Doubts on Klotho
From Ouroboros: "The soluble protein Klotho appears to be an anti-aging factor, since mice deficient in the Klotho gene show signs of premature aging. However, the validity of Klotho-/- mutants as a model of progeria is controversial: many of the pathological features of the mutant phenotype can be attributed to hypervitaminosis D, and can be reversed by eliminating vitamin D from the diet. (Biogerontologists are generally more skeptical of progeria than increased longevity, since there are lots of ways to shorten lifespan that don't involve bona fide accelerating of the aging process, whereas there are far fewer ways to lengthen lifespan without slowing that process down.) Another blow against the idea of Klotho as a regulator of lifespan comes from Brownstein et al. ... from a biogerontological perspective, it's both interesting and sad: Specifically, it’s a strike against the idea that we might be able to supplement aging mammals (like ourselves) with increased levels of Klotho in order to forestall aging."
Link: http://ouroboros.wordpress.com/2008/04/17/time-to-retire-klotho-as-an-anti-aging-factor/