New Study Finds Heavy Smoking in Midlife Increases Risks of Alzheimer's Disease and Vascular Dementia Later in Life by More than 100 Percent

A new study published in the February 28, 2011 issue of the Archives of Internal Medicine has found that heavy smoking in midlife may increase the risks of  getting Alzheimer Disease or Vascular Dementia later in life by more than 100%.

The study was conducted by scientists associated with the University of Eastern Finland, Kuopio University Hospital, Kuopio, Finland, the Karolinska Aging Research Center in Stockholm, Sweden, and Kaiser Permanente Division of Research in Oakland, California.

The purpose of the study was to measure, in a large, diverse study population, to what extent amount of smoking in middle age correlates with higher risk of dementia, including Alzheimer Disease as well as Vascular Dementia,  several decades later.   It has long been known that smoking is a risk factor for several life-threatening diseases, but its long-term affect on possible development of dementia was previously not clear. The study authors state that to their knowledge, “this is the first study to investigate the long-term association between the amount of smoking in midlife and the risk of dementia [Alzheimer's Disease and Vascular Dementia] later in life in a large, multiethnic cohort.” Previous studies had measured only an association between smoking and short-term risk of dementia.

In the study, researchers analyzed data collected from a multi-ethnic group of 21,123 patients in the Kaiser Permanente Medical Care Program in San Francisco and Oakland, California, who participated in a survey given as part of routine medical care between 1978 and 1985.   The survey collected a large amount of data on the subjects’ health habits, including the extent to which they smoked, as well as medical information about their height, weight, body mass index (BMI), blood pressure, glucose levels, incidence of stroke and cardiovascular problems, and other data. The study participants had a mean age of 58 years at the time of this baseline survey.

In follow up, between 1994 and 2008, a total of 5,367 (25.4%) of the study subjects, were diagnosed by neurologists, neuropsychologists or internal medicine physicians as having dementia. Of these, 1,136 cases of Azheimers Dementia and 416 cases of Vascular Dementia were confirmed during an average follow-up period of 23 years.

The researchers analyzed the data to determine whether extent of smoking in middle age correlated with dementia in later life. Results were adjusted to control for the potential effects of other factors, including age, sex, education, race, marital status, hypertension, hyperlipidemia, body mass index, diabetes, heart disease, stroke, and alcohol use.

The study results found that, compared to study subjects who did not smoke, those who smoked more than 2 packs a day at midlife had a greater than 100% increase in risk of both Alzheimer’s Disease and Vascular Dementia more than two decades later.

The association between smoking and dementia, including Vascular Dementia, remained significant even after controlling for the other factors, including other vascular problems and stroke. Thus, the researchers concluded, “smoking seems to also have some independent effect on VaD [Vascular Dementia], beyond acceleration of cerebro-vascular disease.” They suggested that further study is needed to isolate the exact mechanisms through smoking makes one susceptible to Alzheimer’s Disease. But, the authors observed, “It is well recognized that smoking augments oxidative stress and inflammation, which are also believed to be important pathophysiologic mechanisms in AD [Alzheimers Dementia].”

These results suggest that the brain may suffer long-term consequences as a result of heavy smoking in midlife. The study did not collect smoking data after midlife, so the authors were not able to evaluate whether those who stopped smoking after midlife were at less risk of dementia than those who continued smoking.

The authors of the study included Minna Rusanen, MD and Miia Kivipelto, MD, PhD of the University of Eastern Finland and Kuopio University Hospital, with Dr. Kivipelto also being affiliated with the Karolinksa Aging Research Center, Stockholm, Sweden; and Charles P. Quesenberry Jr, PhD; Jufen Zhou, MS; Rachel A. Whitmer, of Kaiser Permanente Division of Research, Oakland, California.

An abstract and the full text of the study are available from the Archives of Internal Medicine » Archives of Internal Medicine — Heavy Smoking in Midlife and Long-term Risk of Alzheimer Disease and Vascular Dementia, February 28, 2011.


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