Smoking in Middle Age Increases Dementia Risk

December 1st, 2010 | Sources: Archives Int. Medicine, Wall Street Journal

Most people know that cigarette smoking causes lung cancer and cardiovascular disease. Now, as if anyone needed another reason to kick the habit, a new study has shown that heavy smoking in middle-age is associated with an increased risk of Alzheimer’s disease and other forms of dementia as well.

To reach these conclusions, Minna Rusanen, Rachel Whitmer and colleagues at Kaiser Permanente identified 21,000 patients that had completed a cigarette smoking survey between 1978 and 1985, and then tracked down diagnoses that had been entered into their medical records between 1994 and 2008.

It turned out that nearly 5,400 people (25%) from the original cohort were diagnosed with dementia, including 1,100 people that developed Alzheimer’s disease and another 400 that developed vascular dementia. After adjusting for a host of possibly confounding factors, Rusanen’s group found that people who reported smoking at least 2 packs of cigarettes per day on that initial survey were 2.15 times more likely than non-smokers to develop dementia from all causes, 2.5 times more likely to develop Alzheimer’s disease, and 2.7 times more likely to develop vascular dementia during follow-up.

The deleterious impact of smoking grew with increasing cigarette consumption. Thus, people who smoked “only” 1-2 packs per day had 1.4 times the risk of all-cause dementia. And former smokers—those who said they’d quit at the time of the initial survey—were not at increased risk for dementia.

“It’s a pretty clear picture that heavy smoking … elevates your risk of dementia,” said Whitmer, who works at Kaiser Permanente’s research division in Oakland. “If you are a heavy smoker and you’re lucky enough to make it to old age, you’re not in the clear. You’re still at risk for dementia.”

The study confirms the results of recent clinical trials on the relationship between cigarette consumption and Alzheimer’s disease. An interesting historical note is that older studies had actually suggested that smoking reduced the risk of cognitive impairment and dementia in elderly folks. Most scientists have discounted these older studies because many of the heavy smokers in those studies ended up dying before they had a chance to develop Alzheimer’s disease; that’s a phenomenon which could have biased the results.

The write-up of the current study appears in the Archives of Internal Medicine.


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