Predictor of Frailty & Death Revealed

Mitochondria are structures within cells often referred to as "power houses" because they generate most of cells' energy. Unlike other cell structures, they contain their own DNA -- separate from that enclosed in the nucleus -- in the form of two to 10 small, circular chromosomes that code for 37 genes necessary for mitochondrial function. There are 10 to thousands of mitochondria per cell, depending on a cell's energy needs.  A team from the Johns Hopkins University (Maryland, USA) previously revealed a link between genetic differences in mtDNA to increased frailty and reduced muscle strength in older individuals. In the current research, the team analyzed the amount of mtDNA in blood samples collected on 4,982 subjects enrolled in the Cardiovascular Health Study (1989-2006) and 11,509 participants in the Atherosclerosis Risk in Communities study (1987-2013). After calculating how much mtDNA each sample contained relative to the amount of nuclear DNA, the team looked at measures of frailty and health status gathered on the studies' participants over time. Subjects who met the criteria for frailty had 9% less mtDNA than nonfrail participants. And, when grouped by amount of mtDNA, white participants in the bottom one-fifth of the study population were 31% likely to be frail than participants in the top one-fifth.  The researchers also analyzed the age at which participants died. In one of the studies, high levels of mtDNA corresponded to a median of 2.1 extra years of life compared to those with the lowest levels of mtDNA.  Using data from both studies, the team found that those with mtDNA levels in the bottom one-fifth of the population were 47% more likely to die of any cause during the study period than were those in the top one-fifth.  Observing that: “Mitochondrial DNA (mtDNA) copy number is associated with age and sex,” the study authors conclude that: Lower mtDNA copy number is also associated with prevalent frailty. mtDNA copy number is a significant predictor of all-cause mortality in a multiethnic population.”