The Nurses' Health Study is a long-term research project that began in 1976, focusing on the health of registered nurses in the United States. It aims to investigate the relationships between lifestyle factors, diet, and various health outcomes, including chronic diseases like heart disease and diabetes. Over 120,000 nurses participated, providing valuable data through questionnaires about their health and habits. The study has significantly contributed to our understanding of women's health and has influenced public health guidelines and policies related to nutrition and preventive care.