Smoking raises your risk of developing dementia or Alzheimer's disease by 50 percent, according to researchers who tracked thousands of smokers and nonsmokers over age 55 for a period of seven years.

The authors found that smoking did not increase the risk of Alzheimer's for people who carried the gene for the disease, but did increase the risk for those who did not have the Alzheimer's gene.

HealthDay News reported Sept. 4 that study author Monique Breteler of Erasmus Medical Center noted, "Smoking increases the risk of cerebrovascular disease, which is also tied to dementia. Another mechanism could be through oxidative stress, which can damage cells in the blood vessels and lead to hardening of the arteries. Smokers experience greater oxidative stress than nonsmokers, and increased oxidative stress is also seen in Alzheimer's disease."

The study was published in the Sept. 4, 2007 issue of the journal Neurology.