Journal of Neurology

, Volume 266, Issue 5, pp 1222–1229 | Cite as

Joint impact of seven risk factors on incident dementia in elderly Japanese: the Ohsaki Cohort 2006 Study

  • Yumika Kotaki
  • Yasutake TomataEmail author
  • Fumiya Tanji
  • Shu Zhang
  • Yumi Sugawara
  • Ichiro Tsuji
Original Communication



This cohort study estimated the population attributable fraction (PAF) of seven combined major risk factors for incident dementia.


We conducted a cohort study of 8563 community-dwelling individuals aged ≥ 65 years. In a baseline survey (2006), we collected data on major seven risk factors: diabetes mellitus, hypertension, obesity, physical inactivity, severe psychological distress, smoking, and low educational attainment. The total number of risk factors was applied as an exposure variable. Subjects were categorized into four groups according to the total number of risk factors they possessed (0, 1, 2, ≥ 3 risk factors). Data on incident dementia were retrieved from the public Long-term Care Insurance database. Hazard ratios (HRs) and 95% confidence interval (95% CI) were estimated using the Cox proportional regression model. We also calculated the PAF using HRs and the prevalences in our cohort data.


The number of cases of incident dementia was 577 (6.7%). A dose–response relationship between the total number of risk factors and incident dementia was observed; in comparison with no risk factors (reference), the age- and sex-adjusted HRs (95% CIs) were 1.25 (0.92–1.70) for one risk factor, 1.59 (1.18–2.15) for two, and 2.21 (1.62–3.01) for three or more (P trend < 0.001). If subjects had adhered to none of the risk factors, the PAF would have been 32.2%. If subjects had improved toward one better category, the PAF would have been 23.0%.


Our findings suggest that reducing the combined number of risk factors would contribute significantly to reducing the incidence of dementia.


Dementia Joint effect Cohort Attributable fraction Risk factors 



The authors thank Yoshiko Nakata, Mami Takahashi, Miyuki Takeuchi, and Yuko Miyoshi for their technical assistance.

Author contributions

YK, YT and IT designed research. YT and IT conducted research. YK, FT, YT and SZ analyzed data. YK wrote the paper. YT, FT, YS, SZ and IT gave the constructive suggestions. YK had primary responsibility for final content. All authors read and approved the final manuscript.


This work was supported by a Grant-in-Aid for Young Scientists (B; 17K15844) from the Japan Society for the Promotion of Science.

Compliance with ethical standards

Conflicts of interest

The authors declare that they have no conflict of interest.

Ethical standards

The study protocol was reviewed and approved by the Ethics Committee of Tohoku University Graduate School of Medicine (Sendai, Japan) (Approval number: 2006-206, 2013-1-289). The study has been performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments.

Supplementary material

415_2019_9252_MOESM1_ESM.pdf (316 kb)
Supplementary material 1 (PDF 316 KB)


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  • Yumika Kotaki
    • 1
  • Yasutake Tomata
    • 1
    Email author
  • Fumiya Tanji
    • 1
  • Shu Zhang
    • 1
  • Yumi Sugawara
    • 1
  • Ichiro Tsuji
    • 1
  1. 1.Division of Epidemiology, Department of Health Informatics and Public HealthTohoku University School of Public Health, Graduate School of MedicineSendaiJapan

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