Objective: To report the rational, design, recruitment, baseline characteristics and preliminary overview of volunteers in the ZENITH study. Design: A multicentre prospective intervention study employing a randomised double-blind design. Setting: Clermont-Ferrand, Theix (France), Coleraine (Northern Ireland), Grenoble (France), Rome (Italy). Participants: Healthy men and women middle-aged (55-70 y) and older volunteers (70-87 y). Interventions: At baseline (prior to zinc (Zn) supplementation), all volunteers underwent a full clinical examination, anthropometric measurements, health and lifestyle questionnaire, Mini Mental State Examination, Geriatric Depression Scale, and biochemistry profile. Results: In total, 842 volunteers (378 men and 464 women) were invited to take part in the study. A total of 49% of these volunteers were excluded on the basis of inclusion/exclusion criteria. In total, 433 participants were admitted to the Zn supplementation for 6 months. During this period, about 10% of volunteers dropped out from the study. Conclusions: A total of 387 subjects (1197 male and 190 female subjects) successfully completed the supplementation phase of the ZENITH study.