Soy intake, all-cause and cause-specific mortality in Japan: the Jichi Medical School Cohort Study

Background: Soy is a popular ingredient in the Japanese diet. However, few studies have investigated the association between soy intake and mortality. This study aimed to determine whether soy intake was associated with all-cause mortality in a community-based cohort in Japan. Methods: Data were obtained from an annual community-based health examination program, with participants followed each year from 1992 to 2005. A total of 11 066 subjects (4309 men, 6757 women) were included. A self-administered questionnaire was used to collect information concerning potential confounding factors and soy intake which focused on boiled soy. Associations between soy intake and all-cause mortality were assessed using hazard ratios (HRs) with 95% confidence intervals (CIs) as determined by Cox proportional hazard models. Subjects who reported ingesting soy one to two times per week were used as a reference group. Results: After adjusting for all factors, mortality was significantly higher in men with infrequent soy intake (HR, 1.53; 95% CI: 1.13-2.07) and with almost daily intake (HR, 1.55; 95% CI: 1.19-2.03) compared with intake one to two times per week. Cancer mortality was higher among men who reported rarely eating soy (HR, 1.74; 95% CI: 1.08-2.79). Conclusions: Among men, compared with soy intake one to two times per week, infrequent or daily soy intake was associated with increased risk of all-cause mortality.