Depressive disorders are the most prevalent mental health problems in the general population.1 In community studies from 30 countries the point prevalence of depression has been estimated at 12.9%.Reference Lim, Tam, Lu, Ho, Zhang and Ho2 Among middle-aged and older adults in six low- and middle-income countries, the prevalence of depression was 7.5%, with the highest rate in India (15.2%),Reference Lotfaliany, Hoare, Jacka, Kowal, Berk and Mohebbi3 and among ageing adults 27.9% had depressive symptoms in ChinaReference Guo, Kong, Fang, Zhu and Zhang4 and 11.5% in Malaysia.Reference Ahmad, Abd Razak, Kassim, Sahril, Ahmad and Harith5 In Thailand, in the general adult population, 2.5% had a major depressive disorder;Reference Assanangkornchai, Nontarak, Aekplakorn, Chariyalertsak, Kessomboon and Taneepanichskul6 and among older adults 18.5% had depressive symptoms in Chachoengsao ProvinceReference Charoensakulchai, Usawachoke, Kongbangpor, Thanavirun, Mitsiriswat and Pinijnai7 and 28.5% in Kanchanaburi.Reference Haseen and Prasartkul8 Late-life depression is associated with various negative consequences, including impairment in social functioning, reduced quality of life, increased comorbidity, lower medication adherence and increased suicidal behaviour.Reference Wen, Liu, Liao, Yin and Wu9
Owing to a demographic and epidemiological transition in Thailand, non-communicable diseases, including mental disorders such as depression, have become more prevalent.Reference Anantanasuwong, Narot and Kiettikunwong10–Reference Kaufman, Chasombat, Tanomsingh, Rajataramya and Potempa12 Considering that previous studies on depression in Thailand were cross-sectional, the prevalence of incident and persistent depressive symptoms among middle-aged and older adults in Thailand is unclear, as are the prospective relationships between baseline indicators and incident and persistent depressive symptoms. A greater understanding of the prevalence of incident and persistent depressive symptoms and of the factors associated with their occurrence may help in better identifying and addressing modifiable risk factors in the population.
Various longitudinal studies have identified health indicators associated with incident and/or persistent depression in middle-aged and older adults, including lifestyle factors (smoking, heavy alcohol use),Reference Cabello, Miret, Caballero, Chatterji, Naidoo and Kowal13 physical inactivity,Reference Cabello, Miret, Caballero, Chatterji, Naidoo and Kowal13,Reference Schuch, Vancampfort, Firth, Rosenbaum, Ward and Silva14 body weightReference Luo, Li, Zhang, Cao, Ren and Fang15,Reference Luppino, de Wit, Bouvy, Stijnen, Cuijpers and Penninx16 and specific chronic diseases, such as stomach/digestive diseases,Reference Wen, Liu, Liao, Yin and Wu9,Reference Bi, Pei, Hao, Yao and Wang17 diabetes,Reference Wen, Liu, Liao, Yin and Wu9,Reference Huang, Dong, Lu, Yue and Liu18 arthritis/rheumatism,Reference Wen, Liu, Liao, Yin and Wu9,Reference Huang, Dong, Lu, Yue and Liu18–Reference Xue, Pan, Gong, Wen, Peng and Pan20 liver disease,Reference Jiang, Zhu and Qin19 kidney disease,Reference Wen, Liu, Liao, Yin and Wu9,Reference Bi, Pei, Hao, Yao and Wang17,Reference Jiang, Zhu and Qin19,Reference Jia, Li, Liu, Shi, Liu and Cao21 sensory loss,Reference Huang, Dong, Lu, Yue and Liu18 hypertension,Reference Huang, Dong, Lu, Yue and Liu18,Reference Jin, Luo and He22 cardiovascular disease,Reference Huang, Dong, Lu, Yue and Liu18,Reference Jiang, Zhu and Qin19,Reference Chireh and D'Arcy23,Reference Yang, Wang, Chiu, Wu, Handa and Liao24 chronic lung disease,Reference Wen, Liu, Liao, Yin and Wu9,Reference Bi, Pei, Hao, Yao and Wang17,Reference Huang, Dong, Lu, Yue and Liu18 mild cognitive impairment and dementia,Reference Snowden, Atkins, Steinman, Bell, Bryant and Copeland25 memory-related diseaseReference Leung, Fan and Mahadevan26 and cancer.Reference Jiang, Zhu and Qin19 A higher number of chronic diseases was associated with a higher risk of incident depression.Reference Bi, Pei, Hao, Yao and Wang17,Reference Chang-Quan, Xue-Mei, Bi-Rong, Zhen-Chan, Ji-Rong and Qing-Xiu27 Other risk factors for depression may include low social support, adverse life events, and biological and sociodemographic factors.Reference Ortiz, García and Castillo28–Reference Peltzer and Pengpid30 There is a lack of longitudinal studies in Southeast Asia investigating determinants of incident and persistent depressive symptoms. To address this research gap, our objective was to investigate the prevalence of incident and persistent depressive symptoms and factors associated with their occurrence in a prospective cohort study among ageing adults (≥45 years) in Thailand.
Method
Sample and procedure
We analysed longitudinal data from two waves (2015 and 2017) of the Health, Aging and Retirement in Thailand (HART) study. In a three-stage (region, province, blocks or villages) stratified random sampling in each household, one person (≥45 years) was randomly selected. For frail respondents proxy interviews were administered.Reference Anantanasuwong, Theerawanviwat, Siripanich, Gu and Dupre31,Reference Anantanasuwong, Pengpid and Peltzer32 In the 2015 (n = 5616) and the 2017 surveys (n = 3708) the response and retention rates were 72.3% and 66.0% respectively; at follow-up 192 had died, 1554 had moved away from the study area and 270 declined participation.
Participants were interviewed using a structured questionnaire in 2015 and using computer-assisted personal interviewing (CAPI) in 2017. The study was approved by the Ethics Committee in Human Research at the National Institute of Development Administration – ECNIDA (ECNIDA 2020/00012) and participants gave their written informed consent.
Measures
Outcome variable
Participants completed the Center for Epidemiologic Studies Depression Scale (CES-D-10), and scores ≥10 were defined as indicating the presence of depressive symptoms.Reference Andresen, Malmgren, Carter and Patrick33 The CES-D-10 is valid in Thai adult populations.Reference Nilmanut, Kuptniratsaikul, Pekuman and Tosayanonda34,Reference Mackinnon, McCallum, Andrews and Anderson35 The internal consistency of the CES-D-10 in the study population ranged from 0.72 in 2017 to 0.78 in 2015.
Covariates
Sociodemographic variables included education, marital status, gender, age, education, religion and subjective economic status.
Substance use included alcohol use and smoking (tobacco use), rated as never, past or current.
Physical activity was classified as 0–149 min/week exercise and ≥150 min/week exercise.Reference Kim36,37
Body mass index (BMI), calculated from self-reported height and weight, was stratified as: underweight (<18.5 kg/m2), normal weight (18.5–22.9 kg/m2), overweight (23–24.9 kg/m2) and obesity (≥25 kg/m2).Reference Wen, David Cheng, Tsai, Chan, Hsu and Hsu38
Social participation (at least one social activity in the past month) was sourced from six items.Reference Berkman, Sekher, Capistrant, Zheng, Smith and Majmundar39
Participants were asked about 12 conditions diagnosed by a healthcare provider: hypertension; diabetes; vascular diseases, heart disease or heart failure; rheumatism or arthritis; bone diseases, low bone density or osteoporosis; kidney disease; lung disease/emphysema; cancer; liver disease; Alzheimer's disease/brain diseases; visual impairment; and hearing impairment. The 12 chronic diseases were classified into 8 groups: (a) cardiovascular: hypertension, heart disease, cardiovascular disease, heart failure; (b) endocrine (diabetes); (c) musculoskeletal (arthritis/rheumatism, osteoporosis and bone diseases); (d) liver or kidney disease; (e) respiratory (lung disease/emphysema); (f) cancer; (g) sensory (visual impairment and/or hearing impairment); and (h) neurological (brain diseases/Alzheimer's disease).
Statistical analysis
Frequencies and percentages of incident and persistent depressive symptoms were calculated. The first longitudinal logistic regression model estimated incident depressive symptoms in 2017, excluding those with depressive symptoms in 2015, and the second model estimated persistent depressive symptoms (in both 2015 and 2017). Models were adjusted by chronic diseases, sociodemographic factors, lifestyle factors, social participation and BMI; confounders were included based on literature review.Reference Wen, Liu, Liao, Yin and Wu9,Reference Bi, Pei, Hao, Yao and Wang17 P ≤ 0.05 was considered statistically significant. Missing data were discarded. Statistical analyses were conducted with Stata SE version 15.0 for Windows.
Results
Sample characteristics
In total, 290 of 4528 participants without depressive symptoms in 2015 had incident depressive symptoms in 2017 (9.8%), and 76 of 640 adults had persistent depressive symptoms (in both 2015 and 2017) (18.3%). The details of the sample are shown in Table 1.
Associations with incident depressive symptoms
In adjusted logistic regression analysis, having diabetes (adjusted odds ratio AOR = 1.48, 95% CI 1.07–2.05), musculoskeletal conditions (AOR = 1.56, 95% CI 1.01–2.41) and having three or chronic conditions (AOR = 2.55, 95% CI 1.67–3.90) were positively associated and a higher subjective economic status (AOR = 0.47, 95% CI 0.31–0.72) and social participation (AOR = 0.66, 95% CI 0.49–0.90) were inversely associated with incident depressive symptoms. In addition, in the unadjusted analysis, cardiovascular, sensory and neurological conditions were positively associated with incident depressive symptoms (Table 2).
COR, crude odds ratio; AOR, adjusted odds ratio.
a. adjusted for all variables except for individual chronic conditions.
* P < 0.05, **P < 0.01, ***P < 0.001.
Associations with persistent depressive symptoms
In adjusted logistic regression analysis, having a cardiovascular condition (AOR = 1.55, 95% CI 1.01–2.39) and having three or more chronic conditions (AOR = 2.47, 95% CI 1.07–5.67) were positively associated and social participation (AOR = 0.48, 95% CI 0.26–0.87) was negatively associated with persistent depressive symptoms. In addition, in univariable analysis, higher subjective economic status was negatively associated with persistent depressive symptoms (Table 3).
COR, crude odds ratio; AOR, adjusted odds ratio.
* P < 0.05, **P < 0.01.
Discussion
In this first prospective cohort study among middle-aged and older adults in Thailand, we found that the prevalence of incident depressive symptoms at 2-year follow-up was 9.8%, which is lower than the prevalence among middle-aged and older adults in China reported in a 4-year follow-up study (22.3%)Reference Wen, Liu, Liao, Yin and Wu9 and lower than cross-sectional rates of depressive symptoms (18.5–28.5%) among older adults reported in local studies in Thailand.Reference Charoensakulchai, Usawachoke, Kongbangpor, Thanavirun, Mitsiriswat and Pinijnai7,Reference Haseen and Prasartkul8 This study showed that depressive symptoms are a significant public health issue in Thailand, calling for intervention programmes to reduce the burden of depressive symptoms.
We found that lower subjective economic status, low social participation, diabetes, musculoskeletal conditions and a higher number of chronic conditions were associated with incident depressive symptoms. Low social participation, cardiovascular conditions and a higher number of chronic conditions were associated with persistent depressive symptoms. The observed associations were similar across genders, age, education, marital status and religion.
Previous researchReference Wen, Liu, Liao, Yin and Wu9,Reference Huang, Dong, Lu, Yue and Liu18 has shown, as in this study, that diabetes is associated with incident depression. This can be explained by the fact that there is currently no cure for diabetes and that individuals are required to control the condition by adhering to medication and strict diets, which in turn may lead to increased negative emotions.Reference Bi, Pei, Hao, Yao and Wang17 Consistent with previous studies,Reference Wen, Liu, Liao, Yin and Wu9,Reference Huang, Dong, Lu, Yue and Liu18–Reference Xue, Pan, Gong, Wen, Peng and Pan20 this study found an association between musculoskeletal conditions and incident depressive symptoms. Several factors may be responsible for this association, including the absence of a cure for the musculoskeletal condition, the interference of pain with daily activities, medication side-effects and shared risk factors for inflammation for both conditions.Reference Wen, Liu, Liao, Yin and Wu9
Furthermore, in line with previous studies,Reference Huang, Dong, Lu, Yue and Liu18,Reference Jiang, Zhu and Qin19,Reference Jin, Luo and He22–Reference Yang, Wang, Chiu, Wu, Handa and Liao24 we found a positive association between cardiovascular disease and persistent depressive symptoms. Previous research showed a bidirectional association between persistent depression and cardiovascular disease,Reference Hare, Toukhsati, Johansson and Jaarsma40 which may explain our findings. In univariable analysis, we also found an association between cardiovascular disease, sensory impairment and neurological (brain diseases/Alzheimer's disease) conditions and incident depressive symptoms, which is consistent with previous research.Reference Wen, Liu, Liao, Yin and Wu9,Reference Huang, Dong, Lu, Yue and Liu18,Reference Jin, Luo and He22–Reference Leung, Fan and Mahadevan26 Ageing adults with impaired vision and/or hearing may be more likely to experience functional disability and poor social support, which can lead to incident depression.Reference Huang, Dong, Lu, Yue and Liu18 In our study, ageing adults with brain diseases/Alzheimer's disease had a high prevalence of incident and persistent depressive symptoms (25.0%), which is similar to a large study among older adults in the USA, which found that at 2-year follow-up 25% of participants with dementia and 22% of those with mild cognitive impairment had developed depression.Reference Snowden, Atkins, Steinman, Bell, Bryant and Copeland25 It is suggested that depression develops as a comorbid condition during the course of dementia, necessitating integrated management of both dementia and depression.Reference Snowden, Atkins, Steinman, Bell, Bryant and Copeland25 Contrary to what was found previously,Reference Wen, Liu, Liao, Yin and Wu9,Reference Bi, Pei, Hao, Yao and Wang17–Reference Jiang, Zhu and Qin19,Reference Jia, Li, Liu, Shi, Liu and Cao21 we did not find an association between liver disease, kidney disease, lung disease, cancer and incident and persistent depressive symptoms.
In accordance with previous research,Reference Cabello, Miret, Caballero, Chatterji, Naidoo and Kowal13,Reference Bi, Pei, Hao, Yao and Wang17,Reference Chang-Quan, Xue-Mei, Bi-Rong, Zhen-Chan, Ji-Rong and Qing-Xiu27 we found an association between an increasing higher number of chronic diseases and incident and persistent depressive symptoms. Having several comorbid chronic diseases may have a negative effect on various body organs, increase symptom burden and disability, and require lifelong treatment, all of which may contribute to an increase in negative emotions, leading to incident depressive symptoms.Reference Bi, Pei, Hao, Yao and Wang17,Reference Jiang, Zhu and Qin19 This finding highlights the relevance of attending to mental health effects in diagnoses and management of multiple chronic conditions.Reference Jiang, Zhu and Qin19
Unlike some previous research,Reference Cabello, Miret, Caballero, Chatterji, Naidoo and Kowal13–Reference Luppino, de Wit, Bouvy, Stijnen, Cuijpers and Penninx16 we did not find a significant association between smoking, alcohol use, physical inactivity or body weight and incident and persistent depressive symptoms. Furthermore, we did not find significant gender and age differences in the prevalence of depressive symptoms, whereas some other studiesReference Wen, Liu, Liao, Yin and Wu9 found a preponderance of incident depressive symptoms among women and a decline with age.
Study limitations
A study limitation was the high loss to follow-up (32%). This reduced the sample of those with persistent depressive symptoms, resulting in larger confidence intervals. We lack information on survival bias and other information on participants lost to follow-up, which reduces the generalisability of the results. Furthermore, the study used a screening questionnaire for depression. Future research should at least on a subsample perform a diagnostic psychiatric evaluation. Diagnosis of depression is especially relevant in the context of comorbidity with diabetes and multi-morbidity, as there is a risk of significant diagnostic overshadowing. For example, a person with poor diabetes control may have changes in appetite, sleep and energy levels associated with hyperglycaemia, which is a further limitation of the study. The follow-up period (2 years) was relatively short and longer repeated follow-ups may be needed to identify stronger results.
Implications
Our results show the importance of baseline health status indicators in predicting longitudinal changes in depressive symptoms. Identifying individuals with the identified risk factors can help in providing early interventions to prevent the development of depression.
Data availability
The study data are publicly available from the Gateway to Global Aging Data platform: Health, Aging, and Retirement in Thailand (HART) study at https://g2aging.org/?section = study&studyid = 44. (Please note that the year for Wave 2 on the Gateway to Global Aging Data website mistakenly states '2016'; we confirm this is actually the 2017 data used in this paper.)
Acknowledgement
The Health, Aging, and Retirement in Thailand (HART) study is sponsored by Thailand Science Research and Innovation (TSRI) and National Research Council of Thailand (NRCT).
Author contributions
All three authors conceived and designed the research, performed statistical analysis, drafted the manuscript and made critical revisions of the manuscript for key intellectual content. All authors read and approved the final version of the manuscript and agreed to the authorship and order of authorship.
Funding
This research received no specific grant from any funding agency, commercial or not-for-profit sectors.
Declaration of interest
None.
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