A 15-year cohort study of self-reported fermented soybean (natto) intake and all-cause mortality in elderly men

Fermented soy foods come in different forms, each with varying effects on mortality. However, few epidemiological studies have investigated the effect of intake of individual types of fermented soy products on mortality. The present study aimed to investigate the association between intake of fermented soybeans, 'natto,' and all-cause mortality in community-dwelling elderly men, with a follow-up duration of approximately 15 years.

This prospective cohort study included 2174 men aged ≥65 years, of whom 2012 completed the baseline survey. Follow-up surveys were conducted five and 10 years later with mortality as the outcome. Participants completed a questionnaire regarding dairy natto intake. Hazard ratios (HRs) were calculated for the association between natto intake and all-cause mortality using Cox proportional hazards models.

The final analysis population consisted of 1548 men. During a mean follow-up period of 12.0 years (18553.3 person-years), 430 deaths were identified. Compared with 'no consumption' of natto, HRs for 'several packs/week' and 'pack/day or more' were 0.603 (95 % confidence interval (CI) 0.441 to 0.825) and 0.786 (95 % CI 0.539 to 1.145), respectively. Compared with the category "No consumption at both baseline and first follow-up," the HR for the category "Combination of several packs/week and one pack/day at baseline and first follow-up or several packs/week at both baseline and first follow-up" was 0.700 (95 % CI 0.507 to 0.966).

Habitual high intake of natto, especially over a long term, was associated with a lower risk of all-cause mortality in elderly men.