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Cognitive function, but not education level, associated with mortality in hemodialysis
Researchers of a published study found that while cognitive impairment was associated with increased mortality for patients on hemodialysis, education level did not appear to have an impact.
“As many as 60% to 90% of patients with end-stage kidney disease receiving dialysis have some level of cognitive impairment,” Anita van Zwieten, MPH, of the University of Sydney, and colleagues wrote. “Investigation of the independent and interactive associations of education with mortality is needed because education and cognitive function are closely intertwined. Higher levels of education are associated with lower risks for cognitive impairment and mortality in the general population. Studies of education-mortality associations in dialysis patients have produced mixed findings, including protective and nonsignificant associations.”
Researchers conducted a prospective cohort study, Cognitive Impairment in Adults with ESKD Treated with Hemodialysis (Cognitive-HD), that included 676 adults from 20 Italian dialysis clinics (median age, 70.9 years; 38.8% were women). Participants were classified by education level as primary or lower, lower secondary and upper secondary or higher.
Researchers assessed cognitive function using a neuropsychological battery of 10 tests, considering the domains of learning and memory, complex attention, executive function, language and perceptual-motor function. Cognitive impairment in at least one domain was present in 79.4% of the study population.
Researchers of a published study found that while cognitive impairment was associated with increased mortality for patients on hemodialysis, education level did not appear to have an impact.
Patients were followed for a mean of 3.3 years. During this time, 206 deaths occurred: 5.1 deaths per 100 person-years in participants with no impairment vs. 12.6 deaths in those with at least one impaired cognitive domain.
Researchers found a dose-dependent association between the number of cognitive domains impaired and mortality, with 8.7 deaths per 100 person-years for one domain, 10.8 deaths per 100 person-years for two domains and 14.6 deaths per 100 person-years for three to five domains. No association was observed between education and mortality. Compared with primary or lower education, adjusted hazard ratios were 0.79 and 1.13 for lower secondary and upper secondary or higher, respectively.
The interaction between cognitive impairment and education was also not significant.
Regarding the association between cognitive impairment and premature death, researchers pointed out that comorbid conditions may have had confounding effects (eg, vascular disease as it is prevalent in patients with ESKD and associated with cognitive impairment).
Further, “Mechanisms that underlie associations between cognitive impairment and mortality are likely complex and multifactorial and at present are largely unclear,” they wrote. “Because the analysis did not differentiate between milder impairment and dementia, our findings reflect mortality associations across the spectrum of cognitive impairment ... Underlying mechanisms should be investigated to inform interventions. Future analyses of the Cognitive-HD study will [also] consider the association between cognitive impairment and functional impairment.”
Katharine L. Cheung MD, PhD, and Michael A. LaMantia, MD, MPH, both of the University of Vermont, suggested the study was limited because cognition was assessed during dialysis.
“Recent data demonstrate that dialysis induces an acute decline in cerebral blood flow and is associated with ultrafiltration rates and volume as well as temperature,” they wrote. “Conducting cognitive testing during hemodialysis may be highlighting flow-sensitive vascular lesions.”
They further noted that data related to the impact of educational attainment on the association between cognition and mortality was mixed, arguing that education may be linked to higher income and better access to health care which could mitigate the relationship between cognitive impairment and mortality. From another perspective, they suggested education may protect against cognitive impairment by shaping neural development.
“That education was not associated with mortality in this study does not rule it out as a potentially important factor,” they concluded. “As the authors point out, this may have been due to characteristics of this cohort (low levels of education or small education inequalities in mortality Italy) or may have been a chance finding.” – by Melissa J. Webb
Disclosures: van Zwieten reports no relevant financial disclosures. Please see the study for all other authors’ relevant financial disclosures.