Smoking doubles dementia risk in late life

Heavy smoking during middle age can double the risk of Alzheimer's disease and dementia two decades later, researchers said on Monday.
Smoking already causes millions of deaths each year from cancer and heart disease.
"Our study suggests that heavy smoking in middle age increases the risk of both Alzheimer's disease and vascular dementia for men and women across different race groups," Rachel Whitmer, a research scientist with Kaiser Permanente in Oakland, California and colleagues wrote in the Archives of Internal Medicine.
They said smoking also causes cancer and heart disease. The new findings show it threatens public health in late life, when people are already more likely to develop dementia.
Whitmer's team analyzed data from 21,123 members of a health plan who took part in a survey when they were in their 50s and 60s.
About 25 percent of the group, 5,367 volunteers, were diagnosed with some form of dementia in the more than 20 years of follow up, including 1,136 people who were diagnosed with Alzheimer's disease.
Alzheimer's, the most common form of dementia, is a fatal brain disease in which people gradually lose their memories and their abilities to reason and care for themselves. It affects more than 26 million people globally.
People who smoked more than two packs of cigarettes a day had a higher risk of both Alzheimer's disease and vascular dementia.

"The increase in risk is not just for heavy smokers," Whitmer said in a telephone interview. "It's not if you smoke less you are in the clear, that is for sure."

She said compared with nonsmokers, those who smoked more than two packs a day had a 114 percent increased risk of dementia, a 157 percent increased risk of Alzheimer's disease and a 172 percent greater risk of vascular dementia.

Whitmer said it has been difficult to study the effects of smoking on brain health because heavy smokers often die from other conditions first.

"This is the first time someone has been able to look really over the long term," Whitmer said.

"We've known for some time that smoking is bad for your respective health," she said. "This really adds to our understanding that the brain is also susceptible.

The World Health Organization says 5 million people die every year from tobacco-related heart attacks, strokes and cancers. Another 430,000 adults die annually from breathing second-hand smoke.

A report last month said the worldwide costs of coping with dementia will reach $604 billion in 2010, more than one percent of global GDP output, and those costs will soar further as the number of sufferers triples by 2050.

It has been documented that smoking increases the risk of most diseases and mortality, but some studies have shown that smoking can reduce the chances of developing Parkinson's disease and other neurodegenerative diseases.

"The link between smoking and risk of Alzheimer's disease, the most common subtype of dementia, has been somewhat controversial, with some studies suggesting that smoking reduces the risk of cognitive impairment," the authors wrote in the report, posted online on Monday in the Archives of Internal Medicine, published by the Journal of the American Medical Association (JAMA).
Minna Rusanen from the University of Eastern Finland and Kuopio University Hospital in Kuopio, Finland, analyzed data with colleagues from 21,123 members of a healthcare system who participated in a survey between 1978 and 1985, when they were between the ages of 50 and 60.
The diagnosis of Alzheimer's and other forms of dementia were made between January 1994 and end in July 2008. The patients were on average 71.6 years old at the time.
Of those patients studied, 5,367 participants, or 25.4 percent, were diagnosed with dementia during an average follow-up period of 23 years, including 1,136 and 416 in Alzheimer's and vascular dementia.
Those of the patients who smoked more than two packs of cigarettes per day in their fifties had a very high risk of developing dementia and Alzheimer's in particular compared to non-smokers.
Race and sex were not factors in the study, the authors said.
Smoking is a known risk factor for stroke, and may help increase the risk of vascular dementia in a similar manner, the authors wrote.
The habit also contributes to oxidative stress and inflammation, believed to be important in the development of Alzheimer's disease.

Smoking may affect dementia development via vascular and neurodegenerative pathways, the authors write.

"Our study suggests that heavy smoking in middle age increases the risk of both Alzheimer's disease and vascular dementia for men and women across different race groups. The large detrimental impact that smoking already has on public health has the potential to become even greater as the population worldwide ages and dementia prevalence increases."
The authors said it is the first study that studies "the amount of midlife smoking on long-term risk of dementia and dementia subtypes in a large multiethnic cohort."
Smoking is blamed for several million deaths per year from causes such as heart disease and cancer, according to background information in the article.