Researchers have found that germ cells, which develop into eggs and sperm, drive sex-dependent differences in lifespan in vertebrates. Female and male germ cells increase and reduce lifespan, respectively. These effects are controlled via estrogen and growth factor hormones in females and vitamin D in males. Vitamin D supplementation extends lifespan in both males and females. The results clarify the link between reproduction and aging and show that vitamin D may improve longevity in vertebrates.