Some mitochondrial DNA lineages are objectively better than others, as demonstrated by correlations with longevity in humans. Here is a correlation with dementia risk, which might be superficially explained by a greater ability to power fuel-hungry neurons, or greater resistance to mitochondrial damage over time: "Mitochondrial dysfunction is a prominent hallmark of Alzheimer's disease (AD). Mitochondrial DNA (mtDNA) damage may be a major cause of abnormal reactive oxidative species production in AD or increase neuronal susceptibility to oxidative injury during aging. The purpose of this study was to assess the influence of mtDNA sequence variation on clinically significant cognitive impairment and dementia risk in the population-based Health, Aging, and Body Composition (Health ABC) Study. We first investigated the role of common mtDNA haplogroups and individual variants on dementia risk and 8-year change on the Modified Mini-Mental State Examination (3MS) and Digit Symbol Substitution Test (DSST) among 1,631 participants of European genetic ancestry. Participants were free of dementia at baseline and incidence was determined in 273 cases from hospital and medication records over 10-12 follow-up years. Participants from haplogroup T had a statistically significant increased risk of developing dementia and haplogroup J participants experienced a statistically significant 8-year decline in 3MS, both compared with common haplogroup H. [Other variants were] associated with a significant decline in DSST score [or] 3MS score."