Introduction
Chronic pain is common in older people. There is limited evidence for the predictors of chronic pain in old age. It is important to identify risk factors for chronic pain because they can guide preventive interventions and improve clinical management. In the general population, the predictors of chronic pain are constant. They are: Age, female gender, low social class, socioeconomic status, properties of pain (severity and number of pain points), psychological disorders (anxiety, depression), comorbidities, and genetic factors [7]. Therefore, given that chronic pain in older people is common, the need to find out factors linked to chronic pain in the older population to develop treatment strategies and prevention for chronic pain is imperative. This study aims to investigate the factors related to chronic pain in older adults living in Amirkola City, Mazandaran, north of Iran.

Methods 
This is a descriptive-analytical study with a cross-sectional design, as a second phase of the Amirkla health and ageing project (AHAP) cohort study. Participants were 1675 older adults living in Amirkola City. They were divided into two groups depending on whether they had chronic pain or not. Their demographic factors, cognitive status using the mini-mental state examination (MMSE), depressive symptoms using the geriatric depression scale (GDS), sleep quality using the Pittsburgh sleep quality index (PSQI), frailty using the FRAIL scale, and physical activity using the physical activity scale for the elderly (PASE), were measured.
Demographic information included age, sex, educational level, marital status, occupation, level of satisfaction with income, and use of sleeping pills, which were surveyed using a demographic form.
Chronic musculoskeletal pain and its location were surveyed using a questionnaire. Older people were asked if they had experienced pain in any of the following areas in the last six months, lasting for 3 months or longer: Hands, wrists, elbows, shoulders, face, jaw, neck, hip joints, knees, ankles, feet, and back.
The collected data were analyzed in SPSS software, version 24 using chi-square, t-test, and multiple logistic regression analysis. P<0.05 was considered statistically significant.

Results
The participants were mostly male, married, illiterate, and housekeepers. The majority of the elderly (76.52%) were pre-frail or frail. Chronic pain was significantly more common among unmarried women, those with a low level of education, those living alone, housewives, those unsatisfied with their income, disabled people, users of sleeping pills, those with poor sleep quality, and those with depressive symptoms. The mean age, GDS score, PSQI score, and the number of chronic diseases were significantly higher and the PASE and MMSE scores were significantly lower in the group with chronic pain than those without chronic pain. The results of multivariate logistic regression analysis with Enter method showed that number of chronic diseases, depressive symptoms and sleep disorder had the highest association with chronic pain (Table 1).


The mean PSQI score was higher in older women and men with chronic pain using sleeping pills (Figure 1).

Conclusion
In Amirkola City, 67.6% of older adults suffer from chronic pain, most of whom are women and those higher with higher age.  The chronic pain in older adults is strongly associated with sleep quality disorders, depressive symptoms, and the number of chronic diseases.
The development of appropriate interventions based on these factors to reduce the chronic pain of older adults is recommended.

Ethical Considerations
Compliance with ethical guidelines
This study was approved by the Ethics Committee of Babol University of Medical Sciences, Babol, Iran (Code: IR.MUBABOL.HRI.REC.1398.352). After providing initial explanations, informed consent was obtained from all participants or their legal guardians. All procedures were performed in accordance with relevant guidelines. 

Funding
This study was funded by Babol University of Medical Sciences, Babol, Iran (Grant Number: 724132234).

Authors' contributions
Design, writing and investigation: Seyed Reza Hosseini, Ali Zabihi and Mahdieh Hosseininejad Roshan; editing and review: Seyed Reza Hosseini, Reza Ghadimi, Alireza Sefidchian, Alijan Ahmadi Ahangar, and Ali Zabihi; data analysis: Ali Bijani; preparation of the initial draft: Ali Zabihi and Mahdieh Hosseininejad; Final approval: all authors.

Conflicts of interest
The authors declared no conflict of interest.

Acknowledgements
The authors would like to thank the Vice-Chancellor for Research and Technology of Babol University of Medical Sciences, Babol, Iran, for financial support, the staff of the health centers in Amirkola for their cooperation in this study, and all seniors for participating in this study.

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