Shorter telomeres appear to be a bad thing, but their relationship to longevity is not straightforward: "Although telomere length (TL) is known to play a critical role in cellular senescence, the relationship of TL to aging and longevity in humans is not well understood. In a large biracial population-based cohort, we tested the hypotheses that elderly persons with shorter TL in peripheral white blood cells have poorer survival, shorter life span, and fewer years of healthy life (YHL). ... TL [was] not associated with overall survival or death from any specific underlying cause including infectious diseases, cancer, or cardiac and cerebrovascular diseases. TL, however, was positively associated with more YHL. Findings suggest that TL may not be a strong biomarker of survival in older individuals, but it may be an informative biomarker of healthy aging." Which suggests to me that telomere length is broadly associated with all sorts of poor health and age-related decline, but modern medicine is blunting the resulting hit to life expectancy. Questions of cause and effect remain, however: is telomere shortening merely a reflection of other age-related damage, or a fundamental damage-causing process itself?