How much impact does a colder temperature really have on lifespan?
Instead, it has revealed that genes determine the extent to which low temperature can influence an individual's lifespan.
The research is the work of scientists at the Marine Biological Laboratory (MBL) in Woods Hole, MA, which is an affiliate of the University of Chicago in Illinois.
The MBL team is investigating factors that affect aging using tiny aquatic animals called rotifers.
They chose rotifers because the microscopic organisms offer several advantages over other biological models such as fruit flies.
One such advantage is that they have more genes in common with humans. Another is that their bodies are transparent, so it is easier to observe their biology.
In addition, while their bodies only contain around 1,000 cells, rotifers possess a nervous system complete with brain, muscle tissue, and systems for reproduction and digestion.
There is now a report on the study in the journal Experimental Gerontology.
'Free radical theory of aging'
For decades, the free radical theory has been the "most popular concept in the area of aging." In fact, journals have published thousands of papers on it every year.
Scientists have used it, for example, to explain why many animal species live longer in colder climates.
The free radical theory maintains that animals age because of the buildup in cells of damage from metabolic byproducts called reactive oxidative species (ROS).
It also says that because temperature slows metabolic rate, it slows the release of ROS and so less cell damage accumulates over time.
First study author Dr. Kristin E. Gribble says that "there are people out there who believe, strongly, that if you take a cold shower every day it will extend your lifespan."
The MBL researchers write that they "tested the effect of low temperature on aging in 11 strains of Brachionus rotifers."
They note that if the free radical theory is correct, the increase in lifespan should be largely similar in all 11 strains.
Genetic variability matters
However, the results told a different story. The change in the median lifespan of each strain ranged from a decrease of 6 percent to an increase of 100 percent.
The team also observed "differences in maximum and relative lifespan extension and in mortality rate."
It also saw that in most strains, low temperature extended the "reproductive period and shortened the post-reproductive period, suggesting an extension of healthspan in most strains."
This would suggest that, depending on genetic makeup, colder temperatures can increase the proportion of lifespan that is spent in good health, even if it does not extend lifespan itself.
On the basis of these results, the researchers propose "that the mechanism of low temperature lifespan extension is an active genetic process."
"This means we really need to pay more attention to genetic variability in thinking about responses to aging therapies. That is going to be really important when we try to move some of these therapies into humans."
Dr. Kristin E. Gribble