Korean Soldiers Study
Year Begun: 1951
Location: South Korea
Principal Investigator: Enos, Jr., William
The Korean Soldiers study examined the development of atherosclerosis in young men killed while serving in the Korean War. The researchers examined the coronary arteries for evidence and magnitude of atherosclerosis.
Three hundred soldiers, most of whom were killed in action or accidentally, were autopsied, and their arteries were carefully dissected both cross-sectionally and longitudinally [1 and 2]. Complete data, including age, height and weight were collected for 200 of the subjects. Average age ranged from 18 to 48 years with a mean of 22.1 years, average height was 171 centimeters, and average weight was 66 kilograms. 
In measuring the extent of atherosclerosis, “occlusion was considered complete only when the plaque had no free surface and was fused to the wall opposite its point of origin. […] No actual measurements were made.”  The classification of atherosclerosis ranged from “fibrous thickening to large atheromatous plaques causing complete occlusion of one or more of the major vessels.”  No cases with a known history of coronary heart disease were included.
The arteries of Korean men were examined in a similar fashion. The investigators noted the intimal walls of the Koreans tended to be thicker, but that plaques rarely formed in the arteries. The investigators attributed the thickening to stress and the lack of blockage to dietary factors. 
In 77.3% of the hearts, some evidence of atherosclerosis was discovered.  For 35% of the cases, the disease was limited to “fibrous thickening or streaking causing insignificant luminal narrowing.”  For 13.3% of the population, plaques had narrowed the lumina by 10%. For 5.3% of the population, the lumina had narrowed by 90%.  For the majority of cases, the atherosclerotic lesions were found in the “proximal third of the left coronary artery […] usually thickest on the epicardial side of the lumen” or “in the distal third of the artery just proximal to the bifurcation of the circumflex artery in a more medial position.” 
The Korean Soldiers Study was one of the first to examine atherosclerotic development in a young population. It was also unique in its use of the autopsy of deceased soldiers to collect a cross-sectional sample. Limitations of the study included incomplete data recording and lack of sample description in terms of body type or any of the measures later termed coronary risk factors. Nevertheless, the study had a profound impact on the medical awareness of the mounting epidemic of coronary disease and its extension into young age groups by the mid-1950’s. (HB)
Footnote: A subsequent study among U.S. casualties in Vietnam some 20 years later suggested that fewer (45% vs. 77%) of similar young men had evidence of coronary atherosclerosis. Neither study had adequate quantitative methodology to provide more than the unadorned estimates. MacNamara et al 1971. JAMA: 216: 1185.
 Enos WF, Holmes RH, Beyer J. Coronary disease among United States soldiers killed in action in Korea. JAMA. 1953; 152 (12): 1090-1093.
 Enos WF, Beyer J, Holmes RH. Pathogenesis of coronary disease in American soldiers killed in Korea. JAMA. 1955; 158 (11): 912-914.