Living longer doesn't necessarily mean living better. That's the lesson from the tiny roundworm called C.elegans, long a workhorse in basic biology lab work. The research is in the Proceedings of the National Academy of Sciences. In the study, thousands of normal C. elegans competed against strains that live days or weeks longer than their brethren, because of factors like genetic mutations or very low-calorie diets.

But a battery of tests to see how all the older worms moved or responded to stress revealed some hard truths: increased life span did not usually come with a prolonged period of health and strength. Indeed, the "good times" for each of the worms was roughly the same, regardless of their overall life span. In other words, the longer-living worms spent a greater proportion of their lives in a diminished state—with less mobility and stress resistance.

Aging worms are not aging humans. But if the findings do extend to people, then life-extension efforts, such as calorie restriction, may not shake out to a better old age, just more years of frailty, with associated healthcare cost increases and quality of life decreases. The researchers suggest that it's time to start thinking about what they call "health span", and maximizing "healthspan", rather than just tacking on years of poor quality.