SEATTLE, WASHINGTON. Senile dementia is a growing problem in both the developed and developing world. It is estimated that there are currently 30 million people with dementia worldwide with 4.6 million new cases being diagnosed annually. The number of people with dementia in the USA in the year 2002 was estimated at 3.4 million with 2.4 million of these individuals having Alzheimer's disease (AD). The estimated costs associated with AD (in the USA) are $172 billion each year. This is clearly a very serious problem!

About 20% of AD cases are associated with genetic mutations, but many other risk factors have been implicated. Among them:

• Advanced age
• Oxidative stress, vitamin deficiency, poor diet
• Low antioxidant levels
• Atherosclerosis and cardiovascular disease
• Diabetes
• Elevated homocysteine level
• Vitamin B12 and folate deficiency
• Low intake of omega-3 fatty acids (fish oil)
• Hypertension
• Exposure to pesticides and herbicide

Now researchers at the University of Washington report an association between dementia, including AD, and atrial fibrillation (AF). Their study included 3045 participants in the Adult Changes in Thought (ACT) study who were without dementia or prior stroke at enrolment beginning in 1994. The median age at study entry was 74 years, 60% of participants were women, and 38% had completed college. Twenty-two percent had coronary heart disease or heart failure, 32% were being treated for hypertension, 26% were obese, and 9% had diabetes at baseline. None of the participants had dementia or AD when enrolled, but 132 (4.3%) had documented AF at baseline. These patients were more likely to have cardiovascular risk factors and diseases than were those without AF at baseline.

During an average (mean) follow-up of 6.8 years, an additional 370 participants (12%) were diagnosed with AF and 572 (18.8%) developed dementia, including 449 (14.7%) with possible or probably AD. The incidence (annual rate of diagnosis) of AD in participants with AF was 4.8% vs. 2.5% in those without AF. Corresponding numbers for AD were 3.8% and 2.0%.

After adjusting for gender, education level, hypertension, diabetes, coronary heart disease, heart failure, and history of stroke or TIA, the researchers conclude that AF is associated with a 38% relative increase in the risk of all-cause dementia and a relative increase in the risk of AD of 50%. In absolute terms, this corresponds to about a 1%/year increase in the risk of developing dementia associated with AF.

The researchers speculate that the observed association may be due to decreased blood flow to the brain during AF, or to silent mini-strokes. They also point out that AF and dementia share underlying risk factors such as inflammation and cardiovascular disease. However, they admit that the prevalence of heart disease in the study population was based on self-reporting, which may be inaccurate. Also, information about valvular heart disease and echocardiographic findings such as left atrial enlargement and impaired systolic function, which are associated with development of AF, was not available.

Dublin, S, Larson, EB, et al. Atrial fibrillation and risk of dementia. Journal of the American Geriatrics Society, Vol. 59, August 2011, pp. 1369-75

Editor's comment: This study concludes that AF is associated with an approximately 1% per year absolute increase in the risk of developing dementia, mostly Alzheimer's disease among a group of elderly participants (average age at enrolment was 74 years) in the ACT study. Inasmuch as all participants were over the age of 65 years at time of enrolment, the results of the study cannot be extrapolated to a younger group of otherwise healthy afibbers. Nevertheless, taking precautions against developing dementia or AD would obviously be prudent. For more on this see Alzheimer's Disease: There is Hope! and Prevention of Alzheimer's Disease