Heavy smoking in midlife increases an individual's risk of developing Alzheimer's disease by more than 157 percent, according to a new study sponsored by Kaiser Permanente. Researchers suspect the link could be explained by the increased inflammation that is present both in smokers and in individuals with Alzheimer’s disease, USA Today reported Oct. 25.

A review of records of more than 21,000 men and women found that compared with nonsmokers, those who smoked more than two packs of cigarettes a day had a more than 157 percent greater risk of developing Alzheimer's and a 172 percent greater risk of developing vascular dementia. Principal investigator Rachel Whitmer, Ph.D., a Kaiser Permanente research scientist, said a follow-up study will seek to determine whether quitting smoking might lower dementia risk.

The study followed subjects beginning in middle age for an average of 23 years. A total of 5,367 subjects were diagnosed with dementia in their later years, and 2,367 of these individuals were smokers. A total of 261 people in this group were classified as heavy smokers.

“This is another good reason not to smoke,” said William Thies, chief medical and scientific officer at the Alzheimer's Association.

Brenda Plassman, at Duke University Medical Center, said that the study showed no differences in dementia risk based on subjects' race.

The research was published online Oct. 25 in the Archives of Internal Medicine.