Abstract

Introduction

Chronic back problems may not be potentially fatal, but they are an important public health ¹1. Andersson GB. Epidemiological features of chronic low-back pain. Lancet 1999; 354:581-5.^,22. Dionne CE, Dunn KM, Croft PR. Does back pain prevalence really decrease with increasing age? A systematic review. Age Ageing 2006; 35:229-34.^,33. Hoy D, Brooks P, Blyth F, Buchbinder R. The epidemiology of low back pain. Best Pract Res Clin Rheumatol 2010; 24:769-81., economic, and social problem ⁴4. Dagenais S, Caro J, Haldeman S. A systematic review of low back pain cost of illness studies in the United States and internationally. Spine J 2008; 8:8-20.^,55. Deyo RA, Cherkin D, Conrad D, Volinn E. Cost, controversy, crisis: low back pain and the health of the public. Annu Rev Public Health 1991; 12:141-56.. Chronic back problems are highly prevalent ⁶6. Garcia JBS, Hernandez-Castro JJ, Nunez RG, Pazos MA, Aguirre JO, Jreige A, et al. Prevalence of low back pain in Latin America: a systematic literature review. Pain Physician 2014; 17:379-91., one of the main reasons for medical visits, and account for serious losses in quality of life due to heavy suffering and societal and personal costs. As shown by the Global Burden of Disease study in 2010, held in 47 countries, chronic back problems are the leading cause of years of life lost to disability ⁷7. Hoy D, March L, Brooks P, Blyth F, Woolf A, Bain C, et al. The global burden of low back pain: estimates from the Global Burden of Disease 2010 study. Ann Rheum Dis 2014; 73:968-74..

Global prevalence of chronic back problems in the adult population in 2000 ranged from 12% to 33% ⁸8. Meucci RD, Fassa AG, Faria NMX. Prevalence of chronic low back pain: systematic review. Rev Saúde Pública 2015; 49:73.. Variations in prevalence in systematic reviews ²2. Dionne CE, Dunn KM, Croft PR. Does back pain prevalence really decrease with increasing age? A systematic review. Age Ageing 2006; 35:229-34.^,44. Dagenais S, Caro J, Haldeman S. A systematic review of low back pain cost of illness studies in the United States and internationally. Spine J 2008; 8:8-20.^,99. Gouveia M, Augusto M. Custos indirectos da dor crónica em Portugal. Revista Portuguesa de Saúde Pública 2011; 29:100-7.^,1010. Hoy D, Bain C, Williams G, March L, Brooks P, Blyth F, et al. A systematic review of the global prevalence of low back pain. Arthritis Rheum 2012; 64:2028-37.^,1111. Louw QA, Morris LD, Grimmer-Somers K. The prevalence of low back pain in Africa: a systematic review. BMC Musculoskeletal Disord 2007; 8:105. are due largely to difficulties in the precise anatomical-pathological diagnosis of the condition, variability in anatomical site (lumbar, back, or other), relevance of symptoms (such as pain) for definition of chronicity, and differences in the reference period for back problems in survey questions (days, months, or the previous year). Chronicity of back problems is generally defined as continuous pain for at least three months, regardless of possible limitations caused by the problem ⁸8. Meucci RD, Fassa AG, Faria NMX. Prevalence of chronic low back pain: systematic review. Rev Saúde Pública 2015; 49:73..

In Brazil, chronic back problems are also one of the most frequent chronic conditions in the population, with prevalence in adults 18 years or older of 18.5% (95%CI: 17.8-19.1), according to data from the Brazilian National Health Survey (PNS) in 2013 ¹²12. Oliveira MM, Andrade SSCDA, Souza CAV, Ponte JN, Szwarcwald CL, Malta DC. Problema crônico de coluna e diagnóstico de distúrbios osteomusculares relacionados ao trabalho (DORT) autorreferidos no Brasil: Pesquisa Nacional de Saúde, 2013. Epidemiol Serv Saúde 2015; 24:287-96.. Chronic back problems in the PNS are self-reported (not requiring a medical diagnosis), specifying the location (neck, lumbar area, vertebrae/discs) and including pain in the definition of chronicity.

Knowledge of the patient’s life cycle in relation to the condition, age bracket, and the problem’s impact on quality of life provides fundamental input for health promotion and the prevention of back problems in the population ⁹9. Gouveia M, Augusto M. Custos indirectos da dor crónica em Portugal. Revista Portuguesa de Saúde Pública 2011; 29:100-7.. However, there is little evidence of an association between prevalence of chronic back problems and age in Brazil, as underscored by Dionne et al. ²2. Dionne CE, Dunn KM, Croft PR. Does back pain prevalence really decrease with increasing age? A systematic review. Age Ageing 2006; 35:229-34. based on a systematic review of 51 articles, none of which were from Latin America. A systematic review from this perspective showed that although prevalence increases with age, the relationship is non-linear and stabilizes around 60 years ¹³13. Manek NJ, MacGregor J. Epidemiology of back disorders: prevalence, risk factors, and prognosis. Curr Opin Intern Med 2005; 4:324-30.. The relevance of chronic back problems in old age is due not to the increasing prevalence, but to the severity of limitations caused by them ²2. Dionne CE, Dunn KM, Croft PR. Does back pain prevalence really decrease with increasing age? A systematic review. Age Ageing 2006; 35:229-34.. Since the proportion of elderly individuals will increase considerably in the coming years in most countries, chronic back problems should be a priority in clinical and epidemiological research.

Due to the impacts on public health, Dionne et al. ²2. Dionne CE, Dunn KM, Croft PR. Does back pain prevalence really decrease with increasing age? A systematic review. Age Ageing 2006; 35:229-34. recommend that all countries ask about the severity of chronic back problems, pain, and limitations resulting from them. Brazil still lacks studies from this perspective, due mainly to the lack of population data on the limitations and restrictions caused by chronic back problems. According to a systematic review, studies on back problems generally lack a significant sample size and precise data collection instruments ¹⁴14. Nascimento PRC, Costa LOP. Prevalência da dor lombar no Brasil: uma revisão sistemática. Cad Saúde Pública 2015; 31:1141-56.. The PNS in 2013 was the first nationally representative large-scale study to address this question.

The unequal prevalence of chronic back problems according to lifestyle, general health status, and socioeconomic and demographic characteristics has been identified by various studies, especially in developed countries like England, Canada, Sweden, United States, and Denmark ¹1. Andersson GB. Epidemiological features of chronic low-back pain. Lancet 1999; 354:581-5.^,1515. Barros MBDA, Francisco PMSB, Zanchetta LM, César CLG. Tendências das desigualdades sociais e demográficas na prevalência de doenças crônicas no Brasil, PNAD: 2003-2008. Ciênc Saúde Coletiva 2011; 16:3755-68., but there is no consensus on the relevance and direction of each of the risk factors ¹³13. Manek NJ, MacGregor J. Epidemiology of back disorders: prevalence, risk factors, and prognosis. Curr Opin Intern Med 2005; 4:324-30.. Low schooling has been identified as one of the most robust predictors of high prevalence of chronic back problems ³3. Hoy D, Brooks P, Blyth F, Buchbinder R. The epidemiology of low back pain. Best Pract Res Clin Rheumatol 2010; 24:769-81.. Other individual factors identified in studies are sex, age, occupation, and obesity ⁶6. Garcia JBS, Hernandez-Castro JJ, Nunez RG, Pazos MA, Aguirre JO, Jreige A, et al. Prevalence of low back pain in Latin America: a systematic literature review. Pain Physician 2014; 17:379-91.^,1616. Govindu NK, Babski-Reeves K. Effects of personal, psychosocial and occupational factors on low back pain severity in workers. Int J Ind Ergon 2014; 44:335-41.^,1717. Kopec J, Sayre EC, Esdaile JM. Predictors of back pain in a general population cohort. Spine 2004; 29:70-8.^,1818. Webb R, Brammah T, Lunt M, Urwin M, Allison T, Symmons D. Prevalence and predictors of intense, chronic, and disabling neck and back pain in the UK general population. Spine 2003; 28:1195-202.. Depression ¹⁹19. Hurwitz EL, Morgenstern H, Yu F. Cross-sectional and longitudinal associations of low-back pain and related disability with psychological distress among patients enrolled in the UCLA Low-Back Pain Study. J Clin Epidemiol 2003; 56:463-71. and low self-rated health ²⁰20. Ferreira GD, Silva MC, Rombaldi AJ, Wrege ED, Siqueira F V, Hallal PC. Prevalência de dor nas costas e fatores associados em adultos do sul do Brasil: estudo de base populacional. Braz J Phys Ther 2011; 15:31-6. have also been related to chronic back problems.

The aim of this study is to analyze epidemiological aspects of chronic back problems in Brazil, such as prevalence and the association with demographic and socioeconomic factors, lifestyle, and health conditions, in addition to time lived with chronic back problems, the impact of limitations in daily living, and mean age at onset of symptoms according to sex, age bracket, and life cycle phase.

Methodology

Information source

The study uses micro-data from the PNS of 2013, conducted by the Brazilian Institute of Geography and Statistics (IBGE). The PNS is a household survey with a complex sampling design, representative of the population of Brazil and its major geographic regions, states, metropolitan areas, and state capitals ²¹21. Souza-Júnior PRB, Freitas MPS, Antonaci GDA, Szwarcwald CL. Desenho da amostra da Pesquisa Nacional de Saúde 2013. Epidemiol Serv Saúde 2015; 24:207-16.. The survey’s main objective is to characterize the population’s health status and lifestyle, in addition to collecting information on healthcare, access, and health services. The questionnaire consists of three parts, with the first two covering questions on household characteristics and the residents’ socioeconomic and health status; the third part is individual and is addressed to a previously selected household resident 18 years or older, with questions on health/disease and lifestyle ²²22. Szwarcwald CL, Malta DC, Pereira CA, Vieira MLFP, Conde WL, Souza Junior PRB, et al. Pesquisa Nacional de Saúde no Brasil: concepção e metodologia de aplicação. Ciênc Saúde Coletiva 2014; 19:333-42..

Brazil’s 2013 PNS covered a total sample of 60,202 individuals 18 years and older. The sampling plan was three-stage cluster (census tracts, households, and individuals). In the first stage, selection of the primary analytical unit used simple random sampling, selected previously in the master sample. In the second stage, simple random sampling was used to select a fixed number of permanent private households in each primary analytical unit selected in the first stage. In the third stage, in each household in the sample, a resident 18 years or older was selected (also by simple random sampling) to answer the third (individual) part of the questionnaire. This selection was based on a list of eligible residents prepared at the time of the interview ²¹21. Souza-Júnior PRB, Freitas MPS, Antonaci GDA, Szwarcwald CL. Desenho da amostra da Pesquisa Nacional de Saúde 2013. Epidemiol Serv Saúde 2015; 24:207-16..

Variables

Prevalence of chronic back problems was measured with the question: “Do you have some chronic back problem, like chronic pain in your back or neck, lumbago, sciatica, or problems in the vertebrae or discs?” The answer was dichotomous (yes or no).

Severity of chronic back problems was examined by prevalence according to the degree of limitation in activities of daily living, measured with the question: “In general, to what degree does your back problem limit your daily activities (working, housework, etc.)?” the categories were: (1) does not limit; (2) a little; (3) moderately; (4) intensely; and (5) very intensely. In the current study, the outcome was reclassified in four categories according to degree of limitation: absent, mild, moderate, and intense, with the latter combining “intensely” and “very intensely”.

Mean age at onset of chronic back problems was calculated with the question: “How old were you when your back problem began?” The age variable was used both in five-year brackets (for studying the limitations caused by chronic back problems) and in three categories (18-49, 50-59, and ≥ 60 years) for analysis of the patient’s life cycle in relation to chronic back problems (to calculate the prevalence and prevalence ratio).

The association between chronic back problems and demographic, socioeconomic, behavioral, and health characteristics was analyzed according to the following variables: sex (male; female), age bracket (18-49, 50-59, and ≥ 60 years), area of residence (urban versus rural), race/color (white, brown, black, indigenous, Asian-descendant), schooling (university or greater, complete secondary, complete primary, incomplete primary, none), self-rated health (very good, good, fair, bad, or very bad), the most prevalent chronic diseases in the population (arterial hypertension or high blood pressure, depression, arthritis or rheumatism, asthma or asthmatic bronchitis, and heart diseases including infarction, angina, congestive heart failure, or other), body mass index - BMI (underweight: < 18.5kg/m²; normal weight: 18.5-24.9kg/m²; overweight: 25.0-29.9kg/m²; and obesity: > 30kg/m²).

Statistical analysis

The study of severity and characteristics of chronic back problems in Brazil was based on analysis of prevalence according to sex and age.

Strength of association between chronic back problems and risk factors was analyzed using prevalence ratios (PR) and 95% confidence intervals (95%CI), calculated by Poisson regression, where the dependent variable was presence of chronic back problems and the independent variables were: sex, schooling, area of residence, race/color, self-rated health, type of chronic disease, body mass index (BMI), and physical activity. Crude (bivariate) and adjusted prevalence ratios were calculated according to all the independent variables. The models were also stratified by age bracket to identify differences in the strength of association between risk factors and chronic back problems in different age groups.

Due to the complex, multi-stage sampling design, all the analyses were done with the Stata 14.0 survey library (StataCorp LP, College Station, USA).

Results

The results represent the Brazilian population 18 years and older in the PNS, the majority of whom were females (52.9%) and 18 to 49 years of age (64.8%). Some 40% had low schooling (up to incomplete primary schooling or the equivalent), 47.5% were white and 42% brown, and only 13.8% lived in rural areas. As for health, fewer than 50% had adequate weight, approximately 69% rated their health as good or very good, 21% had been diagnosed with hypertension, and less than 10% had any other of the chronic diseases included in the analysis.

Estimated time with back pain (Table 1) confirms its chronic nature: 95% of the sample reported that symptoms had begun at least a year before. In fact, 73.4% reported symptom for more than 5 years.

The prevalence of chronic back problems was 18.5% (95%CI: 17.8-19.1), and was higher in women than in men (21.1%, 95%CI: 20.2-21.9) and increased with age, reaching 28.1% (95%CI: 26.6-29.7) at 60 years.

Table 1 lists socioeconomic differences and risk factors for prevalence of chronic back problems. Adults with less schooling (none or incomplete primary) had higher prevalence of chronic back problems than those with more schooling. The urban population showed slightly higher prevalence when compared to rural residents (21.3%, 95%CI: 19.6-23.1). Prevalence of chronic back problems by race/color did not show a major difference, but was slightly higher in whites (19%, 95%CI: 18.4-20.2). Prevalence was higher in individuals with worse self-rated health: 43.9% among those with bad or very bad self-rated health (95%CI: 41.1-46.8) and only 8.4% in those who rated their health as very good. Obese individuals showed higher prevalence of chronic back problems (22.3%, 95%CI: 20.7-24) than normal weight (16.7%, 95%CI: 15.7-17.8) or underweight individuals (17.4%, 95%CI: 13.0-22.8). Individuals with chronic comorbidities generally showed higher prevalence of chronic back problems: one out of two individuals with arthritis also had chronic back problems (50.4% 95%CI: 47.8-53); among those with depression, prevalence of chronic back problems was 39.3% (95%CI: 36.9-41.8); and among those with chronic heart disease it was 37.3%, (95%CI: 33.8-41.0).

Figure 1 represents the patient’s life cycle in relation to chronic back problems, according to sex. Prevalence of chronic back problems and that of chronic back problems with some limitation showed similar trends: it increased progressively up to 50 years of age, when it stabilized. From that age on, the increases were no longer significant when compared to the more elderly groups. In the transition from the younger age bracket (18 to 19 years) to adulthood (30 to 34), prevalence of chronic back problems doubled (from 6.06% to 12.45%) and quadrupled in the 50 to 54 year bracket (25.7%).

Prevalence of chronic back problems and chronic back problems with some limitation was higher in women than in men. There was also an increase (although not significant) starting at 50 years. Mean age at onset of chronic back problems was 35 years, similar between the sexes and increasing with age (Table 2).

Chronic back problems caused some limitation (mild, moderate, or intense) in activities of daily living (ADL) in 67% of those with the condition (Table 2): mild in 32.6%, moderate in 18.3%, and intense in 16.4%. Starting at 50 years of age, 70% of individuals with chronic back problems presented some limitation and some 20% suffered intense limitations in ADL, regardless of gender. The proportion of individuals with mild limitation remained stable in the age brackets (some 30%), but limitations in ADL increased gradually with age (intense limitation increased from 2.8% at 18 years to 20.2% at 75), stabilizing around 50 years. Limitations in ADL had a similar impact in men and women.

Figure 2 shows the changes in intensity of limitation according to age bracket. The proportion of persons with mild limitation decreased gradually up to 40 years, while the proportion of moderate and intense limitations increased with age (32% at 25 years and 60% at 55 years). Women in younger age brackets suffered more intense limitations.

PR showed that women had a higher likelihood than men of presenting chronic back problems (PR = 1.18, 95%CI: 1.11-1.25), with larger disadvantages in youth and adulthood, from 18 to 49 years (PR = 1.26, 95%CI: 1.15-1.38) (Table 3). Female gender only failed to show a significant difference in the 50 to 59 year age bracket.

Less schooling was significantly associated with chronic back problems: persons with no schooling or that had not finished primary school shower a higher likelihood of chronic back problems in all age brackets when compared to those with a university education or more. Complete primary or incomplete secondary school only showed a significant association in the 50 to 59 year bracket.

As for area of residence, persons living in rural areas showed a PR of chronic back problems 10% greater than those living in urban areas (PR = 1.10, 95%CI: 1.01-1.20).

Brown (mixed-race) individuals showed lower prevalence of back problems when compared to whites in the overall general population (PR = 0.91, 95%CI: 0.85-0.97) and in the 50 to 59 year age bracket (PR = 0.86, 95%CI: 0.76-0.97). Persons self-classified as black, indigenous, or Asian-descendant showed a lower probability of chronic back problems when compared to whites in the overall population (PR = 0.90, 95%CI: 0.81-0.99), but not according to age bracket.

Self-rated health was heavily associated with chronic back problems. Persons with bad or very bad self-rated health had three times greater likelihood of chronic back problems (PR = 3.32, 95%CI: 2.84-3.87) when compared to those with very good self-rated health. With fair self-rated health, the prevalence ratio for chronic back problems was 2.5 (PR = 2.59, 95%CI: 2.23-3.00). The effect of self-rated health on chronic back problems was relevant in nearly all the categories, but the effect’s weight decreased with age.

Various chronic diseases were associated with chronic back problems. The diseases showing the strongest association with chronic back problems were arthritis (PR = 1.76, 95%CI: 1.64-1.89) and depression (PR = 1.51, 95%CI: 1.41-1.63), similar in all age brackets. Chronic heart disease increased by 15% the likelihood of chronic back problems in the general population (PR = 1.15, 95%CI: 1.03-1.28), and this association was stronger in the 18 to 49 year bracket (PR = 1.31, 95%CI: 1.06-1.63).

Hypertension increased the likelihood of chronic back problems by 9% in the general population (PR = 1.09, 95%CI: 1.02-1.17) and by 24% in the 18 to 49 year age bracket (PR = 1.24, 95%CI: 1.11-1.38). Asthma also increased the risk of chronic back problems by 23% in the general population (PR = 1.26, 95%CI: 1.14-1.40). Diabetes was associated statistically with fewer chronic back problems in the general population and in young people, but the association lost significance starting at the 50 to 59 year age bracket. In the general population, the prevalence ratio for chronic back problems was 17% lower among individuals with diabetes (PR = 0.83, 95%CI: 0.75-0.91).

BMI was not associated significantly with chronic back problems in the general population. As for age bracket, among individuals 18 to 49 years of age, overweight was a risk factor compared to normal weight (PR = 1.19, 95%CI: 1_.06-1.33), while in the 50 to 59 year bracket, obesity was associated with fewer chronic back problems (PR = 0.82, 95%CI: 0.69-0.98). Physical activity was not associated significantly with chronic back problems in any of the age brackets.

Discussion

The prevalence of chronic back problems (18.5%) indicates that some 25 million Brazilians 18 years and older suffer from this condition. This result is consistent with a meta-analysis by Hoy et al. ¹⁰10. Hoy D, Bain C, Williams G, March L, Brooks P, Blyth F, et al. A systematic review of the global prevalence of low back pain. Arthritis Rheum 2012; 64:2028-37., covering 165 studies from 54 countries: median prevalence of chronic back problems was 19.4%, and mean prevalence was 18.1%. Importantly, it is a challenge to compare the prevalence of chronic back problems, due mainly to the methodological heterogeneity between studies and the difficulties in obtaining valid population estimates.

Mean age at onset of chronic back problems was 35 years in our study, similar between the sexes and increasing with age. The result was similar to that of an Australian study ²³23. Walker BF, Muller R, Grant WD. Low back pain in australian adults. Prevalence and associated disability. J Manipulative Physiol Ther 2004; 27:238-44. in which mean age at the first complaint of back pain was 28.4 years.

The PNS does not provide information on chronic back problems in children and adolescents, due to the sample design. However, the question concerning age at onset of chronic back problems showed that among younger adults (18 to 25 years), mean age at onset of chronic back problems was between 14 and 16 years. This finding corroborates studies conducted in other countries, showing that prevalence increases greatly in early adolescence, especially in girls ¹⁰10. Hoy D, Bain C, Williams G, March L, Brooks P, Blyth F, et al. A systematic review of the global prevalence of low back pain. Arthritis Rheum 2012; 64:2028-37.^,2424. De Vitta A, Martinez MG, Piza NT, Simeão SFAP, Ferreira NP. Prevalência e fatores associados à dor lombar em escolares. Cad Saúde Pública 2011; 27:1520-8.. We thus conclude that the study of causes and the prevention of chronic back problems should begin in childhood ²⁵25. Leboeuf-Y de C, Kyvik KO. At what age does low back pain become a common problem? A study of 29,424 individuals aged 12-41 years. Spine 1998; 23:228-34..

The chronicity of back problems studied in the PNS was confirmed by calculation of the time since onset of the condition. In this study, 95.5% of individuals with back problems reported back pain for at least a year. However, future studies should specify in the question the minimum duration for defining back pain as chronic, considering the lack of consensus on this issue ²2. Dionne CE, Dunn KM, Croft PR. Does back pain prevalence really decrease with increasing age? A systematic review. Age Ageing 2006; 35:229-34..

The analysis of patient’s life cycle in chronic back problems, from 18 years to old age, showed a similar trend to other studies ²2. Dionne CE, Dunn KM, Croft PR. Does back pain prevalence really decrease with increasing age? A systematic review. Age Ageing 2006; 35:229-34.^,2626. Deyo RA, Weinstein JN. Low back pain. N Engl J Med 2001; 344:363-70.: prevalence of chronic back problems increases quickly until young adulthood (around 6% at 18 years and 12% at 30 years) and stabilizes after 50 years of age. Dionne et al. ²2. Dionne CE, Dunn KM, Croft PR. Does back pain prevalence really decrease with increasing age? A systematic review. Age Ageing 2006; 35:229-34., in a systematic review of hypotheses for the leveling of prevalence of chronic back problems with advancing age, highlight that cognitive impairment, greater tolerance of pain, and increasing comorbidities could explain this stability in old age.

The severity of chronic back problems also increases with age. In Brazil, starting at 50 years, 70% of individuals with chronic back problems suffered some limitation. Intense and very intense limitations in ADL increased in prevalence from 2.8% at 18 years to 20.2% at 75. This result agrees with the Global Burden of Disease study ⁷7. Hoy D, March L, Brooks P, Blyth F, Woolf A, Bain C, et al. The global burden of low back pain: estimates from the Global Burden of Disease 2010 study. Ann Rheum Dis 2014; 73:968-74. showing chronic back problems as one of the main problems leading to losses in quality-adjusted life years. The degree of intensity of limitations in ADL did not differ between men and women. International studies suggest that intensity of pain is associated with degree of limitation ²⁷27. Manchikanti L, Singh V, Datta S, Cohen SP, Hirsch J. Comprehensive review of epidemiology, scope, and impact of spinal pain. Pain Physician 2009; 12:35-70., especially among the elderly ²⁸28. Weiner DK, Haggerty CL, Kritchevsky SB, Harris T, Simonsick EM, Nevitt M, et al. How does low back pain impact physical function in independent, well - functioning older adults? Evidence from the health ABC Cohort and implications for the future. Pain Med 2003; 4:311-20..

Compared to men, women showed higher prevalence of chronic back problems and more limitations in ADL caused by chronic back problems. Starting at 65 years, the severity of limitations in ADL was more intense in women. Various international studies point to this gender inequality ²⁶26. Deyo RA, Weinstein JN. Low back pain. N Engl J Med 2001; 344:363-70.^,2929. Andersson GBJ. Epidemiology of low back pain. Acta Orthop Scand Suppl 1998; 281:28-31.^,3030. Kwon M, Shim WS, Kim MH, Gwak MS, Hahm TS, Kim GS, et al. A correlation between low back pain and associated factors: a study involving 772 patients who had undergone general physical examination. J Korean Med Sci 2006; 21:1086-91.^,3131. Wong EY, Deyo RA. Acute low back pain. Primary Care Update for OB/GYNS 2001; 8:171-4., and two hypotheses are musculoskeletal makeup and daily activities performed by women ⁶6. Garcia JBS, Hernandez-Castro JJ, Nunez RG, Pazos MA, Aguirre JO, Jreige A, et al. Prevalence of low back pain in Latin America: a systematic literature review. Pain Physician 2014; 17:379-91.. Hoy et al. ⁷7. Hoy D, March L, Brooks P, Blyth F, Woolf A, Bain C, et al. The global burden of low back pain: estimates from the Global Burden of Disease 2010 study. Ann Rheum Dis 2014; 73:968-74. highlight other hypotheses for the higher prevalence in women, like osteoporosis, menstruation, pregnancy, and cultural factors.

The current study confirms the association between presence of chronic back problems and demographic, socioeconomic, behavioral, and health conditions, with bad self-rated health, presence of comorbidities (arthritis, depression, and asthma), and low schooling as the leading risk factors, as identified in various international studies ¹1. Andersson GB. Epidemiological features of chronic low-back pain. Lancet 1999; 354:581-5.^,33. Hoy D, Brooks P, Blyth F, Buchbinder R. The epidemiology of low back pain. Best Pract Res Clin Rheumatol 2010; 24:769-81.^,1515. Barros MBDA, Francisco PMSB, Zanchetta LM, César CLG. Tendências das desigualdades sociais e demográficas na prevalência de doenças crônicas no Brasil, PNAD: 2003-2008. Ciênc Saúde Coletiva 2011; 16:3755-68.^,3030. Kwon M, Shim WS, Kim MH, Gwak MS, Hahm TS, Kim GS, et al. A correlation between low back pain and associated factors: a study involving 772 patients who had undergone general physical examination. J Korean Med Sci 2006; 21:1086-91..

Schooling has been associated with prevalence of chronic back problems ³3. Hoy D, Brooks P, Blyth F, Buchbinder R. The epidemiology of low back pain. Best Pract Res Clin Rheumatol 2010; 24:769-81.^,3030. Kwon M, Shim WS, Kim MH, Gwak MS, Hahm TS, Kim GS, et al. A correlation between low back pain and associated factors: a study involving 772 patients who had undergone general physical examination. J Korean Med Sci 2006; 21:1086-91.. In Brazil, prevalence of chronic back problems was 26% higher in individuals with no schooling compared to those with a university education. Plouvier et al. ³²32. Plouvier S, Leclerc A, Chastang JF, Bonenfant S, Goldberg MS, Plouvier S, et al. Socioeconomic position and low-back pain - the role of biomechanical strains and psychosocial work factors in the GAZEL cohort. Scandinavian Journal of Work, Environment & Health 2009; 35:429-36. suggest that differences in work characteristics explain a substantial part of this association, since individuals with low schooling are more exposed to poor working conditions.

As for race/color, whites showed a higher prevalence of chronic back problems than the other categories, but the association was weak and lost significance when analyzed by age bracket. The results of a study in Bahia State, Brazil, differed from ours ³³33. Almeida ICGB, Sá KN, Silva M, Baptista A, Matos MA, Lessa I. Prevalência de dor lombar crônica na população da Cidade de Salvador. Rev Bras Ortop 2008; 43:96-102.. As reported by Manchikanti ²⁷27. Manchikanti L, Singh V, Datta S, Cohen SP, Hirsch J. Comprehensive review of epidemiology, scope, and impact of spinal pain. Pain Physician 2009; 12:35-70., there are still few studies analyzing the relationship between race/color and chronic back problems.

Self-rated health is considered a good indicator of quality of life and morbidity, and an important predictor of subsequent mortality, which has drawn considerable interest in studies in the last three decades ³⁴34. Manderbacka K, Kåreholt I, Martikainen P, Lundberg O. The effect of point of reference on the association between self-rated health and mortality. Soc Sci Med 2003; 56:1447-52.. A strong association was found between bad or very bad self-rated health and chronic back problems, confirming findings from studies both in the adult population in the South of Brazil ²⁰20. Ferreira GD, Silva MC, Rombaldi AJ, Wrege ED, Siqueira F V, Hallal PC. Prevalência de dor nas costas e fatores associados em adultos do sul do Brasil: estudo de base populacional. Braz J Phys Ther 2011; 15:31-6. and in international studies ¹⁷17. Kopec J, Sayre EC, Esdaile JM. Predictors of back pain in a general population cohort. Spine 2004; 29:70-8.^,3535. Dionne CE, Koepsell TD, Von Korff M, Deyo RA, Barlow WE, Checkoway H. Predicting long-term functional limitations among back pain patients in primary care settings. J Clin Epidemiol 1997; 50:31-43.. Interestingly, with advancing age, the association between bad self-rated health and chronic back problems loses strength.

Arthritis, depression, and asthma were the diseases most frequently associated with chronic back problems, confirming international findings ³⁶36. Stewart Williams J, Ng N, Peltzer K, Yawson A, Biritwum R, Maximova T, et al. Risk factors and disability associated with low back pain in older adults in low- and middle-income countries. Results from the WHO Study on Global Ageing and Adult Health (SAGE). PLoS One 2015; 10:e0127880.. Although depression and chronic back problems are closely related, the order of causality is not clear; Hurwitz et al. ¹⁹19. Hurwitz EL, Morgenstern H, Yu F. Cross-sectional and longitudinal associations of low-back pain and related disability with psychological distress among patients enrolled in the UCLA Low-Back Pain Study. J Clin Epidemiol 2003; 56:463-71. suggest that the conditions are interdependent.

The association between area of residence (urban/rural) and chronic back problems was weak, similar to the findings by Hoy ¹⁰10. Hoy D, Bain C, Williams G, March L, Brooks P, Blyth F, et al. A systematic review of the global prevalence of low back pain. Arthritis Rheum 2012; 64:2028-37.. BMI and physical activity were not relevant to the risk of chronic back problems. Although various international studies point to obesity as a predictor of chronic back problems ⁶6. Garcia JBS, Hernandez-Castro JJ, Nunez RG, Pazos MA, Aguirre JO, Jreige A, et al. Prevalence of low back pain in Latin America: a systematic literature review. Pain Physician 2014; 17:379-91.^,1010. Hoy D, Bain C, Williams G, March L, Brooks P, Blyth F, et al. A systematic review of the global prevalence of low back pain. Arthritis Rheum 2012; 64:2028-37.^,1818. Webb R, Brammah T, Lunt M, Urwin M, Allison T, Symmons D. Prevalence and predictors of intense, chronic, and disabling neck and back pain in the UK general population. Spine 2003; 28:1195-202.^,3737. Silva MC, Fassa AG, Valle NC. Dor lombar crônica em uma população adulta do Sul do Brasil: prevalência e fatores associados. Cad Saúde Pública 2004; 20:377-85., our study did not find an association with high BMI. Leboeuf-Yde ³⁸38. Leboeuf-Yde C. Body weight and low back pain. A systematic literature review of 56 journal articles reporting on 65 epidemiologic studies. Spine (Phila Pa 1976) 2000; 25:226-37., in a review article, found conflicting results in the literature.

One of the study’s limitations was the definition of chronic back problems used in the PNS. The question in the survey included neck, lumbar, vertebrae, discs, and even sciatic pain, and did not set a minimum time to define it as a chronic problem. The generic definition of the outcome hinders comparison with international studies. Cedraschi et al. ³⁹39. Cedraschi C, Robert J, Goerg D, Perrin E, Fischer W, Vischer TL. Is chronic non-specific low back pain chronic? Definitions of a problem and problems of a definition. Br J Gen Pract 1999; 49:358-62. found a discrepancy between theory and practice on the definition of chronic back problems. The authors discuss the ambiguity in the definition of chronicity of back problems and low back pain (both for patients and health professionals), partly due to the event’s timeline, but also because not only objective physical conditions lead to chronic back problems, but the self-reported pain and limitations should be considered in the definition ³⁹39. Cedraschi C, Robert J, Goerg D, Perrin E, Fischer W, Vischer TL. Is chronic non-specific low back pain chronic? Definitions of a problem and problems of a definition. Br J Gen Pract 1999; 49:358-62.. In most international studies, back problems refer to the lumbar area and include pain.

We suggest that future surveys on this problem include better wording of the question and standardized orientation for the answers. Another limitation was the cross-sectional design, in which it is not possible to determine if the exposure occurred before the outcome, and there may be problems of reverse causality. In the current study, such variables as self-rated health, depression, and BMI, among others, may have undergone changes after the onset of chronic back problems, influencing the strength of association.

The high prevalence and impact on living conditions reveal the need for epidemiological studies on chronic back problems. The results suggest that health promotion and prevention of chronic back problems should be intensified, especially before 50 years of age, considering Brazil’s aging population.

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