Add another notch to the evidence that an unhealthy heart can harm the brain. In the September 21 JAMA Neurology, researchers led by M. Arfan Ikram of Erasmus Medical Center in Rotterdam, the Netherlands, report that having atrial fibrillation, a common cardiovascular disease in older adults, was associated with an elevated risk of developing dementia over the next 20 years. The link was particularly strong for middle-aged participants, fueling a trend in epidemiology that cardiovascular health in midlife influences brain health in old age. “This highlights the fact that prevention needs to start years or decades before people develop cognitive symptoms,” co-author Frank Wolters told Alzforum. It is not yet clear, however, what type of treatment for this heart condition would most lower dementia risk.
“Their study clearly adds to the growing body of evidence that atrial fibrillation is a significant risk factor for dementia,” Jared Bunch at the Intermountain Medical Center Heart Institute, Murray, Utah, wrote to Alzforum.
Atrial fibrillation is an abnormal heart rhythm in which the upper chambers flutter irregularly, reducing blood flow. The heart can be coaxed back into normal rhythm with drugs or shocked with electricity, but the condition often recurs and persists. In people with the disease, the heart’s ineffective pumping can cause blood to clot, raising the risk of stroke. Thus, patients are often treated with anticoagulants. Notably, even tiny strokes or clotted matter in the blood can precipitate cognitive decline and dementia (see Jan 2008 news; Feb 2012 news; Dec 2012 news).
The connection between atrial fibrillation and stroke suggested to many researchers that the condition might also be a risk factor for dementia, but previous studies examining this have yielded mixed results. Some papers reported a link with Alzheimer’s disease, as well as vascular dementia, especially in people under 70 (Bunch et al., 2010; Dublin et al., 2011; Marzona et al., 2012). Other studies, mostly in people over 75, found no association (see Rastas et al., 2007; Peters et al., 2009; Marengoni et al., 2011). An early study in the Rotterdam cohort supported a link, but because participants were not followed over time, the researchers could not infer that the cardiac condition caused cognitive decline (see Ott et al., 1997).
To parse this out, first author Renée de Bruijn followed 6,514 cognitively normal participants in the Rotterdam Study who were 55 or older at baseline. About 5 percent had an initial diagnosis of atrial fibrillation, and another 12 percent developed the condition during the 20 years of the study. Overall, about 15 percent of the population developed dementia. Having atrial fibrillation increased the risk by about one-third, regardless of whether people also had a stroke.
However, it turned out that the association was driven by the younger members of the cohort. Among people under the population’s median age of 67, having atrial fibrillation nearly doubled dementia risk. Moreover, among this group, the longer a person had this heart problem, the higher their dementia risk rose. Those who had an atrial fibrillation diagnosis for more than 12 years tripled their risk of dementia. By contrast, among the older participants, atrial fibrillation did not significantly bump up risk, and there was no relationship with the length of time they had the condition.
Atrial fibrillation may be a stronger risk factor in younger people because they have more years to accumulate brain damage, Wolters suggested. Other recent studies have reported that cardiac and metabolic health in middle age—but not old age—influence later cognitive decline (see Jul 2014 news; Aug 2014 news; Sep 2015 news). Meta-analyses of these risk factors also support a midlife connection (see AlzRisk blood pressure and obesity analyses).
Does atrial fibrillation predispose to vascular dementia, or to AD specifically? In this study, 80 percent of the dementia cases were clinically diagnosed as Alzheimer’s according to older National Institute of Neurological and Communicative Disorders and Stroke—Alzheimer’s Disease and Related Disorders Association criteria (McKhann et al., 1984), but most were not confirmed by autopsy or amyloid imaging.
The finding hints that atrial fibrillation could be a risk factor for AD, though the mechanism remains a mystery. Dementia risk occurred independently of stroke in this cohort, but the authors noted that mini-strokes may have gone undetected and could have hastened cognitive decline. Chronic atrial fibrillation also could have lowered blood flow to the brain. Several previous studies have tied vascular health to amyloid deposition (see May 2013 news; Feb 2014 news; Apr 2014 news).
Could optimal treatment of atrial fibrillation prevent dementia? The authors could not address that because they had no data on how often or for how long participants had active fluttering of the heart, nor what treatments they took. “Future studies should examine the impact of different types of treatment for atrial fibrillation and whether they reduce the risk of cognitive decline. That will be vital for prevention,” Wolters said.—Madolyn Bowman Rogers
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- de Bruijn RF, Heeringa J, Wolters FJ, Franco OH, Stricker BH, Hofman A, Koudstaal PJ, Ikram MA. Association Between Atrial Fibrillation and Dementia in the General Population. JAMA Neurol. 2015 Nov;72(11):1288-94. PubMed.