Estrogens also play a key role in regulation of bone mass and strength by controllingactivity of bone-forming osteoblasts and inhibiting activity and vitality ofbone-resorbing osteoclasts (100). Also Vina and colleagues (73) showed that estrogens play a protective role against oxidativestress. They exhibit an accelerated decline inmuscle mass and strength around the time of the menopause (2,4,90–95), which isrelated to this loss of estrogens (4,96) and causes subsequent decreases in function(76,97). This may be regulated byalteration the protein content of medium-chain acyl-CoA (MCAD), possibly throughperoxisome proliferator-activated receptor γ coactivator 1-α(PGC-1α)–mediated transcription and decrease of miR-29b, leading to increasedmitochondrial gene expression (MCAD and hippuric acid HA) and thus lipid utilization(89). The meta-analysis of Greising and colleagues (87) showed that postmenopausal women on estrogen hormone therapy hadgreater physical strength than those without treatment. However, deficiencies inmultiple anabolic hormones have been shown to predict health status and longevity in olderpersons. In men, reductions in testosterone can trigger declines in muscle mass, bonemass, and in physical function. It's best to measure free testosterone levels in the morning. Checking testosterone levels is as easy as having a blood test. Men and women need the proper amount of testosterone to develop and function normally. A larger trial of exogenous testosterone on cardiovascular disease is now underway in men23. A small trial of exogenous testosterone in frail older men was stopped early because of adverse events in the testosterone arm22, but is difficult to interpret. Discrepant findings in trials compared to observational studies have been ascribed to overlooked confounding by socio-economic position in the observational studies9. Large-scale trials of estrogen in women and men were stopped early for harm or lack of benefit9. Observational evidence concerning benefits of exogenous estrogen in women was very promising8. As the long-term trend of increasing life expectancy in the West now appears to be stagnating7, reconsidering overlooked targets and their implications for the design of interventions might bear consideration. Given this is a hypothesis driven study, with a positive and a negative control, we used a statistical significance level of 0.05. Where necessary we combined estimates for men and women using IVW meta-analysis. Bio-available testosterone may also be a more sensitive indicator that total testosterone of active testosterone in men69. We obtained the F-statistics for the genetic instruments using an established approximation (square of genetic variant on exposure divided by its variance)66. Reprogramming cells towards self-rejuvenation seems to solve the mystery of longevity and a sought-after element of the philosopher’s stone. Sirtuins might potentially protect the kidneys, maintaining homeostasis of podocytes damaged with age. They have the potential to counteract the aging process by modulating the response of cells to stress, changing their pattern, and restoring tissue homeostasis responsible for phenotypic aging . Sirtuins are products of the Sir-2 gene, which along with the p66shc, ink4a, FOXO, and daf-2 genes, is referred to as the longevity gene . We used published sex-specific genetic predictors of testosterone (125 variants for men and 254 for women)28. Fourth, our study gives lifetime effects of endogenous testosterone up to age ~ 57 years rather than the effect of an intervention. Explicitly, searching sex-specifically for interventions based on this insight might facilitate the search for new means of promoting healthy aging by identifying at an early stage any potential interventions that are likely to be unsuccessful, and where interventions should be sex-specific. Our findings differ from previous observational studies which suggest that endogenous testosterone might improve health and lifespan10–14. As such, longevity studies, take advantage of the changing structure of risk factors with age to obtain estimates of effects on mortality free from selection bias34.
