The diverse life-course cohort (DLCC): protocol of a large-scale prospective study in China.

The Diverse Life-Course Cohort (DLCC) is a large-scale prospective study including around 130,000 participants in mainland China. The primary aims of DLCC include contributing to knowledge on noncommunicable chronic disease determinants, particularly cardiometabolic diseases, and exploring the long-term effect of ambient air pollutants or other environmental risk factors on health among all-age populations. The cohort consists of several sub-populations that cover the whole life-course and diverse resources: from premarital to adolescents, adults from workplace and communities ranged from 18 to 93 years old. Baseline assessment (2017-2021) included face-to-face standardized questionnaire interview and measurements to assess social and biological factors of health. Blood samples were collected from each participant (except for children younger than 6) to establish the biobank. DLCC consists of two visits. Visit 1 was conducted from 2017, and 114850 individuals from one of the world-class urban agglomerations: Beijing, Tianjin, and Hebei area were recruited. By the end of 2021, at least one follow-up was carried out, with an overall follow-up rate of 92.33%. In 2021, we initiated Visit 2, newly recruited 9,866 adults from Guangdong province (South China) and Hebei province (Central China), with research focuses on the comparations on ambient pollution hazards and other unique dietary or environmental risks for health. The baseline survey of Visit 2 was finished in July 2021. DLCC is still ongoing with a long-term follow-up design, and not limited by the current funding period. With reliable data and the well-established biobank which consists of over 120,000 individuals' blood samples, DLCC will provide invaluable resources for scientific research.