Cold Makes Animals Live Much Longer. But Why?

Cold Makes Animals Live Much Longer. But Why?
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A fascinating trend roughly holds across all bounds of life: Whether plant, animal, fungus, or bacterium, the larger an organism is, the longer it lives. True, there are notable exceptions. Antarctic sponges -- odd-looking multicellular animals -- are capable of living thousands of years! Compare that to vastly larger bowhead whales, the longest-living mammals. They weigh around 200,000 pounds, yet only manage 211 years at best.

What then is the sponges' life-prolonging secret? Obviously, a sponge is not a whale, so a host of factors could be at play, but let's focus on an obvious difference: internal temperature. Antarctic sponges and bowhead whales inhabit similarly cold regions of the Earth, the Antarctic and Arctic oceans, respectively. Yet the sponges maintain a much colder internal temperature than the whales. This difference has not escaped the learned gaze of biologists, who've noticed an intriguing pattern. From poikilotherms -- organisms with varying internal temperatures -- to homeotherms -- organisms with stable internal temperatures -- being colder is linked to a longer life.

The trend is best demonstrated by comparing similar organisms. For example, different species of sponges inhabiting tropical or temperate zones have shorter lifespans than their counterparts living in more frigid waters. In the laboratory, fruit flies live about twice as long at 21 °C versus 27 °C. C. elegans worms survive 75% longer when 5 °C cooler. Many species of fish live between 14% and 75% longer at colder temperatures. Even mice that had their core body temperatures reduced by just 0.3 °C lived longer, to the tune of 12% for males and 20% for females.

These are all fascinating results, but don't go freezing yourself with the hope of tacking a few extra years onto your life. If body temperature is reduced too much, most organisms will suffer hypothermia, which doesn't foster longevity in the slightest -- it can result in death. The graphs below -- representing poikilotherms on top and homeotherms on bottom -- make that fact very plain.

Why does cold tend to make organisms live longer? The answer is still very much up for debate. One explanation, the "rate of living" hypothesis, suggests that lower temperature promotes longevity by slightly slowing metabolism and reducing damage resulting from the by-products of metabolism. While intuitive, this is nowhere close to being proven. In fact, it suffered a big setback in 2007 when a large review found no link between metabolism and longevity in mammals or birds.

In a recently published review, researchers from the Institute of Integrative Biology at University of Liverpool offered a more nuanced explanation. They suggest that cold prompts changes in activity from hormone-releasing neuroendocrine cells, and that these changes in turn impact aging and longevity. If that seems like a vague explanation, that's because it is. Simply put, biologists are still stumped on why cold boosts longevity, but more specific answers could come from a familiar source: naked mole rats.

Already studied for their incredible ability to resist cancer, these small rodents, which weigh just 30 grams, live to an astounding 30 years. Similarly sized mice survive no longer than three years. The average lifespan for rodents is around nine. Notably, mole rats have an internal temperature that's roughly 3-5 °C cooler than other rodents. The reviewers suggest this may be a factor, and that it merits study.

If scientists can uncover the mechanism behind cold's life-extending powers, we just might be able to harness it for the benefit of mankind, no refrigeration required.

Source: Keil G, Cummings E, de Magalhães JP. "Being cool: how body temperature influences ageing and longevity." Biogerontology. April 2015. DOI: 10.1007/s10522-015-9571-2

(Top Image: AP)

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