beta carotene provided no cognitive benefit, but in those with long-term use (an average 18 years) cognitive function was approximately that of men one year younger. In other words, taking beta carotene is by no means a 'short fix', but it appears to have benefits in the long term.

Interested users should remember that beta carotene is not without risk. In male smokers, supplements increase the lung cancer mortality rate. Nobody said life was easy.