Psychosocial factors are known to affect knee pain. However, the magnitude of depression on the associations between socioeconomic status (SES) and knee pain in older individuals remains unknown. This study aimed to determine (1) the associations between SES and knee pain and (2) how depression mediates the associations between SES and knee pain.
We conducted a survey across 30 Japanese municipalities to collect cross-sectional data. Functionally independent, community-dwelling adults aged 65 years or above (n=26,037) were eligible for the study. Self-reported knee pain in the past year was used as the dependent variable. Past occupation and equivalized household income were separately added to the models as independent variables. Poisson regression analysis was used to examine the associations between SES and knee pain, adjusting for covariates. Mediation analysis was applied to estimate how depression explains these associations.
The 1-year prevalence of knee pain was 56.0% in our study population. We found that income levels were significantly associated with knee pain: the lowest income level was more prone to experience knee pain compared with the highest income level at a prevalence ratio of 1.22 (95% confidence interval, 1.15-1.28). Depression explained 36.8% of the association of income with knee pain in females and 41.9% in males.
Significant socioeconomic inequalities were observed regarding knee pain among older individuals in Japan. Depression somewhat explained the association between SES and knee pain.
*Department of Health Policy Science, Graduate School of Medical Science, Yamagata University, Yamagata
†Department of International and Community Oral Health, Tohoku University Graduate School of Dentistry, Sendai
‡Center for Preventive Medical Sciences, Chiba University, Chiba
§Center for Gerontology and Social Science, National Center for Geriatrics and Gerontology, Aichi, Japan
T.K.: conception, methodology, analysis, manuscript composition, and approval. J.A.: conception, methodology, acquisition of data, analysis, manuscript composition, and approval. T.T. and K.S.: conception, methodology, manuscript composition, and approval. K.K. and K.O.: conception, acquisition of data, methodology, manuscript composition, and approval.
Supported by a grant of the Strategic Research Foundation Grant-aided Project for Private Universities from the Ministry of Education, Culture, Sport, Science, and Technology, Chiyoda, Tokyo, Japan, 2009-2013, for the Center for Well-being and Society, Nihon Fukushi University, Grants-in-Aid for Scientific Research (22330172, 22390400, 22390400, 22592327, 23243070, 23590786, 23790710, 24390469, 24530698, 24653150, 24683018, 25253052, 25870573, 25870881, 26285138, 26882010, 15H04781, 15H01972, 16H05556, 16K19267, 18KK0057, 19K19818) from the Japan Society for the Promotion of Science, Chiyoda, Tokyo, Japan. The study was also supported by a Health and Labour Sciences Research Grant, and grants for Comprehensive Research on Aging and Health (H22-Choju-Shitei-008, H24-Junkankitou-Ippan-007, H24-Chikyukibo-Ippan-009, H24-Choju- Wakate-009, H25-Kenki-Wakate-015, H25-Irryo-Shitei-003 [Fukkou], H26-Choju-Ippan-006, H27-Ninchisyou-Ippan-001, H28-Choju-Ippan-002) from the Ministry of Health, Labour and Welfare, Chiyoda, Tokyo, Japan, the Research and Development Grants for Longevity Science from AMED (Japan Agency for Medical Research and Development, Chiyoda, Tokyo, Japan, the Personal Health Record [PHR] Utilization Project from AMED, Chiyoda, Tokyo, Japan, World Health Organization Centre for Health Development [WHO Kobe Centre], Kobe, Hyogo, Japan. WHO APW 2017/713981), Japan Foundation for Aging and Health Research Support Grant, Aichi, Japan, as well as grants from National Center for Geriatrics and Gerontology, Aichi, Japan. The research funding bodies had no role in the study design, data collection, data analysis, data interpretation, writing, or submitting of the report. The authors declare no conflict of interest.
Reprints: Jun Aida, DDS, PhD, Department of International and Community Oral Health, Tohoku University Graduate School of Dentistry, Sendai, 4-1, Seiryo-machi, Aoba-ku, Sendai 980-8575, Miyagi Prefecture, Japan (e-mail: firstname.lastname@example.org).
Received September 25, 2018
Received in revised form May 15, 2019
Accepted August 29, 2019
Online date: September 10, 2019