Understanding human mortality through worms

It’s very bold to invent a new word. Its even more bold to invent a new word and add that as a keyword of your science article! That’s exactly what Ankita Bansala, Lihua Zhua, Kelvin Yena, and Heidi Tissenbaumam did in their paper¹ on which they question the value of the term “lifespan” and probe key assumptions using worms. Their newly invented term, gerospan, shows up about 34 times and, though they don’t say exactly where it comes from, it seems to be a mashup of the more common “lifespan” with the department of one of the authors (Gerontology, which means - literally - the study of old people).

The researchers made mutations in some worms that increased their lifespan² and compared them to wild-type worms by looking at a number of quantitative physiological parameters including heat stress resistance, oxidative stress resistance, and motility. They then divided the lifespan of the worms into two parts - a healthspan and a gerospan which are basically the “good” part of life and the “crappy” part of life, respectfully. The researchers defined it as:

Healthspan is defined as the period when the animal has greater than 50% of the maximal functional capacity of wild type.

Gerospan is defined as the period when the animal has less than 50% of the maximal functional capacity of wild type.

By looking at the physiological parameters they determined at which point in the worms’ lives the worm stopped being able to have 50% the maximaml functional capacity of that particular trait.

The researchers found that the worm mutants could live longer - up to twice as long as normal worms. Using these physiological parameters above to gauge well-being, though, the researchers showed that an increase in lifespan simply increases the gerospan (the crappy part of life) for every worm mutant. In other words, every worm that had mutations to live longer ended up just increasing the gerospan and not the healthspan.

Unfortunately most people obsess about how long they live, neglecting whether their longevity of life is also healthy and happy. That’s the distinction the authors are looking at here. Though this study was done on worms, the ideas easily carry over to human medical practices and emphasize the need to study whether healthcare practices increase our own healthspan or our gerospan.

Anyone who has to make a decision about how much money to invest in living longer - whether it be extreme (life support, cancer treatments) or minor (staying out of the sun for the rest of your life to avoid skin cancer). This study shows that we need to rethink the assumption that longer life is a better life, but rather longer healthier life is a better life.

This studies opens up a new avenue of research that has since been neglected - one that needs to now answer the question Quantity or Quality? The authors invented a new term, gerospan, that will help in this endeavor because it allows scientists to determine whether claims about longer lives are truly making a healthier, longer lives.

References

1. Bansal, Ankita, et al. “Uncoupling lifespan and healthspan in Caenorhabditis elegans longevity mutants.” Proceedings of the National Academy of Sciences 112.3 (2015): E277-E286.
2. Klass, Michael R. “A method for the isolation of longevity mutants in the nematode Caenorhabditis elegans and initial results.” Mechanisms of ageing and development 22.3 (1983): 279-286.