Why do some smokers live long beyond their life expectancy?

I’ve always been intrigued by people who tell me they’ve been smoking “since they were in the cradle” and are still alive at a ripe, old age. How does this happen when it’s well known that long-term smokers are at risk for developing cancer and heart disease, and their life expectancy is at least 10 years less than nonsmokers?

Researchers from the University of California in Los Angeles and the University of Southern California conducted a genome-wide association study comparing long-term smokers to people who smoked for shorter periods of time. These results were used to conduct a functional pathway analysis to identify single nucleotide polymorphisms (SNPs) that collectively related to smokers’ longevity.

They identified a set of 215 SNPs and used them to create a weighted polygenic risk score that, using an independent validation sample of nonsmokers (N = 6447), was found to be significantly associated with a 22% increase in the likelihood of being age 90—99 years (n = 253) and an over threefold increase in the likelihood of being a centenarian (n = 4), compared to being age 52–79 years (n = 4900).

The study identified a set of SNPs that together appear to be important for human aging, stress resistance, cancer, and longevity. In other words, these individuals have genetic variants that allowed them to have long-term exposure to a carcinogen without developing lung cancer.

Reference

Levine ME, Crimmins EM. A genetic network associated with stress resistance, longevity, and cancer in humans [published online September 9, 2015]. J Gerontol A Biol Sci Med Sci. doi: 10.1093/gerona/glv141.