Telomeres protect chromosome ends and help stabilize the genome. Throughout human life and in aging, telomeres often erode down, eventually causing cells to malfunction or die. The highly regulated cellular enzyme telomerase adds telomeric DNA to telomeres, and thereby can counteract telomere shortening to variable degrees. Telomere shortness can cause, and is frequently linked to, major chronic diseases that increase with aging, such as cardiovascular diseases, diabetes, and cancers. New research clarifies the concept that optimally regulated telomere maintenance processes, rather than simply greater telomere length, defines minimal overall disease risks throughout human life. Chronic psychological stress exacerbates telomere shortening. Current work aims to address which interventions optimize telomere preservation in ways protective of health.