How long you live may depend much more on your genes than scientists thought

"Three decades ago a famous study of Danish twins found that our genes only moderately influence how long we're likely to live. Longevity, the authors estimated, was about 25 percent heritable, meaning the remaining three quarters was determined by environmental factors and lifestyle choices, such as diet and exercise. Most subsequent studies found heritability to be somewhere in the 20 to 25 percent range, and 25 percent is now widely accepted."

"But a new study more than doubles it, suggesting lifespan may be more genetically fixed than we thought. The study, which was published today in Science, arrives at this dramatic increase by reframing how scientists think about longevity. Rather than lumping all deaths together, the researchers distinguish between two kinds: intrinsic mortality comes from built-in biological aging processes and genetic mutations, whereas extrinsic mortality comes from outside causes, such as accidents and infection."

"To sort out the effects of intrinsic versus extrinsic deaths on longevity heritability, he and his colleagues ran computer simulations of human mortality, calibrated using data from those previous twin studies. When they dialed extrinsic mortality down to zero, leaving only deaths caused by intrinsic aging processes, lifespan heritability roughly doubled. Surprised, the team performed a sanity checkthe researchers calculated heritability in the traditional way for twins born between 1900 and 1935, an era when rapid medical advances steadily curtailed premature death."

Previous analyses estimated lifespan heritability at about 25 percent, attributing the remaining variance to environment and lifestyle. Reframing longevity by separating intrinsic mortality (biological aging and genetic mutations) from extrinsic mortality (accidents, infections, other external causes) produces a markedly higher genetic estimate. Computer simulations calibrated to twin-study data show that eliminating extrinsic mortality roughly doubles lifespan heritability. Historical twin cohorts born between 1900 and 1935 experienced declining extrinsic mortality alongside rising heritability, consistent with the simulation results. The distinction between intrinsic and extrinsic deaths therefore yields a stronger, more intrinsic genetic influence on lifespan.

Read at www.scientificamerican.com