Menopausal hormone therapy, oral contraceptives and risk of chronic low back pain: the HUNT Study.

BACKGROUND: There are indications that use of menopausal hormone therapy (MHT) and oral contraceptives (OC) increases the risk of low back pain (LBP), with higher oestrogen levels involved in the underlying mechanisms. The purpose of the present study was to investigate associations between use of systemic MHT or OC and risk of chronic LBP in a large population-based data set. METHODS: Data were obtained from two surveys in the Trøndelag Health Study in Norway, HUNT2 (1995-1997) and HUNT3 (2006-2008). A cross-sectional study of association between use of systemic MHT and prevalence of chronic LBP comprised 12,974 women aged 40-69 years in HUNT2, with 4007 women reporting chronic LBP. A cohort study involving MHT comprised 6007 women without chronic LBP at baseline in HUNT2, and after 11 years 1245 women reported chronic LBP at follow-up in HUNT3. The cross-sectional study of association with use of OC included 23,593 women aged 20-69 years in HUNT2, with 6085 women reporting chronic LBP. The corresponding cohort study included 10,586 women without chronic LBP at baseline in HUNT2, of whom 2084 women reported chronic LBP in HUNT3. Risk of chronic LBP was examined in both study designs in generalised linear models with adjustment for potential confounders. RESULTS: In the cohort study, current users of systemic MHT at baseline showed a greater risk of chronic LBP (relative risk (RR) 1.30; 95% CI: 1.14-1.49; compared with never users). The risk increased according to duration of MHT use (P for linear trend = 0.003). Known users of systemic MHT based exclusively on oestrogen experienced the highest risk (RR 1.49; 95% CI: 1.16-1.91), but an increased risk was also seen among known users of oestrogen-progestin combination MHT (RR 1.35; 95% CI: 1.16-1.57). A slight increase in risk of chronic LBP was found in the cohort study among former users of OC (RR 1.17; 95% CI: 1.06-1.30; compared with never users). CONCLUSIONS: Long-lasting use of systemic MHT, in particular therapy based on oestrogen only, is associated with greater risk of chronic LBP. Having been a user of OC most likely entails a minor increase in risk.

The association between insomnia, c-reactive protein, and chronic low back pain: cross-sectional analysis of the HUNT study, Norway.

BACKGROUND AND AIMS: Chronic low back pain (chronic LBP) is the number one cause for years lived with disability among 301 diseases and injuries analyzed by The Global Burden of Disease study 2013. Insomnia is highly prevalent among people with chronic LBP. To explain the sleep-pain relationship, theoretical models propose that insomnia symptoms may be associated with increased basal inflammation, operationalized as c-reactive protein (CRP) and lead to further pain and disrupted sleep. We aimed to determine the associations between insomnia, chronic LBP, and inflammation (operationalized as CRP), whilst controlling for age, body mass index, smoking, physical activity, depression, anxiety and osteoarthritis. METHODS: A cross-sectional analysis of the third Nord-Trøndelag Health Study (2006-2008), a rural population survey of 50,666 participants in Norway aged 20-96 years. Insomnia (dichotomous) was defined according to the Diagnostic and Statistical Manual of Mental Disorders 5th Edition, and chronic LBP (dichotomous) as low back pain or stiffness lasting at least 3 months. Data for CRP were obtained from non-fasting serum samples and assessed via latex immunoassay methodology. We excluded participants with the following self-reported chronic somatic diseases: chronic heart failure, chronic obstructive pulmonary disease, rheumatoid arthritis, fibromyalgia or ankylosing spondylosis. Possible associations between presence of insomnia and presence of chronic LBP (dependent), and the level of CRP and presence of chronic LBP (dependent), were assessed using logistic regression models. The possible association between insomnia and CRP (dependent) was assessed using linear regression. Multivariable analyses were conducted adjusting for confounders stated in our aim that achieved p ≤ 0.2 in univariate regressions. We performed stratified analyses for participants with "Normal" (<3 mg/L) "Elevated" (3-10 mg/L) and "Very High" (>10 mg/L) levels of CRP. RESULTS: In our total included sample (n = 30,669, median age 52.6, 54% female), 6.1% had insomnia (n = 1,871), 21.4% had chronic LBP (n = 6,559), and 2.4% had both (n = 719). Twenty four thousand two hundred eighty-eight (79%) participants had "Normal" CRP, 5,275 (17%) had "Elevated" CRP, and 1,136 (4%) had "Very High" CRP. For participants with "Normal" levels of CRP, insomnia was associated with higher levels of CRP (adjusted B = 0.04, 95%CI [0.00-0.08], p = 0.046), but not for people with "Elevated" or "Very High" levels of CRP. There was an association between CRP and presence of chronic LBP in the total sample (adjusted OR = 1.01, [1.00-1.01], p = 0.013) and for people with "Normal" CRP (1.05, [1.00-1.10, p = 0.034]. Insomnia was associated with the presence of chronic LBP in the total sample (adjusted OR = 1.99, 95%CI [1.79-2.21], <0.001) and for people with "Normal", "Elevated" and "Very High". CONCLUSIONS: Individuals with insomnia have twice the odds of reporting chronic LBP. Insomnia, CRP and chronic LBP appear to be linked but the role of CRP appears to be limited. Longitudinal studies may help further explore the causal inference between insomnia chronic LBP, and inflammation. IMPLICATIONS: Given the strong relationship between insomnia and chronic LBP, screening and management of comorbid insomnia and chronic LBP should be considered in clinical practice. Further longitudinal studies are required to explore whether the presence of insomnia and increased inflammation affects the development of chronic LBP.

Is chronic low back pain a risk factor for diabetes? The Nord-Trøndelag Health Study.

OBJECTIVE: The purpose of this study was to examine the risk of diabetes associated with the presence or absence of chronic low back pain, considering both cross-sectional and cohort data. RESEARCH DESIGN AND METHODS: Analyses were based on the Norwegian HUNT2 and HUNT3 surveys of Nord-Trøndelag County. The prevalence of diabetes was compared in groups with and without chronic low back pain among 45 157 participants aged 30-69 years. Associations between low back pain at baseline and risk of diabetes were examined in an 11-year follow-up of 30 380 individuals with no baseline diagnosis of diabetes. The comorbidity between diabetes and low back pain was assessed at the end of follow-up. All analyses were carried out considering generalized linear models incorporating adjustment for other relevant risk factors. RESULTS: Cross-sectional analyses did not reveal any association between low back pain and diabetes. With adjustment for age, body mass index, physical activity and smoking, the cohort study of women showed a significant association between low back pain at baseline and risk of diabetes (RR 1.30; 95% CI 1.09 to 1.54, p=0.003). The association differed between age groups (p=0.015), with a stronger association in relatively young women. In men, no association was found in the whole age range (RR 1.02; 95% CI 0.86 to 1.21, p=0.82). No association was observed between diabetes and chronic low back pain at the end of follow-up. CONCLUSION: Among younger women, those with chronic low back pain may have an increased risk of diabetes.

Lifestyle factors and risk of migraine and tension-type headache. Follow-up data from the Nord-Trøndelag Health Surveys 1995-1997 and 2006-2008.

AIMS: The aim of this population-based historical cohort study was to investigate the influence of lifestyle factors on the risk of developing migraine or tension-type headache (TTH). METHODS: Data from the Nord-Trøndelag Health Study performed in 1995-1997 and 2006-2008 was used. A total of 15,276 participants without headache at baseline were included. A Poisson regression was used to evaluate the associations between lifestyle factors and risk ratios (RRs) of migraine and TTH 11 years later. Precision of the estimates was assessed by 95% confidence interval (CIs). RESULTS: Increased risk of migraine (RR 1.30, 95% CI 1.11-1.52) was found in smokers (past or current) compared to those who had never smoked. Hard physical exercise 1-2 hours per week reduced the risk of migraine (OR 0.71, 95% CI 0.54-0.94) compared to inactivity, and the risk of migraine was also lower among those who consumed alcohol (RR 0.73, 95% CI 0.57-0.94) compared to abstainers. No association was found between smoking, physical activity, alcohol use and risk of TTH. CONCLUSIONS: The main finding was that current and previous smoking was associated with increased risk of migraine, but not of TTH.

Is there an association between vitamin D status and risk of chronic low back pain? A nested case-control analysis in the Nord-Trøndelag Health Study.

OBJECTIVES: To explore potential associations between vitamin D status and risk of chronic low back pain (LBP) in a Norwegian cohort, and to investigate whether relationships depend on the season of blood sample collection. DESIGN: A nested case-control study in a prospective data set. SETTING: The Norwegian community-based Nord-Trøndelag Health Study (HUNT). Data were collected in the HUNT2 (1995-1997) and HUNT3 (2006-2008) surveys. MAIN OUTCOME MEASURE: Chronic LBP, defined as LBP persisting at least 3 months continuously during the past year. PARTICIPANTS: Among individuals aged 19-55 years without LBP in HUNT2, a data set was generated including 1685 cases with LBP in HUNT3 and 3137 controls without LBP. METHODS: Blood samples from the participants collected in HUNT2 were analysed for serum 25-hydroxyvitamin D (25(OH)D) level. Associations with LBP in HUNT3 were evaluated by unconditional logistic regression analysis with adjustment for age, sex, work status, physical activity at work and in leisure time, education, smoking, and body mass index. RESULTS: No association between vitamin D status and risk of chronic LBP was found in the total data set (OR per 10 nmol/L 25(OH)D=1.01, 95% CI 0.97 to 1.06) or in individuals with blood samples collected in summer/autumn (OR per 10 nmol/L 25(OH)D=0.99, 95% CI 0.93 to 1.06). For blood samples drawn in winter/spring, associations differed significantly between women and men (p=0.004). Among women a positive association was seen (OR per 10 nmol/L 25(OH)D=1.11, 95% CI 1.02 to 1.20), but among men no significant association was observed (OR per 10 nmol/L 25(OH)D=0.90, 95% CI 0.81 to 1.01). CONCLUSIONS: Overall, no association between vitamin D status and risk of LBP was demonstrated. The association suggested in women for the winter/spring season cannot be regarded as established.

Physical activity level at work and risk of chronic low back pain: A follow-up in the Nord-Trøndelag Health Study.

BACKGROUND: Physical activity in leisure time seems to reduce the risk of low back pain, but it is not known whether occupational activity, as recorded in a representative working population, produces a higher or lower risk. OBJECTIVE: To study associations between physical activity level at work and risk of chronic low back pain. METHODS: Associations were examined in a Norwegian prospective study using data from the HUNT2 and HUNT3 surveys carried out in the whole county of Nord-Trøndelag. Participants were 7580 women and 7335 men who supplied information about physical activity level at work. Levels considered were sedentary work, work involving walking but no heavy lifting, work involving walking and heavy lifting, and particularly strenuous physical work. Nobody in the cohort was affected by chronic low back pain at baseline. After 11 years, participants reported whether they suffered from chronic low back pain. Generalized linear modelling with adjustment for potential confounders was applied to assess associations with risk factors. RESULTS: In age-adjusted analyses both women and men showed statistically significant associations between physical activity at work and risk of chronic low back pain, suggesting positive relationships. For particularly strenuous physical work the relative risk of chronic low back pain was 1.30 (95% CI: 1.00-1.71) in women and 1.36 (95% CI 1.17-1.59) in men, compared to sedentary work. Women still showed a general association with activity level after adjustment for education, leisure time physical activity, BMI, smoking and occupational category. In men, the higher risk was only maintained for particularly strenuous work. CONCLUSION: In this cohort, women had a higher risk of chronic low back pain with work involving walking and heavy lifting or particularly strenuous work, compared to sedentary work. Men participating in particularly strenuous work also experienced a higher risk of chronic low back pain.

The Mortality Associated With Chronic Widespread Musculoskeletal Complaints: A Systematic Review of the Literature.

BACKGROUND: Chronic widespread musculoskeletal complaints (CWMSC) are a prevalent condition with a large impact on quality of life and with a large burden on society. Studies investigating the relationship between CWMSC and mortality have yielded inconsistent results. The present study aimed to clarify this relationship through a systematic review of the existing literature, including meta-analyses, to estimate pooled results and heterogeneity. METHODS: The MEDLINE, EMBASE and Science Citation Index Expanded databases were searched in February 2016. Broad search terms were used to identify as many observational studies as possible that investigated the association between CWMSC and mortality. The identified studies were evaluated according to predetermined inclusion criteria. RESULTS: Six studies fulfilled the inclusion criteria. In pooled unadjusted analyses of three studies evaluating CWMSC, a non-significant tendency of increased overall mortality was found [mortality risk ratio (MRR) 1.69, 95% confidence interval (CI) 0.91-3.14]. However, in pooled analyses of all six studies reporting adjusted results, the non-significant tendency for higher mortality rates in those with CWMSC was nearly eliminated (MRR 1.13, 95% CI 0.95-1.34). Heterogeneity between studies was moderate to high, particularly regarding the use of confounding factors. CONCLUSIONS: In this systematic review, based on a limited number of studies, pooled data gave no evidence of a higher mortality rate among individuals with CWMSC. The non-significant tendency for a higher mortality rate in unadjusted pooled analyses was nearly eliminated in the adjusted pooled analyses, considering lifestyle factors such as physical activity smoking. In population-based studies evaluating the relationship between CWMSC and mortality rates, we recommend that both unadjusted and adjusted analyses should be presented. Copyright © 2016 John Wiley & Sons, Ltd.

Is there a U-shaped relationship between physical activity in leisure time and risk of chronic low back pain? A follow-up in the HUNT Study.

BACKGROUND: Physical activity in leisure time is often considered to have favourable effects on the risk of low back pain (LBP), but demonstrating a definite association in epidemiological studies has proven difficult. The purpose of the present study was to explore associations between physical activity and risk of chronic LBP in an adult population and to investigate whether relationships are limited to certain age groups or to females or males. A particular objective was to determine whether support could be found for a U-shaped relationship, with both low and high activity levels carrying greater risk. METHODS: The relationship between physical activity and risk of chronic LBP was examined in a Norwegian prospective study using data from the community-based HUNT2 and HUNT3 surveys. Participants were 9616 women and 8452 men without LBP at baseline, who reported after 11 years whether they suffered from LBP. Associations between baseline physical activity in leisure time and risk of chronic LBP at end of follow-up were evaluated by generalized linear modelling with adjustment for potential confounders. RESULTS: Significant associations between leisure time physical activity and risk were observed in both sexes after age adjustment, mainly suggesting inverse relationships. Women participating in hard physical activity 1-2 h per week had a relative risk (RR) of chronic LBP of 0.81 (95 % CI 0.71-0.93) compared to those with only light physical activity less than 1 h per week. The corresponding RR in men was 0.71 (95 % CI 0.60-0.85). After adjustment for education, employment, occupational activity, body mass index (BMI) and smoking, significant relationships could only be demonstrated in those aged 50 years or more at baseline. The associations differed between female educational groups, with more U-shaped relationships being observed among women with basic education only. CONCLUSION: No strong support was found overall for U-shaped relationships. However, no further general decrease in risk was seen among those with 3 h or more of hard physical activity per week. The contrasts observed between female educational groups may reflect different preferences regarding specific strenuous activities. Men aged 50 years or more seem in particular to benefit from hard physical activities.

Chronic musculoskeletal complaints as a predictor of mortality-The HUNT study.

The impact of chronic musculoskeletal complaints (CMSC) and chronic widespread chronic musculoskeletal complaints (CWMSC) on mortality is controversial. The aim of this study was to investigate the relationship between these conditions and mortality. In this prospective population-based cohort study from Norway, baseline data from the second Nord-Trøndelag Health Survey (HUNT2, performed 1995-1997) were linked to the comprehensive National Cause of Death Registry in Norway with follow-up through the year 2011. A total of 65,026 individuals (70%) participated and were categorized based on their response to CMSC questions in HUNT2 (no CMSC, CMSC, or CWMSC). Hazard ratios (HRs) of mortality during a mean of 14.1 years of follow-up were estimated using Cox regression. During the follow-up period, 12,521 subjects died, 5162 from cardiovascular diseases, 3478 from cancer, and 3881 from all other causes. In the multivariate-adjusted analyses, there was no difference in all-cause mortality between individuals with or without CMSC (HR 1.01, confidence interval, 0.97-1.05) and CWMSC (HR 1.01, confidence interval, 0.96-1.05). Similarly, there was no association between CMSC or CWMSC and cardiovascular mortality, mortality from cancer, or mortality from all other causes. Therefore, from this study, we conclude that there is no evidence for a higher mortality rate among individuals with CMSC or CWMSC.

A Comparison of Anthropometric Measures for Assessing the Association between Body Size and Risk of Chronic Low Back Pain: The HUNT Study.

BACKGROUND: Previous work indicates that overweight and obese individuals carry an increased risk of experiencing chronic low back pain (LBP). It is not known, however, how the association with body size depends on the choice of anthropometric measure used. OBJECTIVE: This work compares relationships with LBP for several measures of body size. Different results may indicate underlying mechanisms for the association between body size and risk of LBP. METHODS: In a cohort study, baseline information was collected in the community-based HUNT2 (1995-1997) and HUNT3 (2006-2008) surveys in Norway. Participants were 10,059 women and 8725 men aged 30-69 years without LBP, and 3883 women and 2662 men with LBP at baseline. Associations with LBP at end of follow-up were assessed by generalized linear modeling, with adjustment for potential confounders. RESULTS: Relationships between waist-hip-ratio and occurrence of LBP at end of follow-up were weak and non-significant after adjustment for age, education, work status, physical activity, smoking, lipid levels and blood pressure. Positive associations with LBP at end of follow-up were all significant for body weight, BMI, waist circumference and hip circumference after similar adjustment, both in women without and with LBP at baseline, and in men without LBP at baseline. After additional mutual adjustment for anthropometric measures, the magnitude of the association with body weight increased in women without LBP at baseline (RR: 1.130 per standard deviation, 95% CI: 0.995-1.284) and in men (RR: 1.124, 95% CI 0.976-1.294), with other measures showing weak associations only. CONCLUSION: Central adiposity is unlikely to play a major role in the etiology of LBP. Total fat mass may be one common factor underlying the associations observed. The association with body weight remaining after mutual adjustment may reflect mechanical or structural components behind the relationship between overweight or obesity and LBP.

Association between body height and chronic low back pain: a follow-up in the Nord-Trøndelag Health Study.

OBJECTIVE: To study potential associations between body height and subsequent occurrence of chronic low back pain (LBP). DESIGN: Prospective cohort study. SETTING: The North-Trøndelag Health Study (HUNT). Data were obtained from a whole Norwegian county in the HUNT2 (1995-1997) and HUNT3 (2006-2008) surveys. PARTICIPANTS: Altogether, 3883 women and 2662 men with LBP, and 10,059 women and 8725 men without LBP, aged 30-69 years, were included at baseline and reported after 11 years whether they suffered from LBP. MAIN OUTCOME MEASURE: Chronic LBP, defined as pain persisting for 3 months during the previous year. RESULTS: Associations between body height and risk and recurrence of LBP were evaluated by generalised linear modelling. Potential confounders, such as BMI, age, education, employment, physical activity, smoking, blood pressure and lipid levels were adjusted for. In women with no LBP at baseline and body height ≥ 170 cm, a higher risk of LBP was demonstrated after adjustment for other risk factors (relative risk 1.19, 95% CI 1.03 to 1.37; compared with height <160 cm). No relationship was established among men or among women with LBP at baseline. CONCLUSIONS: In women without LBP, a body height ≥ 170 cm may predispose to chronic LBP 11 years later. This may reflect mechanical issues or indicate a hormonal influence.

Do abnormal serum lipid levels increase the risk of chronic low back pain? The Nord-Trøndelag Health Study.

BACKGROUND: Cross-sectional studies suggest associations between abnormal lipid levels and prevalence of low back pain (LBP), but it is not known if there is any causal relationship. OBJECTIVE: The objective was to determine, in a population-based prospective cohort study, whether there is any relation between levels of total cholesterol, high density lipoprotein (HDL) cholesterol and triglycerides and the probability of experiencing subsequent chronic (LBP), both among individuals with and without LBP at baseline. METHODS: Information was collected in the community-based HUNT 2 (1995-1997) and HUNT 3 (2006-2008) surveys of an entire Norwegian county. Participants were 10,151 women and 8731 men aged 30-69 years, not affected by chronic LBP at baseline, and 3902 women and 2666 men with LBP at baseline. Eleven years later the participants indicated whether they currently suffered from chronic LBP. RESULTS: Among women without LBP at baseline, HDL cholesterol levels were inversely associated and triglyceride levels positively associated with the risk of chronic LBP at end of follow-up in analyses adjusted for age only. Adjustment for the baseline factors education, work status, physical activity, smoking, blood pressure and in particular BMI largely removed these associations (RR: 0.96, 95% CI: 0.85-1.07 per mmol/l of HDL cholesterol; RR: 1.16, 95% CI: 0.94-1.42 per unit of lg(triglycerides)). Total cholesterol levels showed no associations. In women with LBP at baseline and men without LBP at baseline weaker relationships were observed. In men with LBP at baseline, an inverse association with HDL cholesterol remained after complete adjustment (RR: 0.83, 95% CI: 0.72-0.95 per mmol/l). CONCLUSION: Crude associations between lipid levels and risk of subsequent LBP in individuals without current LBP are mainly caused by confounding with body mass. However, an association with low HDL levels may still remain in men who are already affected and possibly experience a higher pain intensity.

Body mass index as a risk factor for developing chronic low back pain: a follow-up in the Nord-Trøndelag Health Study.

STUDY DESIGN: A population-based, prospective cohort study. OBJECTIVE: To determine whether overweight, obesity, or more generally an elevated body mass index (BMI) increase the probability of experiencing chronic low back pain (LBP) after an 11-year period, both among participants with and without LBP at baseline. SUMMARY OF BACKGROUND DATA: Chronic LBP is a common disabling disorder in modern society. Cross-sectional studies suggest an association between an elevated BMI and LBP, but it is not clear whether this is a causal relationship. METHODS: Data were obtained from the community-based HUNT 2 (1995-1997) and HUNT 3 (2006-2008) studies of an entire Norwegian county. Participants were 8733 men and 10,149 women, aged 30 to 69 years, who did not have chronic LBP at baseline, and 2669 men and 3899 women with LBP at baseline. After 11 years, both groups indicated whether they currently had chronic LBP, defined as pain persisting for at least 3 months continuously during the last year. RESULTS: A significant positive association was found between BMI and risk of LBP among persons without LBP at baseline. The odds ratio for BMI 30 or more versus BMI less than 25 was 1.34 (95% confidence interval [CI], 1.08-1.67) for men and 1.22 (95% CI, 1.03-1.46) for women, in analyses adjusted for age, education, work status, physical activity at work and in leisure time, smoking, blood pressure, and serum lipid levels. A significant positive association was also established between BMI and recurrence of LBP among women. LBP status at baseline had negligible influence on subsequent change in BMI. CONCLUSION: High values of BMI may predispose to chronic LBP 11 years later, both in individuals with and without LBP. The association between BMI and LBP is not explained by an effect of LBP on later change in BMI.

Associations between serum lipid levels and chronic low back pain.

BACKGROUND: Low back pain may be related to abnormal lipid levels because of atherosclerosis in arteries supplying the lumbar region. METHODS: In the cross-sectional HUNT 2 study in the Norwegian county of Nord-Trøndelag, lipid levels were measured in 33,962 women and 30,031 men. A total of 8954 women (26%) and 6273 men (21%) reported suffering from low back pain continuously for at least 3 months in the past year. RESULTS: In age-adjusted analyses, the prevalence of low back pain was inversely associated with HDL cholesterol and positively associated with triglycerides, with stronger associations in women than in men. Relatively weak associations remained in women after adjustment for smoking, physical activity, education, work status, blood pressure, and body mass, but no associations remained among men. Total cholesterol levels were unrelated to low back pain in either sex after age adjustment. CONCLUSIONS: The results are partly consistent with the atherosclerosis hypothesis.

The impact of body mass index on the prevalence of low back pain: the HUNT study.

STUDY DESIGN: A cross-sectional population-based study. OBJECTIVE: To examine the association between body mass index and chronic low back pain, with adjustment for potential confounders. SUMMARY OF BACKGROUND DATA: Although many studies have investigated this association, it is still unclear whether there is a general relationship between body mass index and low back pain which applies to all populations. METHODS: This study is based on data collected in the HUNT 2 study in the county of Nord-Trøndelag in Norway between 1995 and 1997. Among a total of 92,936 persons eligible for participation, 30,102 men and 33,866 women gave information on body mass index and indicated whether they suffered from chronic low back pain (69% participation rate). A total of 6293 men (20.9%) and 8923 women (26.3%) experienced chronic low back pain. Relations were assessed by logistic regression of low back pain with respect to body mass index and other variables. RESULTS: In both sexes, a high body mass index was significantly associated with an increased prevalence of low back pain. In men the estimated OR per 5 kg/m increase in body mass index was 1.07 (95% CI: 1.03-1.12) and in women 1.17 (95% CI: 1.14-1.21), after adjustment for age, with a significantly stronger association in women. Additional adjustment for education, smoking status, leisure time physical activity, employment status, and activity at work hardly affected these associations. No interactions were found with most other factors. CONCLUSION: This large population-based study indicates that obesity is associated with a high prevalence of low back pain. Further studies are needed to determine if the association is causal.