Every few years research on the effects of deuterium on life span in lower animals surfaces, by way of exposing them to heavy water, D2O rather than H2O. The presence of deuterium rather than hydrogen results in an uptake of deuterium atoms into biological molecules, subtly and slightly changing their behavior. Too much of that and you fall over dead - the mechanisms of life do not have a high tolerance for such tinkering, and heavy water is effectively toxic. At lower levels, however, species such as flies and nematodes live longer as a result of exposure to deuterium. A few articles and papers were published back in 2007-2009, which together give a fair grounding as to where the science stands:
Dr Shchepinov's theory is based on deuterium, a naturally-occurring isotope, or form of hydrogen, that strengthens the bonds in between and around the body's cells, making them less vulnerable to attack. He found that water enriched with deuterium, which is twice as heavy as normal hydrogen, extends the lifespan of worms by 10 per cent. And fruitflies fed the 'water of life' lived up to 30 per cent longer.
There is some skepticism and debate amongst various parties regarding the mechanisms by which deuterium uptake extends life span, but it's clear that exposure to heavy water at lower levels does in fact extend life in flies, worms, and so forth. Not too many people are working on this, so there is a lot of room for speculation and a lack of hard evidence that can rule out possibilities such as increased resistance to oxidative damage in important proteins. Given the evidence backing the membrane pacemaker theory of longevity, this is an attractive idea - there is plenty of support for the hypothesis that differences in the proteins that make up cell membranes are responsible for large differences in life span between various otherwise similar species. But robust evidence for the much smaller difference of a little extra deuterium substituted for hydrogen atoms - as opposed to completely different proteins - is lacking.
On this topic, I see that a new paper has arrived in the prepublication queue at Rejuvenation Research. It adds more data to the current thin stack on deuterium and fly life span:
We have investigated the effects of brief, non-specific deuteration of Drosophila melanogaster by including varying percentages of 2H (D) in the H2O used in the food mix consumed during initial development. Up to 22.5% D2O in H2O was administered, with the result that a low percentage of D2O in the water increased mean lifespan, while the highest percentage used (22.5%) reduced lifespan. After the one-time treatment period, adult flies were maintained ad libitum with food of normal isotopic distribution.
At low deuterium levels, where lifespan extension was observed, there was no observed change in fecundity. Dead flies were assayed for deuterium incorporation ... Isoleucine and leucine residues showed a small, linear dose-dependent incorporation of deuterium at non-exchangeable sites. Although high levels of D2O itself are toxic for other reasons, higher levels of deuterium incorporation, which can be achieved without toxicity by strategies that avoid direct use of D2O, are clearly worth exploring.
Hormesis is a possible (and disappointingly ordinary) explanation for this sort of result. Given the range of ways to make flies, worms, and rodents live longer by exposing them to adversity in early life, this almost seems like the first place to be looking. Perhaps lesser degrees of heavy water exposure, entirely separately from any deuterium uptake into proteins, have a hormetic effect, causing enough damage and disarray to spur repair mechanisms into greater efforts and leading to a net gain in life expectancy.
Well, either way, we shall hear more in future years. As the researchers point out above, you can conduct similar studies without the need for heavy water, and those should produce a more useful set of data.