Pioneering experiments using heterochronic parabiotic anastomoses between young and older mice have reported the reversal of a number of age-related phenotypes in older mice. These studies have identified the growth differentiation factor 11 (GDF11) and oxytocin as important anti-geronic factors. However, the age- related changes in the circulating levels of these anti-geronic factors and their relation with age-related phenotypes within human populations remain poorly understood, due, in part, to issues of assay specificity. We will characterize age-related changes in GDF11 and oxytocin levels, determine their relation to age-related clinical events, conditions and subclinical markers related to cardia, brain, metabolic, and musculoskeletal aging, and elucidate their epigenomic and transcriptomic determinants in adults over a wide age range in the Framingham Heart Study (FHS) Offspring and Omni cohorts, n=3195), and replicate these findings in Atherosclerosis Risk in Communities (ARIC) Study (n=1966). We will determine the effects of caloric restriction on GDF11 and oxytocin levels in the CALERIE randomized trial. A major innovation of our study is the development of a specific liquid chromatography tandem mass spectrometry assay for GDF11 and a specific extraction immunoassay for oxytocin, which will overcome the problem of nonspecificity of extant assays. Aim 1 will characterize age-related changes in circulating GDF11 and oxytocin levels in men and women in the FHS Offspring and Omni cohorts and relate these changes to age, sex, and race/ethnicity. Aim 2 will relate GDF11 and oxytocin levels in cross-sectional and longitudinal analyses with age-related clinical events, conditions and phenotypes (primary for GDF11: mortality, CVD events, dementia; secondary: myocardial mass and function, cognitive function, brain structure, muscle strength and physical function; primary for oxytocin: mortality, mobility limitation, diabetes, fractures; secondary: grip strength gait speed; brain structure; cognition). We will assess the heritability of GDF11 and oxytocin levels, and identify DNA methylation (CpG sites) and transcriptomic (mRNA) correlates of variation in GDF11 and oxytocin levels and how they impact the relation of GDF11 and oxytocin levels with age-related phenotypes and conditions. Aims 1 and 2 will be replicated in the ARIC cohort. Aim 3 will determine the effects of caloric restriction on GDF11 and oxytocin levels. Exploratory mediator analyses will evaluate whether the relation of GDF11 with CVD events (e.g., heart failure) is mediated through its effects on myocardial mass, and whether its relation to dementia is mediated through structural changes in specific brain regions. The depth and breadth of the existing FHS and ARIC data provides a unique opportunity to determine whether age-related changes in GDF11 and oxytocin are linked to major aging-related clinical events of public health importance through subclinical aging-related measures. Our project will facilitate the development of anti- aging therapies that are aimed at modifying two anti-geronic factors of great promise.