Increased long-term risk of dementia in patients with carbon monoxide poisoning: A systematic review and meta-analysis of cohort studies

Abstract

Background It has long been known that carbon monoxide poisoning is associated with cognitive dysfunction but whether carbon monoxide poisoning is a risk factor for incident dementia is still inconclusive. Our objective was to assess whether carbon monoxide poisoning increases the incidence of dementia. Methods We conducted a systematic review and meta analysis of cohort studies examining the risk of dementia in people with carbon monoxide poisoning. We searched the Cochrane Library, PubMed, and EMBASE from inception to 31 March 2019. Two authors independently selected studies, assessed the quality of included studies, and extracted data. Any disagreement was resolved by discussion with a third author. Only cohort study with an enough follow-up period was included, which reported the association between carbon monoxide poisoning and incidence of dementia in adults. Exposure was carbon monoxide poisoning; primary outcomes were incident all-cause dementia, Alzheimer’s disease and cognitive disorder. Summary estimates were obtained using random effects meta-analysis. Results Thirty-three full texts were initially searched, but only three studies met our inclusion criteria, and they were comprised of 134,563 participants who were initially free of dementia. The follow-up period ranged from 9 to 12 years. We found that CO poisoning increased the risk of dementia incidence [adjusted hazard ratio 2.61, 95% confidence interval (CI) 1.56 to 4.36, P = 0.0003]. Subgroup analysis showed that the increased dementia risk was significant in males but not in females, and the highest risk was in young age group, followed by in middle age group, but not in the old one (P > 0.05). Conclusions This meta-analysis suggests that overall the evidence from prospective cohort studies supported a link between carbon monoxide exposure and an increased dementia risk, although all the included studies were limited to Taiwanese population. Further studies that provide data for different ethnic groups are needed to clarify whether a subgroup of patients with carbon monoxide exposure has an elevated risk of dementia.