selected from a database of pooled controls that is maintained by Japan's Research
Committee on the Epidemiology of Intractable Diseases. The database contains
information about a wide range of lifestyle risk factors for 73,861 men and women
throughout Japan aged between 20 and 79 years at the time of control recruitment. Every
available control in the population of pooled controls was selected for the present study.
This method enabled data from a large number of population-based controls to be obtained
cost-efficiently. Data for a total of 20,313 controls were finally used in the analyses.