The Ni-Hon-San study began in 1965 as a clinical study of cardiovascular risk factors in a population of men who live in Hiroshima, Japan, and Honolulu, Hawaii. In 1969 similar observations began in San Francisco, California; hence, the use of the acronym “Ni-Hon-San” (Nippon-Honolulu-San Francisco). In this study, the Adult Health Study participants have been compared with Japanese living in Honolulu and San Francisco to see how the differences in environment, diet, and lifestyle influence the incidence of cardiovascular diseases and mortality. The Ni-Hon-San cohort included all males participating in the Adult Health Study who were born from 1895 to 1924.

Although follow-up of the California population ceased in the mid-1970s, the groups living in Japan and Hawaii continue to be studied.