The fourth investigation was performed when the men were aged 77 years. Until 18 Nov 1997, the date for the invitation, 748 of the 2322 participants at age 50 had died. Another 176 men were ineligible for other reasons and 1398 men were invited to this investigation. Of the invited, 839 men (60.0%) attended the investigation.
The first 44 participants only performed a mini mental test. Plasma/serum samples were available from 788 individuals and urine samples from 706 individuals.