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Abstract

  1. Top of page
  2. Abstract
  3. What's already known about this topic?
  4. What does this study add?
  5. Introduction
  6. Materials and methods
  7. Results
  8. Discussion
  9. Author contributions
  10. Acknowledgements
  11. References

Background

Low back pain (LBP) is a prevalent problem and tends to be socio-economically patterned. Relatively little is known about life-course socio-economic circumstances as determinants of different types of LBP. Our aim was to examine whether childhood and adult socio-economic position and social mobility are associated with radiating and non-specific LBP and sciatica.

Method

Data were derived from the Young Finns Study (n = 2231). Childhood socio-economic position was based on parental education, occupational class and family income at baseline in 1980. Data on own education and LBP outcomes were collected at the end of follow-up in 2007. Social mobility was based on parental and own education. Covariates were composed of age, parental body mass index and smoking.

Results

Both childhood and own socio-economic position remained associated with radiating LBP and sciatica after adjustments. However, the associations varied by socio-economic indicator and gender. Stable lower socio-economic position and downward mobility were associated with radiating LBP.

Conclusion

Childhood socio-economic circumstances affect the risk of radiating LBP and sciatica in adulthood. To prevent low back disorders, early socio-economic circumstances need to be considered alongside own socio-economic position.


What's already known about this topic?

  1. Top of page
  2. Abstract
  3. What's already known about this topic?
  4. What does this study add?
  5. Introduction
  6. Materials and methods
  7. Results
  8. Discussion
  9. Author contributions
  10. Acknowledgements
  11. References
  • Low back pain is a prevalent public health problem and it is socially patterned.
  • Life-course social determinants of different types of low back pain are poorly understood.

What does this study add?

  1. Top of page
  2. Abstract
  3. What's already known about this topic?
  4. What does this study add?
  5. Introduction
  6. Materials and methods
  7. Results
  8. Discussion
  9. Author contributions
  10. Acknowledgements
  11. References
  • Childhood socio-economic circumstances are associated with low back disorders in adulthood independent of own socio-economic position.
  • Stable lower and decreasing socio-economic position increase particularly the risk of radiating low back pain.
  • Socio-economic differences in non-specific low back pain are practically non-existent.

Introduction

  1. Top of page
  2. Abstract
  3. What's already known about this topic?
  4. What does this study add?
  5. Introduction
  6. Materials and methods
  7. Results
  8. Discussion
  9. Author contributions
  10. Acknowledgements
  11. References

Low back pain (LBP) is a prevalent condition with high recurrence and persistence across different populations (Hoy et al., 2010). Chronic pain is recognized as a notable public health problem worldwide (Croft et al., 2010). In Finland, around half of adult population has reported LBP in repeated cross-sectional surveys (Heistaro et al., 1998).

LBP is socio-economically patterned with low own education and manual work being the most consistent socio-economic determinants of LBP or back pain in general (Heistaro et al., 1998; Hagen et al., 2000; Latza et al., 2000; Dionne et al., 2001; Saastamoinen et al., 2005; Kääriä et al., 2006; Plouvier et al., 2009). However, relatively little is known about the socio-economic circumstances across life course as determinants of LBP in adulthood. A Canadian study showed that low childhood socio-economic position is associated with incident back pain in early adulthood (Mustard et al., 2005). An earlier Finnish study found strong associations between parental occupational class and LBP among adolescents (Sjolie, 2004). Reports on LBP were persistent over follow-up, highlighting the importance of prevention and focus on early risk factors. Additionally, previous studies among British young adults have shown that childhood and adult social class are associated with chronic widespread pain (Power et al., 2007) and parental occupational class with back pain (Power and Matthews, 1997). In contrast, a study among Danish adolescents found no or only weak associations between childhood and own socio-economic circumstances and LBP (Hestbaek et al., 2008).

Previous evidence is mostly derived from cross-sectional and heterogeneous study populations. Pain measures have varied or social determinants of LBP have not been the main focus. Different types of LBP might have unique risk factors and different aetiology (Heliövaara et al., 1991). Thus, it needs to be examined whether socio-economic determinants differ for low back disorders and non-specific LBP, and whether childhood socio-economic circumstances affect LBP independent of own socio-economic position. More evidence is also needed for women and men, as the risk factors may be sex specific (Heliövaara et al., 1991; Shiri et al., 2008).

Finally, the importance of life-course perspectives has been recently highlighted (Bond, 2012; Marmot et al., 2012), and the need to extend life-course epidemiology to the study of back pain has been emphasized (Dunn, 2010; Macfarlane, 2010). There is a need to fill in the evidence gap by examining which socio-economic determinants in different stages of life affect specific types of LBP. Focus on such multiple socio-economic circumstances is important as socio-economic position is a broad, multidimensional concept that covers a range of social and material circumstances across life course, each reflecting not only one's ranking in society but also unique circumstances with potentially disparate health effects (Lynch and Kaplan, 2000; Lahelma et al., 2004; Galobardes et al., 2007).

The aim of this study was to examine multiple indicators of childhood socio-economic position as determinants of different types of LBP outcomes among women and men. A further aim was to examine whether the associations remain after considering own socio-economic position and covariates. Finally, social mobility was examined.

Materials and methods

  1. Top of page
  2. Abstract
  3. What's already known about this topic?
  4. What does this study add?
  5. Introduction
  6. Materials and methods
  7. Results
  8. Discussion
  9. Author contributions
  10. Acknowledgements
  11. References

Data

Data for the study were derived from the ongoing Young Finns Study (Raitakari et al., 2008). Baseline data for the Young Finns Study were collected in 1980 among children and adolescents aged 3, 6, 9, 12, 15 and 18 years (n = 3596, response rate 83%). The participants were randomly selected from national registers. After the baseline, follow-up surveys have been conducted in 1983, 1986, 2001 and 2007. In this study, socio-economic data were derived from the baseline survey, and LBP outcomes from 2007 yielding a total follow-up time of 27 years (n = 2231, age range 30–45 years). The data have remained representative of the target population and some dropouts have returned to the survey later on (Raitakari et al., 2008).

Life-course socio-economic circumstances

Childhood socio-economic data at baseline included mother's and father's years of education (less than 9 years, 9–12 years and more than 12 years), social class (upper and lower non-manuals, manual workers and farmers) and family income level (low, intermediate, high). Own socio-economic position was assessed by educational level in 2007. It was classified into low (comprehensive school), intermediate (secondary education) and high education (academic level). In this cohort, own education was used, as it is the most robust indicator of own socio-economic position. It has been completed by most of the participants at follow-up providing better opportunities to examine its causal associations with low back disorders and sciatica, and moreover, it usually precedes the occupation and subsequent income level.

Social mobility was examined combining data on parental and own education. Stable high socio-economic position referred to the highest education of parents and academic own education. Stable lower education referred to stable low or intermediate education. Intermediate categories were composed of upward mobility (from low or intermediate to high) and downward mobility (from high to intermediate or low). Those with stable high education were used as a reference group. These participants were assumed to have had the lowest prevalence of physical exposures and other risk factors in childhood and adulthood. Years of education was used to measure parental and own education, as the Finnish educational system has dramatically changed over the previous decades, and therefore, education qualifications between parents and their children are not directly comparable. Due to the changes and as we had several age groups, using years of education was the best option in this study. This reflects the level of education and also the hierarchy in the society. Further details of measures of socio-economic position can be found elsewhere (Pulkki et al., 2003; Kivimäki et al., 2005).

Low back pain

Outcomes were composed of self-reported sciatica, radiating LBP and non-specific LBP. Sciatica referred to a clinically defined condition diagnosed by a physician. Participants were classified as having radiating LBP (pain that radiates below the knee) or non-specific LBP if they reported that their pain had lasted 7 days or more during the previous 12 months. Similar procedures have been applied also previously (Shiri et al., 2010b, 2013).

Covariates

Age was adjusted for as a covariate, as the study sampling was based on six age clusters. Further covariates included parental body mass index (BMI) and smoking. These covariates were included as they were assumed to be related to parents' socio-economic position and reflect their dietary and physical activity patterns, which were further assumed to affect those of the children and trait to adulthood risk factors. Participants' own smoking and BMI were omitted as these were assumed to be on the pathway between childhood socio-economic position and LBP, were measured at the same time with the outcome and would therefore produce mixed causal interpretation. Because mediating factors or mechanisms explaining the associations were out of the scope of this paper, we did not adjust for any further variables that might be on the path of the examined associations. Only mediating effects of own education were considered, alongside social mobility. Parental BMI was computed from self-reported heights and weights. If the data were missing, median value was imputed. Exposure to parental smoking referred to regular smoking of either parent that had lasted at least a year at baseline.

Statistical analyses

Sex-specific, age-adjusted prevalence of LBP outcomes was calculated by life-course socio-economic circumstances. Next, logistic regression analysis was used to examine socio-economic determinants of LBP [odds ratios (OR) and their 95% confidence intervals (95% CI)]. Age-adjusted bivariate models were fitted first (Model 1). Secondly, parental smoking and BMI were adjusted for (Model 2). Third, own education was adjusted for alongside mutual adjustment for all other covariates (Model 3). These factors were assumed to act as confounders of the association between childhood socio-economic position and LBP in adulthood. When the focus was on social mobility, Models 1 and 2 were similarly fitted. In addition, sensitivity analyses were conducted, examining those with only radiating or only non-specific pain. However, the results remained. Since we tested a set of a priori stated hypotheses, the adjustment for multiple comparisons was not performed (Thompson, 1998). All the analyses were conducted using an SAS Program version 9.2 (SAS Institute Inc., Cary, NC, USA).

Ethics

The study has received ethical approvals from the local ethics committees.

Results

  1. Top of page
  2. Abstract
  3. What's already known about this topic?
  4. What does this study add?
  5. Introduction
  6. Materials and methods
  7. Results
  8. Discussion
  9. Author contributions
  10. Acknowledgements
  11. References

Prevalence of LBP and sciatica

Prevalence of sciatica was 10% among women and 7% among men at follow-up, while that of radiating LBP was 20% among women and 18% among men (Table 1). Non-specific LBP was reported by 37% of women and 33% of men at follow-up. Altogether, 12% of all participants reported both non-specific LBP and radiating LBP, while 5% reported both non-specific pain and sciatica.

Table 1. Prevalence (%) of low back pain (LBP) outcomes and distribution of socio-economic variables among women (n = 1229) and men (n = 1002)
 Women (n = 1229)Men (n = 1002)
Sciatica10.06.6
Radiating LBP19.617.8
Non-specific LBP36.532.8
Parental occupational class in 1980  
Upper non-manual16.317.6
Lower non-manual43.939.7
Manuals (upper or lower)26.328.5
Farmers13.514.2
Parental education in 1980  
Less than 9 years39.035.4
9–12 years37.538.8
More than 12 years23.425.9
Family income level in 1980  
Low26.425.4
Intermediate51.852.6
High21.821.9
Own education in 2007  
Low (comprehensive school)3.86.3
Intermediate (secondary level, non-academic)69.671.4
High education (academic level)26.622.3
Social mobility (1980–2007)  
Stable high position11.111.4
Upward mobility15.810.9
Downward mobility12.414.4
Stable lower position (low/intermediate level)60.763.3

Among women, the prevalence of sciatica (p-value for trend <0.0001) and radiating LBP (p-value for trend 0.028) at follow-up increased with age, while corresponding patterns were not found for non-specific LBP (Table 2). Both sciatica and radiating LBP tended to be more prevalent among women with low childhood socio-economic position. For non-specific LBP, socio-economic differences were mostly non-existent.

Table 2. Age-adjusted prevalence of low back pain (LBP) outcomes by socio-economic circumstances across life course among women (n = 1146)
 SciaticaRadiating LBPNon-specific LBP
%95% CI%95% CI%95% CI
Age in 2007      
30 years6.11.5–10.715.89.7–21.843.836.4–51.2
33 years4.90.8–9.015.39.8–20.736.429.7–43.1
36 years9.14.8–13.418.613.0–24.332.825.9–39.7
39 years12.28.2–16.123.218.0–28.436.730.3–43.1
42 years11.57.4–15.620.515.0–26.037.530.8–44.2
45 years16.411.9–20.922.416.4–28.331.524.3–38.8
Parental occupational class in 1980      
Upper non-manual8.03.8–12.214.69.0–20.237.230.3–44.0
Lower non-manual9.97.3–12.619.916.4–23.337.933.7–42.1
Manuals (upper or lower)13.29.8–16.622.517.9–27.039.534.0–45.1
Farmers6.71.9–11.517.110.9–23.424.817.1–32.5
Parental education in 1980      
Less than 9 years11.28.3–14.119.816.0–23.734.429.7–39.1
9–12 years9.97.1–12.822.318.6–26.038.333.7–42.9
More than 12 years8.34.8–11.913.89.0–18.536.730.9–42.5
Family income level in 1980      
Low12.48.9–15.823.418.8–27.938.032.4–43.6
Intermediate10.27.8–12.519.516.3–22.735.831.9–39.7
High7.13.4–10.814.19.2–19.036.230.3–42.2
Own education in 2007      
Low (comprehensive school)11.82.6–21.021.39.2–33.331.316.0–46.7
Intermediate (secondary level, non-academic)10.88.7–12.922.619.9–25.438.435.0–41.8
High education (academic level)7.94.6–11.210.86.5–15.132.327.1–37.6
Social mobility (1980–2007)      
Stable high position8.53.4–13.68.82.1–15.537.529.3–45.7
Upward mobility7.53.2–11.812.26.5–17.828.721.8–35.6
Downward mobility8.23.3–13.118.211.7–24.735.727.6–43.7
Stable lower position (low/intermediate level)11.49.1–13.723.520.6–26.538.634.9–42.3

Among men, similar to women, sciatica was more prevalent with increasing age (p-value for trend 0.0015), while age trends were not statistically significant for radiating and non-specific LBP (Table 3). Further in line with women, LBP tended to be more prevalent among men with low childhood socio-economic position. Opposite to women, men raised in a farm reported more sciatica and radiating LBP than their higher class counterparts.

Table 3. Age-adjusted prevalence of low back pain (LBP) outcomes by socio-economic circumstances across life course among men (n = 944)
 SciaticaRadiating LBPNon-specific LBP
%95% CI%95% CI%95% CI
Age at follow-up in 2007      
30 years4.40.6–8.213.88.0–19.733.125.9–40.4
33 years1.4–2.6–5.417.611.4–23.837.629.8–45.3
36 years6.02.3–9.714.38.6–20.027.520.4–34.7
39 years7.43.6–11.118.312.5–24.138.731.4–45.9
42 years7.03.4–10.718.312.6–24.031.624.5–38.6
45 years11.97.9–15.921.415.2–27.528.320.6–35.9
Parental occupational class in 1980      
Upper non-manual3.5−0.1–7.212.77.0–18.429.522.5–36.6
Lower non-manual6.13.6–8.517.213.4–21.034.329.5–39.0
Manuals (upper or lower)6.43.5–9.417.112.5–21.631.726.0–37.3
Farmers10.66.5–14.823.817.4–30.335.127.0–43.2
Parental education in 1980      
Less than 9 years7.44.6–10.118.013.7–22.233.328.1–38.6
9–12 years7.24.7–9.719.715.8–23.633.228.4–38.1
More than 12 years3.90.8–6.912.98.2–17.731.525.6–37.4
Family income level in 1980      
Low7.34.2–10.419.114.3–24.034.628.6–40.6
Intermediate7.45.2–9.517.914.6–21.233.829.7–37.9
High2.8–0.5–6.113.98.7–19.028.422.1–34.8
Own education in 2007      
Low (comprehensive school)5.6–1.0–12.130.420.2–40.538.025.2–50.8
Intermediate (secondary level, non-academic)6.54.7–8.419.716.8–22.533.129.6–36.7
High education (academic level)6.02.7–9.36.91.9–11.930.624.3–36.8
Social mobility (1980–2007)      
Stable high position2.7–1.9–7.23.7–3.3–10.728.820.0–37.6
Upward mobility9.54.8–14.210.23.1–17.332.423.4–41.4
Downward mobility4.80.8–8.920.113.9–26.433.625.7–41.4
Stable lower position (low/intermediate level)6.94.9–8.920.517.5–23.633.529.6–37.3

Associations between childhood socio-economic position and LBP outcomes

Logistic regression analyses confirmed the contribution of childhood socio-economic circumstances to LBP (Tables 4-6). After adjusting for age (Table 4, Model 1), having been raised in a farm was associated with sciatica among men (OR 3.46, 95% CI 1.21–9.89). The association remained unaffected after adjustments (Models 2 and 3). Additionally, after adjusting for age, women (OR 0.54, 95% CI 0.30–0.98) and men (OR 0.37, 95% CI 0.14–0.96) from high-income families were less likely to report sciatica at follow-up as compared with those women and men who were from low-income families. Adjustments had negligible effects on this association among men, while among women, the association attenuated. Associations between own education and sciatica could not be confirmed.

Table 4. Associations between childhood and adult socio-economic circumstances and sciatica. Odds ratios (OR) and their 95% confidence intervals (CI) among women (n = 1146) and men (n = 944)
Socio-economic circumstancesWomen (n = 1146)Men (n = 944)
Model 1: Adjusted for ageModel 2: Model 1 + parental smoking and BMI adjusted forModel 3: Model 2 + own education adjusted forModel 1: Adjusted for ageModel 2: Model 1 + parental smoking and BMI adjusted forModel 3: Model 2 + own education adjusted for
OR95% CIOR95% CIOR95% CIOR95% CIOR95% CIOR95% CI
  1. Statistically significant associations are marked using a boldface font.

  2. BMI, body mass index.

Parental occupational class in 1980            
Upper non-manual1.00 1.00 1.00 1.00 1.00 1.00 
Lower non-manual1.330.71–2.471.310.70–2.441.220.65–2.311.960.73–5.272.040.76–5.492.140.77–5.96
Manuals (upper or lower)1.830.96–3.491.780.93–3.411.600.82–3.132.070.75–5.742.210.79–6.172.340.80–6.79
Farmers0.920.41–2.080.880.38–2.020.800.34–1.873.461.21–9.893.491.21–10.073.731.23–11.25
Parental education in 1980            
Less than 9 years1.00 1.00 1.00 1.00 1.00 1.00 
9–12 years0.880.57–1.370.890.57–1.400.920.59–1.441.000.56–1.790.990.55–1.800.980.54–1.78
More than 12 years0.700.40–1.220.710.40–1.250.790.44–1.410.480.21–1.090.460.20–1.070.450.19–1.07
Family income level in 1980            
Low1.00 1.00 1.00 1.00 1.00 1.00 
Intermediate0.820.53–1.270.820.52–1.270.830.53–1.301.020.56–1.851.030.56–1.871.020.56–1.86
 High0.540.30–0.980.550.30–1.000.590.32–1.080.370.14–0.960.360.14–0.940.350.13–0.93
Own education in 2007            
Low (comprehensive school)1.00     1.00     
Intermediate (secondary level, non-academic)0.890.34–2.35    1.250.37–4.20    
High education (academic level)0.620.22–1.73    1.100.30–4.08    
Table 5. Associations between childhood and adult socio-economic circumstances and radiating low back pain. Odds ratios (OR) and their 95% confidence intervals (CI) among women (n = 1146) and men (n = 947)
Socio-economic circumstancesWomen (n = 1146)Men (n = 947)
Model 1: Adjusted for ageModel 2: Model 1 + parental smoking and BMI adjusted forModel 3: Model 2 + own education adjusted forModel 1: Adjusted for ageModel 2: Model 1 + parental smoking and BMI adjusted forModel 3: Model 2 + own education adjusted for
OR95% CIOR95% CIOR95% CIOR95% CIOR95% CIOR95% CI
  1. Statistically significant associations are marked using a boldface font.

  2. BMI, body mass index.

Parental occupational class in 1980            
Upper non-manual1.00 1.00 1.00 1.00 1.00 1.00 
Lower non-manual1.480.93–2.351.460.92–2.321.210.75–1.951.430.84–2.431.420.83–2.411.000.57–1.74
Manuals (upper or lower)1.741.06–2.841.661.01–2.721.260.75–2.101.420.81–2.491.380.79–2.430.920.51–1.66
Farmers1.270.71–2.271.220.67–2.220.950.52–1.772.151.17–3.972.151.16–3.991.380.72–2.63
Parental education in 1980            
Less than 9 years1.00 1.00 1.00 1.00 1.00 1.00 
9–12 years1.160.83–1.611.190.85–1.671.270.90–1.791.100.75–1.631.150.77–1.721.310.87–1.97
More than 12 years0.630.41–0.970.660.42–1.020.820.52–1.290.670.41–1.080.710.43–1.161.020.61–1.70
Family income level in 1980            
Low1.00 1.00 1.00 1.00 1.00 1.00 
Intermediate0.810.57–1.130.810.57–1.140.850.60–1.200.920.61–1.360.900.60–1.340.990.66–1.49
High0.540.35–0.840.560.35–0.880.670.42–1.060.680.41–1.130.660.39–1.110.900.53–1.54
Own education in 2007            
Low (comprehensive school)1.00     1.00     
Intermediate (secondary level, non-academic)1.060.50–2.27    0.550.30–1.03    
High education (academic level)0.430.19–0.98    0.170.08–0.38    
Table 6. Associations between childhood and adult socio-economic circumstances and non-specific low back pain. Odds ratios (OR) and their 95% confidence intervals (CI) among women (n = 1132) and men (n = 947)
Socio-economic circumstancesWomen (n = 1132)Men (n = 947)
Model 1: Adjusted for ageModel 2: Model 1 + parental smoking and BMI adjusted forModel 3: Model 2 + own education adjusted forModel 1: Adjusted for ageModel 2: Model 1 + parental smoking and BMI adjusted forModel 3: Model 2 + own education adjusted for
OR95% CIOR95% CIOR95% CIOR95% CIOR95% CIOR95% CI
  1. Statistically significant associations are marked using a boldface font.

  2. BMI, body mass index.

Parental occupational class in 1980            
Upper non-manual1.00 1.00 1.00 1.00 1.00 1.00 
Lower non-manual1.050.74–1.481.020.72–1.450.960.67–1.361.240.84–1.841.240.83–1.831.200.80–1.81
Manuals (upper or lower)1.130.77–1.641.090.75–1.600.990.67–1.481.120.74–1.711.100.72–1.681.060.68–1.66
Farmers0.570.35–0.910.540.33–0.880.500.30–0.821.280.78–2.101.320.80–2.171.270.75–2.14
Parental education in 1980            
Less than 9 years1.00 1.00 1.00 1.00 1.00 1.00 
9–12 years1.170.88–1.551.190.89–1.591.220.91–1.630.960.70–1.330.960.69–1.330.980.70–1.36
More than 12 years1.110.80–1.551.140.82–1.601.240.87–1.760.880.61–1.270.890.61–1.290.930.62–1.37
Family income level in 1980            
Low1.00 1.00 1.00 1.00 1.00 1.00 
Intermediate0.900.67–1.210.890.67–1.200.910.68–1.220.970.70–1.340.940.68–1.310.950.68–1.32
High0.920.65–1.310.920.64–1.320.980.68–1.410.740.49–1.110.720.48–1.080.730.48–1.12
Own education in 2007            
Low (comprehensive school)1.00     1.00     
Intermediate (secondary level, non-academic)1.330.66–2.68    0.780.43–1.39    
High education (academic level)1.010.49–2.09    0.700.37–1.32    

Parental occupational class and family income had similar effects on radiating LBP (Table 5) as those found for sciatica. However, the associations were somewhat weaker. High parental education was inversely associated with radiating LBP among women, but also this association was reduced after own education was adjusted for. After adjusting for age, high own education was inversely associated with radiating LBP among women (OR 0.43, 95% CI 0.19–0.98) and men (OR 0.17, 95% CI 0.08–0.38). Moreover, the associations between the indicators of childhood socio-economic position and radiating LBP were suggested to be mediated via own education. More specifically, the associations between parental education, family income and radiating LBP were partly mediated by own education among women and men, and fully mediated regarding occupational class among men (Table 5, Models 1–3).

Socio-economic differences in non-specific LBP were non-existent. However, women who were from farming families were less likely to have non-specific LBP (Table 6). Thus, after adjusting for age (Model 1), women who had been raised in a farm had lower odds for non-specific LBP (OR 0.57, 95% CI 0.35–0.91). This association slightly strengthened after adjustments.

Social mobility and LBP outcomes

After adjusting for age (Table 7, Model 1), stable lower socio-economic position was associated with radiating LBP among women (OR 3.36, 95% CI 1.77–6.38) and men (OR 7.05, 95% CI 2.55–19.52). Similar associations were observed for downward mobility among women (OR 2.30, 95% CI 1.08–4.88) and men (OR 6.48, 95% CI 2.20–19.15). Adjustments for covariates had minor effects on these associations. For sciatica, similar patterns were suggested among men, but statistical significance was not reached. Additionally, upward mobility was associated with sciatica among men. No associations were found for non-specific LBP.

Table 7. Associations between social mobility and low back pain outcomes. Odds ratios (OR) and their 95% confidence intervals (CI) among women (n = 1204) and men (n = 980)
Socio-economic circumstancesWomen (n = 1204)Men (n = 980)
Model 1: Adjusted for ageModel 2: Model 1 + parental smoking and BMI adjusted forModel 1: Adjusted for ageModel 2: Model 1 + parental smoking and BMI adjusted for
OR95% CIOR95% CIOR95% CIOR95% CI
  1. Statistically significant associations are marked using a boldface font.

  2. BMI, body mass index.

Sciatica        
Stable high position1.00 1.00 1.00 1.00 
Upward mobility0.900.38–2.090.900.39–2.115.081.08–23.885.221.11–24.62
Downward mobility0.920.37–2.290.910.36–2.272.500.49–12.682.570.51–13.06
Stable lower position (low/intermediate level)1.480.75–2.951.480.74–2.953.850.92–16.184.060.96–17.16
Radiating low back pain        
Stable high position1.00 1.00 1.00 1.00 
Upward mobility1.470.69–3.131.460.69–3.122.960.91–9.642.860.88–9.32
Downward mobility2.301.08–4.882.291.08–4.866.482.20–19.156.332.14–18.70
Stable lower position (low/intermediate level)3.361.77–6.383.251.71–6.207.052.55–19.526.752.43–18.75
Non-specific low back pain        
Stable high position1.00 1.00 1.00 1.00 
Upward mobility0.660.41–1.060.670.42–1.071.150.64–2.041.140.64–2.03
Downward mobility0.920.56–1.490.910.56–1.491.200.70–2.041.180.69–2.02
Stable lower position (low/intermediate level)1.040.71–1.531.030.70–1.511.270.82–1.981.260.80–1.97

Discussion

  1. Top of page
  2. Abstract
  3. What's already known about this topic?
  4. What does this study add?
  5. Introduction
  6. Materials and methods
  7. Results
  8. Discussion
  9. Author contributions
  10. Acknowledgements
  11. References

Main findings

This study sought to examine the associations between childhood and current socio-economic position, social mobility and LBP outcomes. The main findings suggest, first that low parental socio-economic position remains a risk factor for radiating LBP and sciatica even after taking into account own education. Second, own education had the most consistent associations with radiating LBP. Third, stable lower socio-economic position and downward mobility are strongly associated with radiating LBP particularly among men.

Interpretation

These results confirm the importance of life-course epidemiology in understanding social inequalities in health (Ben-Shlomo and Kuh, 2002; Kuh and Ben-Shlomo, 2004; Kuh et al., 2005; Power et al., 2007). Adverse childhood conditions have been assumed to affect health in adulthood directly (latency model) or indirectly through adult conditions (pathway model), or to have cumulative effects together with circumstances in adulthood (cumulative model) (Ben-Shlomo and Kuh, 2002; Kuh and Ben-Shlomo, 2004; Kuh et al., 2005). In this study, we focused on the latency and cumulative models.

Studies focusing on life-course socio-economic differences in LBP are almost non-existent, and a study among young British adults failed to find an association between manual social class at birth and LBP in early adulthood (Power et al., 2001). However, adverse childhood conditions have been associated with poor physical functioning (Mäkinen et al., 2006) and disability retirement (Harkonmäki et al., 2007). Childhood socio-economic circumstances such as family income reflect, e.g., childhood living conditions and affect morbidity in adulthood independent of adult socio-economic position (Galobardes et al., 2004). Although childhood and adult circumstances can be distinct dimensions, their effects on health in adulthood have both been shown to persist (Hertzman et al., 2001). It is therefore necessary to simultaneously focus on childhood and current circumstances when examining socio-economic inequalities in health. Our results are in accordance with the earlier evidence and support both the latency and the cumulative models, albeit the associations varied by different socio-economic indicators and types of LBP.

Gender difference with respect to having been raised in a farming environment as a risk factor for low back disorders was clear in our study. While girls may have helped more in household activities, boys who were raised in a farm may have participated in the fieldwork with heavy lifting and other physically demanding tasks. These results suggest that early exposures to physically strenuous work may adversely affect the spine and contribute to low back disorders at follow-up. Long-term effects of early exposures have been proposed also previously (Boshuizen et al., 1990).

Although our findings confirmed the association between own education and back pain (Latza et al., 2000), we focused on the associations between childhood socio-economic position and LBP outcomes that remained independent of own education. Additionally, the importance of social mobility needs to be highlighted as the risk of radiating LBP was particularly high among those with stable lower socio-economic position and downward social mobility as measured by educational level of participants and their parents. A recent study found that stable low socio-economic position was associated with pain interfering with work (Lacey et al., 2013). However, childhood socio-economic position in that study was retrospective and based on age when the respondent left school, the study included only older participants and pain was based on a single item. Albeit using a different socio-economic indicator, our findings are further in line with earlier evidence showing that those with stable manual class tend to have poorer physical health (Power et al., 2007) and higher mortality (Hart et al., 1998).

It is plausible that persistent adverse socio-economic circumstances show the strongest associations. One might also assume mobility from low to higher social position (high education) to be protective of low back disorders, e.g., via moving to a job with lower physical demands and better job control; however, this was not found in our study. It is possible that the association between upward social mobility and increased risk of sciatica among men in our study is a chance finding due to a very small number of men in this particular group. Alternatively, early life harmful exposures might also continue to affect the later risk of sciatica also among men with upward social mobility, suggesting long latency.

Childhood socio-economic differences were found for radiating LBP and sciatica. Three groups of risk factors exerting their effects via different pathophysiological pathways could be suggested. These include physical load (biomechanical pathway), health behaviours (mainly via a metabolic pathway) and psychosocial factors (perception of symptoms, coping, etc.). Early physical exposures may cause damage to the spine, inducing a degenerative process and lead to radiating LBP or sciatica. Additionally, those with lower socio-economic position can be more prone to accidental injuries (Laflamme et al., 2009) that again might lead to degeneration and increased risk of low back disorders. Those with lower socio-economic position are also more likely to smoke as well as be physically inactive and overweight. Smoking and overweight have also been identified as risk factors of LBP (Leboeuf-Yde, 1999, 2000; Shiri et al., 2010a). As our outcomes were self-reported, contribution of psychosocial factors cannot be ruled out (Schneider et al., 2005). For example, perception of pain could differ between socio-economic groups. Women also tend to report more symptoms than men (Schneider et al., 2006).

Finally, low back disorders are prevalent and a major cause of work disability (Hagen et al., 2000; Griffith et al., 2012; Saastamoinen et al., 2012). This highlights the societal and public health significance of novel evidence about the determinants of such disorders in childhood and early adulthood. Furthermore, to help employees maintain their work ability, it is important to identify the risk groups for different types of LBP, tackle their causes at an early phase, and promote health and well-being of employed populations and young people entering the labour market.

Methodological considerations

This study had some limitations. First, LBP outcomes were self-reported. However, pain is a subjective condition, and most epidemiological studies rely on self-reported data (Dionne, 2010). Second, the numbers did not allow for a more detailed analysis of critical and sensitive periods by examining different age cohorts. Future studies could elaborate the sensitive periods and conduct the analyses in different age strata. Third, additional indicators of own socio-economic position such as occupational class and income could shed light on the persistence and course of socio-economic inequalities in LBP. However, in this cohort of young adults, education was considered as the most suitable indicator of socio-economic position. Fourth, childhood pain could also be related to experience of pain in adulthood (Macfarlane, 2010) and this was not assessed in this study. Further elaboration of mediating factors such as own BMI, smoking, and other health behaviours or physical workload was beyond the scope of this study and could be addressed in further studies.

Strengths of the study include a long follow-up of women and men from childhood and adolescence to young adulthood and early middle age. Childhood socio-economic data were based on reports from baseline and thus not sensitive to bias typical to prior studies using retrospective data on childhood socio-economic position (Hardt and Rutter, 2004). Additionally, multiple socio-economic circumstances were examined to shed light on their independent effects. This is of importance as various indicators of socio-economic position are not interchangeable but capture different domains of socio-economic circumstances (Braveman et al., 2005). The opportunity to include own education is a special strength, as we could examine both the independent, direct effects of childhood socio-economic position to LBP outcomes and mediating effects of own education. The inclusion of own education also provided the opportunity to examine social mobility using parental and own education to indicate changes and stability in socio-economic position across life course. A further strength is the inclusion of different LBP outcomes, as many previous studies have only focused on non-specific or any back pain. We not only distinguished between the two main types of LBP, non-specific and radiating LBP, but also studied a clinically defined low back disorder, i.e., sciatica. Focus on these two types of LBP and sciatica helped increase understanding whether they share similar or different risk factors across life course, and highlighted the need to separate non-specific LBP from specific low back disorders.

Conclusions

Childhood socio-economic position contributes to low back disorders in adults. The associations, however, vary for different LBP outcomes and by socio-economic indicator. The found associations remained after considering own education and potential confounders, suggesting that low back disorders have early origins in childhood families and exposures in particular in children with low socio-economic position. Own education contributes to particularly the risk of radiating LBP. Additionally, stable lower socio-economic position and downward social mobility as measured by education are risk factors for radiating LBP. Gender differences likely reflect different exposures and differences in life-course risk factor trajectories among women and men. To prevent low back disorders, childhood socio-economic circumstances, cumulative adversity and long latency of early exposures should be considered.

Author contributions

  1. Top of page
  2. Abstract
  3. What's already known about this topic?
  4. What does this study add?
  5. Introduction
  6. Materials and methods
  7. Results
  8. Discussion
  9. Author contributions
  10. Acknowledgements
  11. References

T.L. contributed to conception and design of the study, conducted the analyses, interpreted the data and drafted the first version of the article. E.V.-J. and S.S. helped plan the study design and the analyses. All authors discussed the results and commented on the manuscript, and approved submission of the final version.

Acknowledgements

  1. Top of page
  2. Abstract
  3. What's already known about this topic?
  4. What does this study add?
  5. Introduction
  6. Materials and methods
  7. Results
  8. Discussion
  9. Author contributions
  10. Acknowledgements
  11. References

The expert technical assistance in data management by Irina Lisinen and Ville Aalto is gratefully acknowledged.

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  3. What's already known about this topic?
  4. What does this study add?
  5. Introduction
  6. Materials and methods
  7. Results
  8. Discussion
  9. Author contributions
  10. Acknowledgements
  11. References
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