Open Access Research article

Relationship between soy and isoflavone intake and periodontal disease: The Freshmen in Dietetic Courses Study II

Keiko Tanaka1*, Satoshi Sasaki2, Kentaro Murakami2, Hitomi Okubo3, Yoshiko Takahashi4, Yoshihiro Miyake1 and for the Freshmen in Dietetic Courses Study II Group

Author Affiliations

1 Department of Public Health, Faculty of Medicine, Fukuoka University, Fukuoka, Japan

2 Department of Social and Preventive Epidemiology, School of Public Health, The University of Tokyo, Tokyo, Japan

3 Department of Nutrition Sciences, Kagawa Nutrition University, Saitama, Japan

4 Department of Health and Nutrition, Wayo Women's University, Chiba, Japan

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BMC Public Health 2008, 8:39  doi:10.1186/1471-2458-8-39

Published: 29 January 2008



Much research has shown that soy products inhibited various diseases. However, no published studies have examined the effects of consumption of soy and isoflavones on periodontal disease. The aim of this study was to investigate whether soy and isoflavone intake is associated with the prevalence of periodontal disease.


The subjects were 3956 Japanese female students, aged 18 to 22 years, who were taking a dietetic course. Periodontal disease was defined as present when a subject reported diagnosis of the disorder by a dentist. Information on dietary factors was collected using a validated diet history questionnaire. Logistic regression analysis was used to estimate the odds ratios and their confidence intervals of periodontal disease. Adjustment was made for cigarette smoking, toothbrushing frequency, region of residence, and body mass index.


The prevalence of periodontal disease was 8.0%. Intake of total soy product and tofu was independently associated with a decreased prevalence of periodontal disease; multivariate odds ratios in comparison of the highest with the lowest quintile were 0.68 and 0.68, respectively (95% confidence intervals = 0.47–0.97 and 0.47–0.98, P for trend = 0.01 and 0.004, respectively). A significant inverse dose-response relationship between the intake of isoflavones and the prevalence of periodontal disease was observed, although the difference in the adjusted odds ratio between the extreme quintiles was of borderline significance (P for trend = 0.04). There were no measurable dose-response relationships between consumption of tofu products, fermented soybeans, boiled soybeans, miso, or miso soup and the prevalence of periodontal disease.


Our findings suggest that soy and isoflavone intake may decrease the likelihood of periodontal disease. Further investigations with objective measures for periodontal disease are needed to confirm our findings.