Kei Hamazaki¹ MD, PhD, Hiroyasu Iso² MD, PhD, Ehab S. Eshak^2,3 MD, PhD, Satoyo Ikehara^2,4 PhD, Ai Ikeda^2,5 PhD, Motoki Iwasaki⁶ MD, PhD, Tomohito Hamazaki⁷ MD, PhD, Shoichiro Tsugane⁶ MD, PhD, for the JPHC Study Group

1. Department of Public Health, Faculty of Medicine, University of Toyama, Toyama, Japan
2. Public Health, Department of Social Medicine, Osaka University Graduate School of Medicine, Osaka, Japan
3. Department of Public Health and Preventive Medicine, Faculty of Medicine, Minia University, Egypt
4. Department of Hygiene and Public Health, Osaka Medical College, Osaka, Japan
5. Department of Public Health, Juntendo University, Tokyo, Japan
6. Epidemiology and Prevention Group, Center for Public Health Sciences, National Cancer Center, Tokyo, Japan
7. Toyama Jonan Onsen Daini Hospital, Toyama, Japan.

Background: Higher intake of fish or n-3 polyunsaturated fatty acids (PUFAs) has been associated with reduced risk of coronary heart disease (CHD). However, it is unclear whether increased blood levels of n-3 PUFAs are associated with reduced risk of CHD in the Japanese population.

Methods: The relationship between circulating levels of n-3 PUFAs (eicosapentaenoic acid + docosapentaenoic acid + docosahexaenoic acid) and risk of CHD was examined in a nested case-control study among participants in the Japan Public Health Center (JPHC)-based Study Cohort. Plasma n-3 PUFA phospholipid levels were measured at baseline by gas chromatography in 209 cases with CHD and 418 controls matched for sex, age, date of blood draw, time elapsed since last meal before blood collection, and study location. The CHD cases (n=209) involved 168 cases of myocardial infarction and 41 of sudden cardiac death, otherwise classified as 157 non-fatal and 52 fatal coronary events, respectively.

Results: Multivariate conditional logistic analysis showed no significant association between n-3 PUFAs and risk of total CHD. Subtype analysis of CHD revealed that the multivariate ORs for the highest versus lowest quartiles were significantly lower for sudden cardiac death and fatal coronary events but not for myocardial infarction and for nonfatal coronary events.

Conclusion: Plasma n-3 PUFA levels were not associated with risk of total CHD but were inversely associated with risks of sudden cardiac death and fatal coronary events among middle-aged Japanese individuals.