Why Healthspan is more Important than Longevity

In their defensive state, mitochondria produce reactive oxygen species (ROS), which act both as byproducts and regulators of metabolism. In small amounts, ROS promote adaptation and build resilience, but in excess they damage proteins, lipids and DNA.  

Normally, ROS generation is balanced by antioxidant defenses, yet with age, mitochondrial quality control mechanisms against ROS-induced damage weaken, and the scale tips in favor of ROS production.  

This imbalance can open channels known as mitochondrial permeability transition pores. Brief pore openings are part of normal stress signaling; however, chronic or unregulated openings cause mitochondrial collapse and cell death. ROS can trigger these pores, and the resulting pore opening further amplifies ROS production, leading to a self-reinforcing loop that prevents the cell from returning to metabolic balance.  

Despite this, oxidative stress alone cannot explain aging. Studies show that increased ROS does not always shorten lifespan and can even promote longevity under certain conditions. This suggests that mitochondria influence aging through more than just oxidative damage caused by ROS.  

Aging and decreased lifespan are associated not only with ROS production and increased mitochondrial DNA damage but also with changes in fatty acid composition of mitochondrial membranes. This composition influences how easily membrane lipids become oxidized and can therefore act as a determinant of aging.  

For example, species with very low levels of membrane polyunsaturated fatty acids, such as lizards, tend to live longer. This observation forms the basis of the membrane pacemaker hypothesis of metabolism, which proposes that higher levels of polyunsaturated fatty acids enhance metabolic rate but at the cost of increased susceptibility to oxidative damage.  

Likewise, impaired synthesis of cardiolipin, a phospholipid found almost exclusively in mitochondrial membranes, has been linked to reduced longevity. In contrast, plasmenyl lipids, which are more abundant in long-lived species, may act as natural membrane antioxidants that help balance oxidative stress.  

Because mitochondrial DNA is about ten times more vulnerable to mutation than nuclear DNA, mitochondria gradually lose their flexibility to shift between states with aging.  

Aging is frequently associated with a shift in mitochondrial dynamics, where there’s a loss of ability to divide, leading to abnormally enlarged mitochondria. Meanwhile, the electron transport chain, the cell’s main energy system, slows down with aging, leading to reduced energy production and more ROS generation.