Familial aggregation of survival and late female reproduction

Abstract

Women giving birth at advanced reproductive ages in natural fertility conditions have been shown to have superior postmenopausal longevity. It is unknown whether improved survival is more likely among relatives of late-fertile women. This study compares survival past age 50 of men with and without a late-fertile sister in two populations: Utahns born in 1800-1869 identified from the Utah Population Database and Québec residents born in 1670-1750 identified from the Programme de recherche en démographie historique. Male survival was greater for those with, rather than without, a sister reproducing after age 45, particularly among men with at least three sisters (Utah rate ratio [RR] = .801, 95% CI = 0.687-0.940; Quebec RR = .786, 95% CI = 0.664-0.931). Survival of wives was unaffected by whether their husbands had a late-fertile sister, suggesting a weak influence of unmeasured socioenvironmental factors. These results support the hypothesis that late female fertility and slow somatic aging may be promoted by the same genetic variants.

Figure 1.

Mortality hazard rate ratios (HRRs) for brothers living to age 50 by age-at-last-birth of sisters who also survived to age 50 based on Cox proportional hazards models. HRR estimates are diamonds for Utah and squares for Quebec. Vertical bars represent HRR (95% confidence intervals) that adjust for familial clustering. See text for other variables controlled in the models. The comparison group comprises brothers whose sisters are all in the bottom 50th percentile. (A) Survival of men with sisters whose maximum age-at-last-birth was in the 50th–84th percentile of the female age-at-last-birth distribution. (B) Survival of men with a sister whose age at last birth is more than or equal to 85th percentile of the female age-at-last-birth distribution.