Monday, January 14, 2013

Lifestyle Factors and Risk of Alzheimer's Dementia

The number of individuals suffering from Alzheimer's disease is rapidly increasing throughout the developed world.

A significant portion of this increase is explained by demographic trends as the Baby Boomer generation progresses through the high-risk age categories for Alzheimer's and other dementia.

It is important to understand potentially modifiable lifestyle risk factors that may stimulate a valid public health prevention program.

An important recent study examined lifestyle factors and risk for dementia among a cohort of Japanese American men.  

Gelber and colleagues followed a cohort of 3468 men over a period of 25 years.  The study focussed on the emergence of dementia including both Alzheimer's disease and vascular dementia.

The key components of the study design in this study included:

  • Cohort characteristics: Men of Japanese ancestry born between 1900 through 1919 living in Oahu, Hawaii
  • Dementia diagnosis: The cohort received regular neuropsychological screening with cognitive deficits prompting neurologist referral.  The study neurologist and two physicians made decisions about a diagnosis of Alzheimer's disease or vascular dementia using clinical information, neuropsychological testing, blood tests and brain imaging (CT or MRI) results. 
  • Modifiable risk factor variables: BMI category, smoking status, physical activity level, dietary intake and alcohol consumption.  A global lifestyle low-risk group was identified that demonstrated the presence of a low risk on all four modifiable risk factors: BMI less than 22.6, never smoking, 3 or more hours per week of physical activity and high dietary score (more vegetable/fruit intake and moderate alcohol intake).

A total of 223 cases of dementia were identified during the follow up period.  The majority were assigned a diagnosis of Alzheimer's dementia (n=117), with vascular dementia a close second in frequency (n=78).  Twenty eight cases were given another cause for dementia.

High BMI, smoking and low physical activity all increased risk for overall dementia diagnosis with the following estimates for odds ratio of those with risk factor compared to those without:

  • BMI: Odds ratio= 1.87
  • Smoking: Odds ratio= 1.48
  • Low physical activity: Odds ratio= 1.59

Diet score did not show a statistically significant association with overall dementia risk.

However, when specific type of dementia was examined, none of the individual lifestyle factors proved to be statistically associated with Alzheimer's disease risk.  BMI, smoking status and low physical activity were individually linked to increased risk for vascular dementia at odds ratios estimated at high levels than in the overall dementia group.

Men positive for all four lifestyle factors showed a 64% reduction in dementia risk, but this was primarily in reduction of risk for vascular dementia.

Finding no association between lifestyle factors and risk for Alzheimer's disease is somewhat discouraging.  It suggests that genetic factors, i.e. APOE gene status, may be resistant to the moderating effects of lifestyle changes.  

However, the study supports promotion of a healthy lifestyle approach in mid-life to reduce risk of vascular dementia.  Adopting all four factors in a healthy lifestyle promotes a significantly reduced risk of later dementia diagnosis.

Readers with a more detailed interest in the study can access the free full text article by clicking on the PMID link below.

Photo of burrowing owl from the author's files. 

Gelber RP, Petrovitch H, Masaki KH, Abbott RD, Ross GW, Launer LJ, & White LR (2012). Lifestyle and the risk of dementia in Japanese-american men. Journal of the American Geriatrics Society, 60 (1), 118-23 PMID: 22211390

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