Chronic Pain and Poor Self-rated Health

Context Chronic pain is common in Western societies. Self-rated health is an important indicator of morbidity and mortality, but little is known about the relation between chronic pain and self-rated health in the general population.

Objective To analyze the association between chronic pain and self-rated health.

Design, Setting, and Population A questionnaire survey carried out during the spring of 2002 of an age- and sex-stratified population sample of 6500 individuals in Finland aged 15 to 74 years, with a response rate of 71% (N = 4542) after exclusion of those with unobtainable data (n = 38). Chronic pain was defined as pain with a duration of at least 3 months and was graded by frequency: (1) at most once a week; (2) several times a week; and (3) daily or continuously. On the basis of a 5-item questionnaire on self-rated health, individuals were classified as having good, moderate, or poor health. Multinominal logistic regression analysis was used to assess the determinants of health. Analysis included sex, age, education, working status, chronic diseases, and mood.

Main Outcome Measures Perceived chronic pain graded by frequency and self-rated health status.

Results The prevalence of any chronic pain was 35.1%; that of daily chronic pain, 14.3%. The prevalence of moderate self-rated health was 26.6% and of poor health, 7.6%. For moderate self-rated health among individuals having chronic pain at most once a week compared with individuals having no chronic pain, the adjusted odds were 1.36 (95% confidence interval [CI], 1.05-1.76); several times a week, 2.41 (95% CI, 1.94-3.00); and daily, 3.69 (95% CI, 2.97-4.59). Odds for poor self-rated health were as follows: having chronic pain at most once a week, 1.16 (95% CI, 0.65-2.07); several times a week, 2.62 (95% CI, 1.76-3.90); and daily, 11.82 (95% CI, 8.67-16.10).

Conclusion Chronic pain is independently related to low self-rated health in the general population.

Pain is associated with many health problems and disturbed functioning^1-6 and is a common reason for seeking medical care.^7-10 In Finland, for example, 40% of visits to primary care physicians are due to pain.⁹ Chronic pain is expensive, mainly because of the resulting disability and absence from work.^11-14 Studies throughout the past 2 decades have shown a large variability of prevalence rates of pain. According to 1 comprehensive review, the prevalence of chronic benign pain varies between 2% and 40%, according to the method used in the study and the populations studied.¹⁵

In recent studies, more attention has been paid to the impact of chronic pain on daily living. In an epidemiologic questionnaire study in Scotland, the prevalence of significant chronic pain was 14.1%.^6,16 Chronic pain was defined as "continuous or intermittent pain or discomfort which has persisted for at least 3 months, and for which painkillers have been taken and treatment sought recently and frequently." Among an Australian adult population, 17% of men and 20% of women reported daily chronic pain.⁵ For chronic pain that interferes with daily life, the corresponding percentages were 11% and 13.5%.⁵

Self-rated health is an independent predictor of mortality.¹⁷ Factors related to illness, such as chronic diseases and various symptoms, are also related to health.^18,19 Low general health has been found to relate to poor recovery from chronic pain.²⁰ Among home-dwelling elderly individuals, daily pain is related to poor health.²¹ However, to the authors' knowledge, no previous population-based studies have focused on whether there is a particular relationship between self-rated health and chronic pain in a general population.

To analyze the prevalence of chronic pain and its impact on self-rated health, we performed a population-based study of individuals aged 15 to 74 years in Finland.

This population survey was carried out during the spring of 2002. The 5.2 million inhabitants of Finland are primarily concentrated in southern Finland and in several larger cities in the rest of the country. Of the citizens aged 15 to 74 years, 60% are educated beyond primary school level (9 years). A total of 25% are retired. Disability pension is received by 5% of the population. In 2002, the unemployment rate among the population aged 15 to 74 years was 9%, and the gross national product per inhabitant was US $25 000.²² In Finland, primary health care is provided mainly in primary health care centers, which are accessible to everyone for ambulatory medical services at a cost of US $30 per year and financed mainly by taxes. In addition, outpatient visits are made to occupational health care centers or the private health care sector.²³

The questionnaire was mailed to a random sample of 6500 people aged 15 to 74 years and living in Finland. The sample was stratified by sex and age to ensure a sufficient number of responses from all ages. Both sexes were divided into 12 age groups in 5-year periods, from 15 to 74 years, and these 24 subgroups each contained 270 or 271 individuals. The home addresses of the individuals were obtained from the Finnish Population Register Center. The random sampling and stratification was conducted by the Finnish Population Register Center from its database, which includes everyone living permanently in Finland. Two reminders were sent to the individuals. The questionnaires were available in Finnish and Swedish, both of which are official languages in Finland; everyone living permanently in Finland speaks one or both. The 4-page form contained questions about pain experienced during the past 7 days, localization of the pain, duration and frequency of pain symptoms, chronic illnesses, mood, and perceived health.

To detect individuals with pain and to grade chronic pain, 3 structured questions were used: experience of pain during the preceding week, duration of pain, and frequency of pain. In defining duration and frequency of pain, we used the same method as used in our previous study of primary care patients,⁹ and the same kinds of methods have been widely used in other epidemiologic studies^5,8,16 and in clinical settings. Individuals who had experienced pain during the preceding week were classified as individuals with pain. Chronic pain was defined as pain lasting for at least 3 months. We graded chronic pain by frequency: 0, no chronic pain; 1, at most once a week; 2, several times a week; and 3, daily or continuously.

In assessing self-rated health, we used the same self-rated items as in the Finnish Health Care Survey 1995/96.²⁴ Equivalent items have been used in several other studies.^17-19,21 Individuals were asked to grade their health as good (1), quite good (2), moderate (3), rather poor (4), or poor (5). As in the Finnish Health Care Survey, individuals reporting good or quite good health were classified as having good health, and those reporting rather poor or poor health were classified as having poor health.

Individuals who were working, in school, or caring for children at home were classified as working; individuals who were on sick leave, were unemployed, or were retired were classified as not working. Individuals with more than 9 years of education were classified as having education beyond primary school. Age was used as a continuous covariate in logistic regression analysis.

Assessment of chronic disease prevalence was based on reports of disease number codes in the individuals' personal Sickness Insurance Card. The Social Insurance Institution of Finland provides reimbursement for treatment of 44 chronic diseases for which drug treatment is necessary to maintain the patient's health. This reimbursement system covers all permanent residents of Finland, regardless of age, monetary status, or address.²⁵ The diseases are marked with special disease number codes in the personal Sickness Insurance Card (for example, there are disease codes for hypertension, coronary heart disease, diabetes, asthma, rheumatoid arthritis, and gout). To obtain reimbursement, the patient must first obtain a certificate from his or her physician to confirm the nature of the illness and the need for medication. Thus, this system comprehensively covers general chronic morbidity in Finland. To assess morbidity, the presence of chronic illness was graded: no chronic disease, 1 chronic disease, or 2 or more chronic diseases. In addition to these defined and diagnosed chronic diseases, the presence of other chronic conditions was determined. Thus, the prevalence of fibromyalgia, chronic back diseases, osteoarthritis, and migraine could be assessed, all of which have pain as a most important symptom.

The questionnaire included a self-completed screening instrument for depression, the Depression Scale (DEPS).²⁶ DEPS was developed for detecting depressive symptoms and screening individuals with possible clinical depression from community samples. DEPS is validated and has been found to be suitable for screening depression in the general population. It includes 10 questions rated from 0 to 3.^26,27 In the screening, a DEPS score of more than 8 has been regarded as signaling a possible depression. Mood was dichotomized according to DEPS score.

The total prevalence of chronic conditions was standardized to correspond to the real age and sex distribution of the Finnish population. The weighting provided by the Finnish Population Register Center was used. Cross-tabulation was used to describe self-rated health in groups defined by chronic pain, sex, education, working status, mood, and chronic diseases. According to previous studies, the prevalence of chronic pain,^15,16 chronic diseases,²⁴ and low self-rated health¹⁸ is higher among older individuals than among younger ones. The cross-tabulation was therefore conducted separately for 2 age groups (aged 15-44 years and 45-74 years) to assess the impact of age on self-rated health in defined groups.

Individuals with moderate or poor self-rated health were compared with those with good self-rated health. Multinomial logistic regression analysis was used to control for the potentially confounding effect of age (as a continuous covariate) and other covariates (including sex, education, working status, and chronic diseases and mood), although these variables are known to relate to self-rated health.^17-19,21 In addition to odds ratios (ORs), results of a likelihood ratio test were reported to assess the model. Collinearity statistics were used to assess the possible collinearity between covariates. Possible overfitting was assessed by comparing regression coefficients (β) and their SE between univariate and multivariate analysis. The impact of missing values on the results of multinomial logistic regression analysis was assessed by replacing them with mode values. The multinomial logistic regression analysis was conducted for the total sample and separately for individuals aged 15 to 44 years and individuals 45 to 74 years. In addition, analysis was conducted stratified by chronic diseases. Statistical software (SPSS version 9.0.1; SPSS Inc, Chicago, Ill) was used in data analysis. P<.05 was regarded as significant.

Sixty-eight questionnaires did not reach the recipients for various reasons (eg, the intended recipient was traveling, addresses were wrong, death), or recipients were excluded because of dementia, retardation, or autism. A total of 4542 of the remaining 6432 questionnaires were returned (response rate, 71%). The respondents were from 5 mainland counties of Finland: Southern, 39.3% (the real proportion of the population in that area is 40.3%); Western, 35.5% (35.5%); Eastern, 12.8% (11.3%); Oulu, 8.4% (8.8%); and Lapland, 3.7% (3.6%).

The proportion of female respondents was 55%. The mean age of respondents was 47 years and median age 48 years; 48.9% were employed, 11.3% were in school or at home with children, 9.1% were unemployed, 1.3% were on sick leave, and 29.4% were retired. Thus, almost 40% were not working (Table 1). Almost two thirds had been educated beyond primary school (9 years). A total of 23.4% of all the study individuals had some chronic disease, and of these, about half had at least 2 chronic diseases. The most common chronic diseases were hypertension (n = 474; age-standardized prevalence, 8.2%), coronary heart disease (n = 200; age-standardized prevalence, 2.9%), asthma (n = 160; age-standardized prevalence, 2.9%), and diabetes (n = 125; age-standardized prevalence, 2.5%).

The age-standardized prevalence of any chronic pain was 35.1%. In general, chronic pain was as common in men as in women. Among all respondents, the older the respondents, the higher the prevalence of chronic pain (Figure 1). Of individuals with chronic pain, 45% had daily or continuous pain. The age-standardized prevalence of daily pain was 14.3%. The prevalence rates of daily pain increased clearly at age 40 years. The prevalence of chronic pain did not vary markedly by geographic location.

Self-rated health was reported by 4485 individuals (99% of individuals). The age-standardized prevalence for moderate self-rated health was 26.6%; for poor health, 7.6%. Moderate and poor health was more common among older individuals (Figure 2). Table 2 shows the self-rated health in different groups. Prevalence rates of moderate and poor health increased with frequency of pain relatively more among younger individuals than older ones. In general, the prevalence of poor health among individuals with chronic daily pain was 8-fold higher than in those with nochronic pain. Men rated their health as moderate or poor slightly more commonly than women. Individuals with higher education rated their health as better than that of individuals with at most 9 years' education, and this trend seemed to be clearer among individuals aged 45 years and older. Having chronic disease was associated with poor self-rated health. Individuals with an elevated DEPS score (low mood) had poor self-rated health more often than individuals with normal mood. The self-rated health did not vary by main geographic locations. A total of 12.2% of the respondents reported daily pain related to moderate or worse health (age-standardized prevalence, 10.4%).

In the model used in the logistic multinomial regression analysis for all individuals, the likelihood ratio test showed a significance level of P<.001 for the association of self-rated health and all the covariates except sex (P = .08). When assessed for different levels of self-rated health, sex was statistically significantly associated with poor health (P = .03). No significant collinearity between covariates was found. In this model, there was no significant overfitting in general, although for chronic diseases there was a considerable difference between unadjusted and adjusted coefficients and between ORs. For moderate health and 1 chronic disease, the unadjusted β (SE) was 0.98 (0.09); adjusted, 0.50 (0.10). For 2 or more chronic diseases, unadjusted β (SE) was 1.77 (0.14); adjusted, 0.92 (0.16). Corresponding values for poor health and 1 chronic disease were unadjusted β (SE), 1.65 (0.13); adjusted, 1.06 (0.16); and for 2 or more chronic diseases, unadjusted, 2.72 (0.17); adjusted, 1.67 (0.21). Replacing missing values with mode values of covariates had no impact on results.

Table 3 shows the unadjusted and adjusted ORs obtained from logistic regression analysis in which moderate and poor health were compared with the designated reference variable in each category among all individuals. All covariates were associated with moderate self-rated health. With poor health, daily or continuous chronic pain (unadjusted OR, 22.69; 95% confidence interval [CI], 17.24-29.87), having 2 or more chronic diseases (unadjusted OR, 15.16; 95% CI, 10.88-21.12), and having elevated DEPS score (unadjusted OR, 12.12; 95% CI, 9.57-15.32) had the strongest unadjusted associations. Having more than 9 years of education and working were inversely associated with poor health. In multivariate analysis, all covariates except sex were associated with moderate self-rated health, and daily or continuous pain had the strongest association (adjusted OR, 3.69; 95% CI, 2.97-4.59). The association between chronic pain and poor self-rated health increased with pain frequency: the adjusted OR was 12-fold higher (adjusted OR, 11.82; 95% CI, 8.67-16.10) in individuals who experienced daily pain than in individuals without chronic pain. Elevated DEPS score (adjusted OR, 10.43; 95% CI, 7.97-13.67) was strongly associated with self-rated poor health. A significant association between chronic disease and poor health increased with the number of diseases (2 or more chronic diseases: adjusted OR, 5.23; 95% CI, 3.47-7.90). Higher educational status and being employed were inversely associated with poor health, as was female sex.

Table 4 shows the results of multinomial logistic regression analysis stratified by age (15-44 years; 45-74 years), including all covariates. In older individuals, frequent pain and chronic diseases did not reach as strong an association with moderate health as they did in younger individuals, although CIs for ORs were narrower among older individuals. Among individuals aged 15 to 44 years, frequent pain and chronic diseases associated strongly with poor health: CIs were large. In older individuals, chronic daily pain associated with poor health nearly as strongly as among younger persons, CIs being narrower among older individuals. Chronic diseases associated less strongly with poor health in older individuals than in younger ones. Elevated DEPS score had stronger association with poor health among older individuals than among individuals aged 15 to 44 years. According to the likelihood ratio test, sex (P = .48) and educational level (P = .30) were not associated with self-rated health among individuals aged 15 to 44 years. Among older individuals, age (P = .18) and sex (P = .095) were not associated with differences in self-rated health.

In an analysis conducted separately for individuals without and those with chronic disease, an association between self-rated health and daily chronic pain was found in both cases. For individuals without chronic disease and who experienced daily pain, adjusted OR for moderate self-rated health was 3.45 (95% CI, 2.68-4.45); for poor health, 11.28 (95% CI, 7.56-16.81). In individuals with chronic disease, the corresponding OR for moderate health was 4.35 (95% CI, 2.80-6.77); for poor health, 13.81 (95% CI, 8.09-23.56).

The definition of chronic disease in the present study included rheumatoid arthritis (n = 64) and gout (n = 17), which are covered by the Finnish reimbursement system. If these were not included in chronic diseases, the adjusted OR of daily chronic pain for moderate self-rated health was 3.71 (95% CI, 2.99-4.61) and for poor health was 11.93 (95% CI, 8.76-16.26). Our definition of chronic diseases did not include fibromyalgia (n = 40), osteoarthritis (n = 105), chronic back diseases (n = 110), or migraine (n = 46). Of the individuals with these painful conditions (with rheumatoid arthritis and gout, in total n = 349), a total of 70.8% had chronic pain, and 44.4% had chronic daily pain. A third (33.4%) of these individuals rated their health poor (vs 6.6% of the individuals without painful conditions). If these painful conditions were included as chronic diseases, adjusted OR of daily chronic pain for moderate self-rated health was 3.55 (95% CI, 2.85-4.42); for poor health, 10.56 (95% CI, 7.72-14.45). If these painful conditions were included in analysis as a separate covariate, the adjusted OR of chronic painful conditions for moderate self-rated health was 2.35 (95% CI, 1.72-3.20) and for poor health, 5.26 (95% CI, 3.58-7.71). Adjusted OR of daily chronic pain for moderate self-rated health was 3.48 (95% CI, 2.80-4.34); for poor health, 9.84 (95% CI, 7.17-13.50). After exclusion of individuals with these disorders from the analysis, the corresponding values of daily chronic pain for moderate health were OR, 3.66 (95% CI, 2.91-4.61); for poor health, OR, 10.14 (95% CI, 7.19-14.30).

In this study, chronic pain was related to impaired self-rated health. The association between chronic pain and low self-rated health increased with frequency of pain and worsening of self-rated health. Daily chronic pain seemed to relate to poor health even more strongly than chronic diseases or age. A considerable proportion of the study population had frequent or persistent chronic pain. This study indicates that 1 of 7 adults in Finland has daily chronic pain. The prevalence of daily pain increased with age, as did the prevalence of self-rated moderate or poor health. On the basis of these results, 1 of 10 adults has daily pain related to not better than moderate perceived health.

The findings of chronic pain prevalence are in line with those of previous studies.^5,6,16 The stratified sample of the nationwide study was drawn randomly from the Finnish population. The response rate was good, increasing with age and being better among women than men. The prevalence of pain increased with age, which might be one reason why younger individuals' interest in responding was not as high as that of older individuals. It was not possible to obtain any information other than age and sex of nonparticipants.

Contrary to findings in some previous studies,^5,8,16 women did not have chronic pain more often than men did. The reason for this discrepancy is unclear. In this study, men's response rate was slightly lower than women's, which may partly explain the absence of expected sex difference. On the other hand, Finnish women use health services more actively than men,²⁴ which might be one reason for this finding. The assumption, however, is that in Finland there is not a remarkable sex difference in overall prevalence of chronic pain.

In the Finnish Health Care Survey,²⁴ 11% of the study population reported poor health, which is more than in this study. This difference is probably due to different methods: the Finnish Health Care Survey was an interview study of households, with a response rate of 88%. It is likely that in the present survey, individuals with the most deteriorated health did not respond as well as they did in the Finnish Health Care Survey. The prevalence of chronic diseases in this study was not as high as that shown by the statistics of the Social Insurance Institution. For example, for the most common chronic diseases (hypertension, asthma, coronary heart disease, and diabetes) the reported prevalence rates were 9.1% (8.2% in this study), 3.8% (2.9%), 3.6% (2.9%), and 2.7% (2.5%). Our study comprised individuals aged 15 to 74 years, whereas the statistics of the Social Insurance Institution included all ages. The prevalence of chronic diseases reported in this study seems to be reliable. However, it is possible that individuals with more severe morbidity were underrepresented, which could have reduced the effect of chronic diseases on self-rated health. In general, because of the high response rate and large number of respondents, the results of this study can be generalized to the Finnish adult population.

Frequent chronic pain and chronic diseases had a bigger impact on self-rated health among young individuals than among older ones, although CIs for ORs were larger in younger than in older individuals. As assessed stratified by age, subgroup sizes were small for some covariates, especially among younger individuals, which resulted in larger CIs; results should be considered with caution, although their trends seemed to be logical and reliable. Absolute prevalence rates of low self-rated health, chronic pain, and chronic diseases were higher among older individuals. In a previous study of individuals aged 70 years and older, pain was found to be more strongly associated with any daily pain than with chronic diseases,²¹ as was the case in the adult population of the present study. In this study, however, the association with pain was stronger, which is probably due to the different ages of respondents and the definition of pain. Instead of any daily pain, our definition included chronicity and persistence of pain. Health-deteriorating factors accumulate among older individuals, and a single factor does not reach as high a relative importance as it does among younger individuals. Education played a more important role among older individuals than among individuals younger than 45 years, which is understandable because a higher proportion of older citizens are less educated than younger ones.

To assess the clinical significance of chronic pain, pain was graded by frequency. In a large Canadian survey,¹⁸ moderate or severe pain related to good (vs excellent) and poor (vs excellent) self-rated health, but that relation was not as strong as the association between daily pain and self-rated poor health in the present study. In the Canadian study, pain was graded by neither duration nor frequency. Other significantly associated factors in the Canadian study included chronic conditions, older age, low educational level, not being in the labor force, and female sex (inverse association). In our study, female sex was inversely associated with poor health among older individuals but not among younger ones. The covariates used in the logistic regression analysis of the present study seemed to explain well the self-rated health.

The chronic diseases reported in this study did not include many chronic conditions that have pain as their dominant symptom. This assessment of chronic morbidity was based on diagnosed diseases. The most common chronic diseases in the study were cardiovascular diseases, diabetes, and asthma, which are related to poor perceived health but do not have pain as their principal symptom. Comparison of ORs indicates that association between self-rated health and chronic diseases was weaker in multivariate analysis than in univariate analysis. Also, association between chronic pain and health was weaker in the multivariate analysis. It is reasonable to keep these chronic diseases and chronic pain in the same regression model when assessing their impact on self-rated health. However, we also conducted analyses separately for individuals without and those with chronic disease. Regardless of the presence or absence of chronic diseases, chronic daily pain was strongly associated with worsened self-rated health. Among individuals with painful disorders such as fibromyalgia, osteoarthritis, migraine, and chronic back diseases, distinguishing the effect of pain from the effect of the diagnosis itself could have been impossible. However, regardless of inclusion or exclusion of these chronic disorders, chronic daily pain was independently associated with moderate and poor health. These results strengthen the assumption that frequent chronic pain independently and even more strongly than chronic diseases in general affects self-rated health. It is evident, however, that chronic pain in this study, as well as in previous studies, also appears to be an indicator of general morbidity. In general, the present findings about the relation between chronic diseases and self-rated health are consistent with those of other recently published studies.^18,19,21

Depressive symptoms and clinical depression are known to be associated with chronic pain^28-30 and self-rated health.^18,19,21 It is not known yet whether depression is antecedent or consequent to chronic pain. There is some evidence that depression could more often be a consequence of pain.^29,30 A recent study suggested that the presence of chronic painful physical conditions increases the duration of depression, and co-occurrence of chronic pain and nonpainful medical conditions increases the likelihood of depression.³⁰ It is possible that a considerable proportion of respondents with an elevated depression score in this study had depressive symptoms as a consequence of chronic pain. However, because mood is independently related to self-rated health, it was reasonable to keep mood in the analysis as a confounding variable.

In conclusion, daily chronic pain is common in the general population of Finland, and chronic pain is independently and significantly related to self-rated health. These findings support the view that chronic daily pain is a dominant manifestation of chronic morbidity or even a chronic disease by definition, which emphasizes the importance of the management and prevention of chronic pain. More attention should be paid in clinical practice to the detection, assessment, and treatment of pain. At the community or society level, pain management and prevention should be implemented in health-promotion strategies.