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It has been recently argued that during years of famine, it may be evolutionarily desirable for an organism to avoid reproduction and to up-regulate protective and repair enzyme mechanisms to try to ensure that it is fit for reproduction in future years. This argument seems to be supported by recent work studying hormones.[78] A study on male mice found that CR generally feminizes gene expression, and that many of the most significantly changed individual genes are involved in aging, hormone signaling, and p53-associated regulation of the cell cycle and apoptosis; it concluded that the life-extending effects of CR may arise partly from a shift toward a gene expression profile more typical of females.[79] Prolonged severe CR lowers total serum and free testosterone while increasing SHBG concentrations in humans; these effects are independent of adiposity.[80] See also: Insulin#Physiological effects Lowering of the concentration of insulin and substances related to insulin, such as insulin-like growth factor 1 and growth hormone, has been shown to up-regulate autophagy, the repair mechanism of the cell.[81] A related hypothesis suggests that CR works by decreasing insulin levels and thereby up-regulating autophagy,[81][82] but CR affects many other health indicators, and it is still undecided whether insulin is the main concern.[50] Calorie restriction has been shown to increase DHEA in primates, but it has not been shown to increase DHEA in post-pubescent primates.[83][84] The extent to which these findings apply to humans is still under investigation. |
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