The fatty acid composition of membrane lipids varies
systematically among species in a manner that is consistent with their
metabolic rate and longevity. Because the susceptibility of fatty acids
to peroxidation relates directly to their extent of unsaturation, it is
possible to calculate a peroxidation index (PI) for membranes
through characterization of their specific fatty acid composition.
Long-living mammals and birds have membrane lipids with a lower
PI than shorter-living species. Bird and mammal species with the
same maximum life span also have membrane lipids with essentially
the same PI. Exceptionally long-living mammals and birds usually
have membrane lipids high in monounsaturates, but low in
polyunsaturates, with the consequence that the PI of their membrane
lipids is as low as expected for their respective longevity. Longevity
variation within species (whether due to calorie-restriction, extended
longevity associated with specific strains, queen-worker differences
in honey bees or inherited longevity differences among humans) is
also associated with differences in membrane composition and PI.
Membrane composition is specific for each species and PI appears to
generally be resistant to dietary manipulation. It is postulated that
membrane fatty acid composition is an important influence on aging
and the determination of maximum life span.