Of Mice and Monkeys and Men
Sorry for yet another absence. We were finishing the second trial this month. Whatever happened to vacation letters?
Anyway, we were looking for something to blog about and came across In Re: Chantix (Varenicline) Products Liability Litigation. Among a number of other justifications for its rulings on motions to exclude plaintiffs' experts you'll find one in which the court relies on the assumption that "[i]n qualitative extrapolation, one can usually rely on the fact that a compound causing an effect in one mammalian species will cause it in another species" as reason enough to allow an expert to opine about Chantix' hypothesized effect on human metabolism based on its effect on the metabolism of one strain of mice. Let's test that assumption in light of some very good news out this week on aging research (well, good news if you don't like being on a near starvation diet for life).
Restricting caloric intake has long been known to dramatically increase life expectancy in mice. Experiments designed to test the effect in single celled organisms like yeast, microscopic multicellular organisms like nematodes (round worms), the always-ready-to-serve-mankind fruit fly and various strains of mice, rats, guinea pigs and even dogs have consistently shown that by reducing calorie intake by a third or more from what the creature would have consumed had it eaten until it was sated, lifespan is extended by 40% or more. Indeed, some studies have shown that the harder they're starved the longer rats live. The effect then would appear to be "highly conserved", which is to say evolution found the algorithm to be highly beneficial long ago and thus widely spread it throughout the chain of life. So it obviously follows that semi-starved people ought to live longer too, right?
Well, assuming we're closer kin to the Rhesus monkey (famed for helping to discover the human Rh blood factor) than to the Sprague Dawley rat it looks as though the metabolisms of mice and men are decidedly different. In an article published this week in Nature a 30% calorie restricted diet over 25 years failed to extend the lifespan of one of our closest relatives.
In retrospect the finding ought not be nearly as shocking as it was made out to be in the media. Click on some of the links above and you'll see that the earlier research findings were always far from unequivocal and universal. Some mice strains are little affected and many aspects of aging (like cognitive decline) have often been shown to be unaltered by caloric restriction even when lifespans were extended. And should we even be surprised by the result, given how much more complex humans are than mice? Experts extrapolating from mice to men ought to give courts pause so long as we can't reliably extrapolate from mice to monkeys.
