Researchers here find an association between the amount of mitochondrial DNA (mtDNA) in tissues and the risk of frailty and mortality. The less mitochondrial DNA you have, the worse off you are likely to be, or so it seems. It is an interesting result, though at this point we can only speculate about how this relates to the role of mitochondrial DNA damage in aging. The many processes involved in mitochondrial dynamics are collectively exceedingly complex and the amount of mitochondrial DNA in cells has no direct relationship to its quality, yet both can impact health.
[Researchers] analyzed the amount of mtDNA in blood samples collected for two large, human studies that began in the late 1980s and tracked individuals' health outcomes for 10 to 20 years. 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. On average subjects who met the criteria for frailty had 9 percent 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 percent more likely to be frail than participants in the top one-fifth. "It makes intuitive sense that decreased mtDNA is associated with bad health outcomes. As we age, our energy reserves decrease, and we become more susceptible to all kinds of health problems and disease."
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 percent more likely to die of any cause during the study period than were those in the top one-fifth. They also found that women had an average of 21 percent more mtDNA than men. This could play a small role in why women live two to four years longer than men on average. The research team would like to take repeated blood samples from individuals over several years to learn if and by how much mtDNA levels decrease over time. What the investigators saw in the current study is that, averaged over the population, an increase of 10 years in age corresponded to 2.5 percent less mtDNA.