Extracellular Mass to Body Cell Mass Ratio As Novel Index of Healthy Aging

Health (DiAL Health) planning project, we conducted three substudies to assess the feasibility of such studies, as well as strategies for enrolling young, healthy individuals for longitudinal investigations of human aging.Methods: In sub-study one, we determined the costs of our recruitment efforts to enroll 70 healthy, young (25 -49 years), unmedicated individuals without obesity (BMI 22 -29.9 kg/m 2 ) across two DiAL Health sites.In sub-study two, we assessed what fraction of the US population meets partial trial eligibility criteria using National Health and Nutrition Examination (NHANES) Survey data (2017( -March 2020)).In sub-study three, we conducted a formative research study of 492 U.S. adults (! 18 years) to assess participants who met full trial eligibility interest in engaging in dietary intervention trials with a focus on aging endpoints.Results: In DiAL Health, 2,049 participants were screened, of whom 70 enrolled (3.4% enrollment rate).Costs per participant enrolled were $1,572 for study site 1 and $625 for site 2, and optimal recruitment methods varied by site.NHANES data showed that only 3.6% of the U.S. adult population (555 of 15,560 individuals) met partial eligibility criteria for the trial.In sub-study 3, we found that only 2.2% (11 of 492) of survey respondents met the full eligibility criteria for DiAL Health.Overall, eligible participants were willing to be randomized to dietary interventions like time-restricted eating and caloric restriction, though willingness decreased when longer interventions were proposed.Conclusions: Conducting even short-term aging trials in young, healthy individuals is challenging as: 1) only ~2-3% of adults in the U.S. are eligible, and 2) only ~3-4% of screeners enroll, and this percentage will likely be lower in longer more burdensome studies.These results highlight the recruitment burden and cost of recruiting healthy young samples of participants.