The authors have declared that no competing interests exist.
Conceived and designed the experiments: SI TU MN YPA TI TK MI. Performed the experiments: SI TU MN YPA. Analyzed the data: FK TH SI. Contributed reagents/materials/analysis tools: SI FK. Wrote the paper: SI.
Chronic pain is recognized as a public health problem that affects the general population physically, psychologically, and socially. However, there is little knowledge about the associated factors of chronic pain, such as the influence of weather, family structure, daily exercise, and work status.
This survey had three aims: 1) to estimate the prevalence of chronic pain in Japan, 2) to analyze these associated factors, and 3) to evaluate the social burden due to chronic pain.
We conducted a cross-sectional postal survey in a sample of 6000 adults aged ≥20 years. The response rate was 43.8%.
The mean age of the respondents was 57.7 years (range 20–99 years); 39.3% met the criteria for chronic pain (lasting ≥3 months). Approximately a quarter of the respondents reported that their chronic pain was adversely influenced by bad weather and also oncoming bad weather. Risk factors for chronic pain, as determined by a logistic regression model, included being an older female, being unemployed, living alone, and no daily exercise. Individuals with chronic pain showed significantly lower quality of life and significantly higher psychological distress scores than those without chronic pain. The mean annual duration of absence from work of working-age respondents was 9.6 days (range 1–365 days).
Our findings revealed that high prevalence and severity of chronic pain, associated factors, and significant impact on quality of life in the adult Japanese population. A detailed understanding of factors associated with chronic pain is essential for establishing a management strategy for primary care.
Chronic non-cancer pain is a common problem that substantially impairs physical and psychological health and economic well-being. A number of studies in recent years have attempted to improve understanding of the various characteristics of chronic pain, including its prevalence. Previous estimates of the prevalence of chronic pain in general populations have ranged from 7% [
Although previous reports documented the clinical consequences of chronic pain, they did not explore the social consequences, such as work loss, or the negative effects of chronic pain on quality of life (QOL) and psychological well-being. To understand the various factors that may influence chronic musculoskeletal pain in a population, it is important to make comparisons within a community with similar levels of educational achievement, health awareness and social security provision, and that lives in a similar environment. A detailed understanding of the epidemiology of chronic pain is essential for efficient management of chronic pain to address its increasing social burden.
We examined the epidemiological characteristics of and influences on chronic pain in Japanese society by means of a postal survey. This cross-sectional study provided quantitative data on the prevalence and severity of various kinds of pain, the demographic characteristics of individuals with pain, the impact of pain on work, and the relationships between chronic pain, QOL and psychological distress in a community in which educational achievement, health awareness, social security provision and climate are well understood. The existence of a relationship between chronic pain and weather conditions is well known [
We performed a postal survey in the well-defined primary health care district of Owariasahi in November 2011. Owariasahi is a highly industrialized community covering an area of 21.03 km2 located in the northwest of Aichi, in the center of Honshu, Japan’s main island. The community had 82,182 inhabitants (40,321 men; 41,816 women) and 33,326 households as of January 2013, according to the Japanese Basic Resident Register Network, a national registry of Japanese citizens. Distribution of demographic characteristics in the studied population, including age, male to female ratio, and composition of economy, had no notable deviation from nationwide census data of Japan [
The survey was reviewed and approved by the Owariasahi Education and Welfare Committee and the Owariasahi municipal council on September 2011.
The questionnaire collected information on age, sex, occupation, co-residence and participation in exercise. Daily exercise was divided into three categories; “daily exercise”, “1–3 times/week” and “no regular exercise”. Participants were asked about pain intensity using an 11-point NRS (0 = no pain, 10 = worst pain imaginable), pain duration, location of pain and the perceived influence of local climate on pain symptoms.
Chronic pain was defined as a “yes” answer to the question, “Do you have any chronic pain lasting 3 months or more, either all the time or intermittently (excluding toothache, migraine, and menstrual pain)?” Participants who met these criteria were assigned to the chronic pain (CP) group. We defined severe chronic pain (severe CP) as persistent or regularly recurrent pain with a duration of >6 months and pain intensity on the NRS of ≥5. The severe CP group was included as a subset of the CP group.
Subjective QOL was assessed on the ‘EuroQol-5 Dimensions’ scale (EQ-5D) [
The Kessler 6-item psychological distress scale (K6) was also used [
To assess the social consequences of chronic pain, participants were asked to report the amount of time taken off work due to pain in the past year. Only data from participants 20–59 years old were included in this analysis, excluding students and unemployed persons. Overall work loss due to pain for the whole of Japan during 2012 was estimated on the basis of the 2012 annual report by the Japanese national tax agency, including number of employees, average working days and annual income.
Data were analyzed using SPSS version 21.0 for Windows (IBM Corp., Armonk, NY, USA). Descriptive statistics were used to present the demographic characteristics of the sample, as well as occupation, family composition, daily activity, and the location, severity and duration of chronic pain.
Continuous data are reported as the mean ± standard deviation (SD) if normally distributed, and as the median and interquartile range (IQR) if not normally distributed. Analysis of variance, Student’s unpaired t-test, and the Mann–Whitney U test were used where appropriate. Categorical data are represented as n (%), and were analyzed using Fisher’s exact test.
Simultaneous logistic regression was performed to evaluate the effect of specific demographic characteristics and social factors, as well as disease variables, on pain status. The analysis produced odds ratios and their 95% confidence intervals. P values <0.05 were considered statistically significant in all analyses.
Survey forms were completed and returned by 2,701 individuals, a response rate of 45.0%. Seventy-three respondents were excluded because of missing data, reducing the final sample size to 2,628 (43.8%). The respondents consisted of 1,104 men and 1,524 women (
All respondents (n = 2,628) | Without chronic pain (n = 1,596) | Chronic pain (n = 1,032) | Severe chronic pain (n = 456) | |
---|---|---|---|---|
M/F, n/n (%/%) | 1,104/1,524 (42.0%/58.0%) | 698/898 (43.7%/56.3%) | 406/626 (39.3%/60.7%) | 159/297 (34.9%/65.1%) |
20–30, n (%) | 185 (7.0%) | 144 (9.0%) | 41 (4.0%) | 17 (3.7%) |
31–40, n (%) | 374 (14.2%) | 263 (16.5%) | 111 (10.8%) | 46 (10.1%) |
41–50, n (%) | 345 (13.1%) | 223 (14.0%) | 122 (11.8%) | 54 (11.8%) |
51–60, n (%) | 367 (14.0%) | 201 (12.6%) | 166 (16.1%) | 77 (16.9%) |
61–70, n (%) | 673 (25.6%) | 408 (25.6%) | 265 (25.7%) | 111 (24.3%) |
71–80, n (%) | 506 (19.3%) | 270 (16.9%) | 236 (22.9%) | 111 (24.3%) |
81–90, n (%) | 159 (6.1%) | 78 (4.9%) | 81 (7.8%) | 34 (7.5%) |
91–100, n (%) | 19 (0.7%) | 9 (0.6%) | 10 (1.0%) | 6 (1.3%) |
Full-time |
810 (30.8%) | 535 (33.5%) | 275 (26.6%) | 114 (25.0%) |
Primary sector | 8 (1.0%) | 4 (0.7%) | 4 (1.5%) | 2 (1.8%) |
Secondary sector | 274 (33.8%) | 189 (35.3%) | 85 (30.9%) | 29 (25.4%) |
Tertiary sector | 528 (65.2%) | 342 (63.9%) | 186 (67.6%) | 83 (72.8%) |
Part-time | 397 (15.1%) | 253 (15.9%) | 144 (14.0%) | 57 (12.5%) |
Student | 34 (1.3%) | 29 (1.8%) | 5 (0.5%) | 2 (0.4%) |
Unemployed | 1,349 (51.3%) | 757 (47.4%) | 592 (57.4%) | 274 (60.1%) |
Unknown | 38 (1.4%) | 22 (1.4%) | 16 (1.6%) | 9 (2.0%) |
Living with ≥3 persons | 1,578 (60.0%) | 1,012 (63.4%) | 566 (54.8%) | 242 (53.1%) |
Living as a couple | 834 (31.7%) | 478 (29.9%) | 356 (34.5%) | 154 (33.8%) |
Living alone | 216 (8.2%) | 106 (6.6%) | 110 (10.7%) | 60 (13.2%) |
Daily | 622 (23.7%) | 385 (24.1%) | 237 (23.0%) | 89 (19.5%) |
1–3 days/week | 1,006 (38.3%) | 592 (37.1%) | 414 (40.1%) | 172 (37.7%) |
None | 942 (35.8%) | 586 (36.7%) | 356 (34.5%) | 187 (41.0%) |
Unknown | 58 (2.2%) | 33 (2.1%) | 25 (2.4%) | 8 (1.8%) |
3–6 months | - | 0 (0.0%) | 284 (27.5%) | 0 (0.0%) |
6–12 months | - | 0 (0.0%) | 197 (19.1%) | 111 (24.3%) |
1–3 years | - | 0 (0.0%) | 194 (18.8%) | 115 (25.2%) |
>3 years | - | 0 (0.0%) | 357 (34.6%) | 230 (50.4%) |
a Full-time workers were categorized as: primary (agriculture, forestry and fishery); secondary (mining, manufacturing and construction); or tertiary (service industries).
The criteria for chronic pain were met by 1,032 respondents, an incidence of 39.3% among all respondents; severe chronic pain was reported by 456 respondents, equating to a prevalence of 17.4%. Chronic pain was more common in women (41.1%) than men (36.8%; P <0.05). The questionnaire included employment status and family structure. Full time workers represented 30.8% of all respondents. More than half of all respondents (51.3%) were unemployed. 60% of respondents were living with three or more people, 8.2% of respondents lived alone (
The prevalence of chronic pain increased with age from 22.2% to 52.6%, roughly in proportion to age, and was highest among patients in their nineties (
Among the 1,032 respondents with chronic pain, the mean severity on an 11-point NRS was 5.2 ± standard deviation 2.3, and 607 (58.5%) reported a pain intensity of 5 or more.
The mean severity of pain in the chronic pain (CP) group was 5.2 ± 2.3. The severe CP group had an average pain severity of 6.7 ± 1.5. The most common location of pain (one answer was allowed) was the lower back (30.6%) followed by the knees (19.8%), shoulders (17.0%) and neck (8.3%). Almost 40% of respondents had chronic spinal problems, including neck, middle back, and lower back pain, with more men reporting low back pain and more women reporting neck pain.
When asked under what conditions their chronic pain worsened or improved (
Chronic pain | Severe chronic pain | |||||
---|---|---|---|---|---|---|
Better | Worse | No Change | Better | Worse | No Change | |
n (%) | n (%) | n (%) | n (%) | n (%) | n (%) | |
At rest | 498 (62.4%) | 46 (5.8%) | 254 (31.8%) | 214 (60.5%) | 23 (6.5%) | 117 (33.1%) |
During activity | 77 (9.9%) | 378 (48.8%) | 319 (41.2%) | 26 (7.3%) | 200 (56.3%) | 129 (36.3%) |
Oncoming bad weather | 36 (5.1%) | 168 (23.7%) | 505 (71.2%) | 7 (2.2%) | 94 (29.8%) | 214 (67.9%) |
During bad weather | 0.7% (5) | 171 (24.9%) | 512 (74.4%) | 0 (0.0%) | 100 (31.8%) | 214 (68.2%) |
Cold conditions | 4.4% (33) | 348 (46.9%) | 361 (48.7%) | 5 (1.5%) | 185 (55.6%) | 143 (42.9%) |
Warm conditions | 45.2% (327) | 19 (2.6%) | 378 (52.2%) | 137 (43.1%) | 15 (4.7%) | 166 (52.2%) |
Variations in the total number are a consequence of missing values.
The epidemiological data of Owariasahi city in 2011 was as follows: mean temperature 16.1°C (min -3.2°C, max 36.7), mean humidity 67%, mean annual precipitation 1,785.5 mm, mean annual air pressure 1,008.1Pa, and annual total sunshine 2,151.5 hours.
The questionnaire also obtained information about daily exercise: 23.7% of respondents reported they exercised daily, 29.5% exercised 1–3 times a week, and the remaining 44.6% did no regular exercise. The daily exercise group reported a lower frequency of severe chronic pain (14.3%) than the groups that reported exercising 1–3 times/week (17.1%) or no regular exercise (19.9%; P<0.001).
Individuals with chronic pain showed significantly lower utility values on the EQ-5D and higher K6 scores than those without chronic pain (
Statistical analysis undertaken with independent
The severe CP group had very low QOL scores (0.73± 0.17) and high K6 scores; the CP group’s K6 mean was 5.2 ± 5.2, which is above the threshold of 5 for anxiety disorder. Complaints of chronic pain were more frequent in the group that did not exercise than in the group who exercised every day, and their QOL was also low (0.75 ± 0.20 compared with 0.80 ± 0.18).
Logistic regression analysis was undertaken to obtain a subset of sociodemographic variables associated with chronic pain and severe chronic pain (
Chronic pain (vs. without chronic pain) | Severe chronic pain (vs. without chronic pain) | |||||
---|---|---|---|---|---|---|
OR | 95%CI | P-value | OR | 95%CI | P-value | |
Female (vs, male)* | 1.304 | 1.108–1.534 | 0.001 | 1.621 | 1.299–2.023 | <0.001 |
Age (per 1 year old) | 1.019 | 1.014–1.024 | <0.001 | 1.022 | 1.015–1.029 | <0.001 |
Age-group (years)♯ | ||||||
20–30 (n) | 1.000 | ref | 1.000 | ref | ||
31–40 (n) | 1.471 | 0.974–2.221 | 0.067 | 1.482 | 0.819–2.684 | 0.194 |
41–50 (n) | 1.939 | 1.285–2.927 | 0.002 | 2.125 | 1.183–3.817 | 0.012 |
51–60 (n) | 2.921 | 1.950–4.374 | <0.001 | 3.368 | 1.907–5.950 | <0.001 |
61–70 (n) | 2.349 | 1.605–3.438 | <0.001 | 2.478 | 1.434–4.283 | 0.001 |
71–80 (n) | 3.180 | 2.153–4.695 | <0.001 | 3.795 | 2.185–6.591 | <0.001 |
81–90 (n) | 3.833 | 2.401–6.120 | <0.001 | 4.183 | 2.185–8.007 | <0.001 |
91–100 (n) | 4.094 | 1.556–10.772 | 0.002 | 6.343 | 1.994–20.174 | 0.002 |
Occupation† | ||||||
Full-time | 1.000 | ref | 1.000 | ref | ||
Part-time | 0.933 | 0.714–1.219 | 0.61 | 0.808 | 0.557–1.172 | 0.261 |
Student | 0.490 | 0.185–1.297 | 0.151 | 0.464 | 0.107–2.009 | 0.305 |
Unemployed | 1.014 | 0.807–1.274 | 0.904 | 1.044 | 0.769–1.418 | 0.782 |
Family composition† | ||||||
Living with ≥3 persons | 1.000 | ref | 1.000 | ref | ||
Living in a couple | 1.080 | 0.902–1.294 | 0.401 | 1.086 | 0.855–1.381 | 0.499 |
Living alone | 1.442 | 1.067–1.947 | 0.017 | 1.763 | 1.221–2.547 | 0.003 |
Daily exercise† | ||||||
Daily | 1.000 | ref | 1.000 | ref | ||
1–3 days/week | 1.237 | 1.004–1.525 | 0.046 | 1.384 | 1.034–1.853 | 0.029 |
None | 1.179 | 0.949–1.465 | 0.137 | 1.701 | 1.267–2.282 | <0.001 |
EQ-5D† | ||||||
Value (per 0.1) | 0.464 | 0.435–0.496 | <0.001 | 0.403 | 0.368–0.440 | <0.001 |
K6† | ||||||
K6 point (per 1) | 1.113 | 1.087–1.139 | <0.001 | 1.158 | 1.126–1.191 | <0.001 |
Abbreviations: OR: odds ratio; 95%CI, 95% confidence interval; ref, reference category.
Odds ratios were adjusted for age*, sex♯ or both†.
Finally, we analyzed absence from work caused by chronic pain. Among the 1,221 respondents aged 20–59 years (excluding unemployed persons and students),
Number of days off work | Chronic pain | Severe CP | ||
---|---|---|---|---|
Number of respondents |
% | Number of respondentsa | % | |
1 day | 61 | 38.1% | 21 | 28.4% |
2 days | 29 | 18.1% | 10 | 13.5% |
3 days | 13 | 8.1% | 5 | 6.8% |
4–6 days | 14 | 8.8% | 9 | 12.2% |
1 week | 6 | 3.8% | 5 | 6.8% |
~2 weeks | 10 | 6.3% | 8 | 10.8% |
~1 month | 12 | 7.5% | 9 | 12.2% |
~3 months | 8 | 5.0% | 4 | 5.4% |
~1 year | 7 | 4.4% | 3 | 4.1% |
Total | 160 | 100.0% | 74 | 100.0% |
Days off work (mean ± standard deviation) | 17.2 ± 54.0 | 20.5 ± 60.6 | ||
Total days off work | 2,752 | 1,518 |
aStudents, the unemployed, and those over the age of 60 were excluded from the analysis.
We determined the extent and impact of chronic pain on a general population in Japan.
A large number of epidemiological investigations of chronic pain have recently been published (
Author | Published | Country | Survey method | Participants | Response rate | Age | Prevalence | Definition of Chronic Pain | |
---|---|---|---|---|---|---|---|---|---|
Duration (months) | Pain Severity | ||||||||
Crook J et al. [ |
1984 | Canada | Telephone | 827 | unknown | ≥18 | 16% | – | – |
Bowsher D et al. [ |
1991 | UK | Telephone | 2,942 | unknown | ≥15 | 7% | 3 | – |
Croft P et al. [ |
1993 | UK | Postal | 1340 | 75% | 18–85 | 35% | 3 | – |
Andersson HI et al. [ |
1993 | Sweden | Postal | 1806 | 90% | 25–74 | 55.2% | 3 | – |
Elliott AM et al. [ |
1999 | UK | Postal | 3065 | 82.3% | ≥25 | 50.4% | 3 | – |
Blyth FM et al. [ |
2001 | Australia | Telephone | 17,543 | 70.8% | ≥16 | 18.6% | 3 | – |
Catala E et al. [ |
2002 | Spain | Telephone | 5,000 | 42% | 18–95 | 23.4% | 3 | – |
Ng KF et al. [ |
2002 | China | Telephone | 1,051 | 47.7% | ≥18 | 10.8% | 3 | – |
Rustøen T et al. [ |
2004 | Norway | Postal | 1,912 | 48.5% | 19–81 | 24.4% | 3 | – |
Breivik H et al. [ |
2006 | Europe | Telephone | 46,394 | 54% | ≥18 | 19% | 6 | ≥5 |
Moulin DE et al. [ |
2007 | Canada | Telephone | 2,012 | 19.1% | 18–75 | 29% | 6 | – |
Neville A et al. [ |
2008 | Israel | Telephone | 3,738 | 92% | ≥25 | 46% | 3 | – |
Sá KN et al. [ |
2008 | Brazil | Interview | 2,297 | 97.1% | ≥20 | 41.4% | 6 | – |
Yeo SN et al. [ |
2009 | Singapore | Telephone | 4,141 | 43.6% | 18–85 | 8.7% | 3 | ≥4 |
Johannes CB et al. [ |
2010 | USA | Internet | 27,035 | 75.7% | ≥18 | 30.7% | 6 | – |
Toblin RL et al. [ |
2011 | USA | Telephone | 4,090 | 62% | ≥18 | 26.0% | – |
– |
Raftery MN et al. [ |
2011 | Ireland | Postal | 1,204 | 38% | ≥18 | 36% | 3 | – |
Nakamura M et al. [ |
2011 | Japan | Postal | 11,507 | 60% | ≥18 | 15.4% | 6 | ≥5 |
Azevedo LF et al. [ |
2012 | Portugal | Telephone | 5,094 | 76% | ≥18 | 36.7% | 3 | – |
Kurita, GP et al. [ |
2012 | Denmark | Post or Internet | 14,925 | 60.7% | ≥16 | 26.8% | 6 | – |
Shibata, M et al. [ |
2014 | Japan | Interview | 927 | 46% | ≥40 | 47% | 6 | – |
A dash (–) indicates no limitation.
a Respondents answered “yes” to the question, “Do you suffer from any type of chronic pain, that is, pain that occurs constantly or flairs up frequently?”
According to the definition of chronic pain offered by IASP, “chronic pain is pain that persists beyond normal tissue healing time, which is assumed to be 3 months”. The median prevalence of chronic pain in the 14 studies that used this definition in adults was 29.1%, in our population it was 39.3%—suggesting that approximately 22 million people in Japan suffer from chronic pain to some extent. In contrast, Breivik et al. [
Those reporting chronic pain in our study were more likely to be depressed and have low QOL. Becker et al. [
The weighting of the EQ-5D varies by country; therefore, it is necessary to compare our results to other EQ-5D studies in Japan. We found that the utility value of respondents with severe chronic pain was 0.73, which is lower than that of patients with chronic renal failure (0.798) [
Value set | Status | N | Author | Published |
---|---|---|---|---|
1 | Full health | |||
0.846 | Diabetes mellitus type 2 | 220 | Sakamaki H. et al. [ |
2006 |
0.808 | Asthma | 54 | Oga T. et al. [ |
2003 |
0.798 | Chronic renal failure | 71 | Tajima R. et al. [ |
2010 |
0.75 | Chronic schizophrenia | 47 | Nakamae T. et al. [ |
2010 |
0.665 | Dementia, Alzheimer type | 72 | Hachimori A. et al. [ |
2009 |
0.49 | Arteriosclerosis obliterans (critical limb ischemia) | 289 | Aramoto H. et al. [ |
2003 |
0.37 | Destructive spondyloarthritis with rheumatoid arthritis | 25 | Uehara M. et al. [ |
2012 |
0 | Death |
The reported K6 scores also showed that there is a high burden of mood disorder among those with chronic pain: the mean K6 score in the severe CP group was 5.2; a K6 score over 5 points is considered to indicate mood disorder in the Japanese population [
Many patients with chronic pain complain that their condition is aggravated by changes in the weather [
Interesting relationships between chronic pain and family structure were observed. Previous studies have reported that individuals living alone, or who are divorced, have a higher prevalence of musculoskeletal pain [
In the United States, an average of 5.2 hours/week of productive time was lost due to musculoskeletal pain [
The limitation of this study was the relatively low response rate (43.8%), which may have influenced the prevalence rate of chronic pain that we report. As shown in
We focused on the relationship between chronic pain and the climate or environmental situation in this study. We did not measure or quantify these kinds of environmental factors because the respondents did not recognize precise atmospheric pressure or temperature. However, almost half of respondents believe their pain to be related to some kind of environmental factor. Our data imply that the further investigation of sensory information from the point of view of environmental conditions may provide us with a new approach to overcoming formidable chronic pain.
We found that the prevalence of chronic pain was approximately 40% in a general Japanese population. Chronic pain has a significant impact on occupational and daily social life, and seriously affects psychological health. As the population of Japan ages, it is important to recognize that chronic pain is a serious social issue, which should be addressed by the entire Japanese society. Specific and effective interventions are needed to reduce the prevalence of musculoskeletal pain and its debilitating effects. Apart from the physical disabilities associated with chronic pain, our findings show that chronic pain is associated with mental health issues, decreased QOL and social loss due to absence from work. Our data provide a scientific basis for estimating the burden of chronic pain in Japanese communities. National countermeasures are required to address chronic pain, including the promotion of daily exercise habits to address persistent musculoskeletal pain.
(TIF)