The Medical Research Council (MRC) National Survey of Health and Development (NSHD), also known as the 1946 British birth cohort study, is the oldest and longest-running British birth cohort study. It has tracked 5,362 individuals born in one week in March 1946 across England, Scotland, and Wales. The study initially aimed to understand how home and school environments influenced physical and mental development and educational attainment during childhood. As participants aged, the focus shifted to examining how early life health and social circumstances impact adult health and aging processes. Participants have been assessed 25 times, with recent assessments including clinic visits and home visits to gather data on health, lifestyle, and cognitive function. The NSHD provides valuable insights into the lifelong biological and social factors influencing aging.