LEEST

Eira Viikari-Juntura is Research Professor and Director of the Musculoskeletal Centre within the Finnish Institute of Occupational Health, Helsinki Finland. She is also Team Leader of the Work-Related Disorders Team, Assistant Editor in Chief of the Scandinavian Journal of Work Environment & Health, and senior lecturer at the University of Helsinki. She is MD, PhD and specialist in physical medicine and rehabilitation. She has worked as Visiting Professor at the University of Washington and Professor in Rehabilitation Medicine at Göteborg University and Chief Medical Officer at Sahlgrenska University Hospital in Sweden. Her areas of scientific interest include epidemiology of musculoskeletal disorders, diagnostics and functional capacity assessment, assessment of exposure and intervention studies. She is the founding member and previous Chair of the Scientific Committee for Musculoskeletal Disorders within ICOH.

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LIFESTYLE FACTORS IN MUSCULOSKELETAL DISORDERS (MSDS)− IMPLICATIONS FOR RESEARCH
VIIKARI-JUNTURA E.
Finnish Institute of Occupational Health, Helsinki, Finland

The current understanding is that several individual and environmental factors play a role in the etiology of various MSDs. The presentation will focus on lifestyle factors, such as overweight and obesity, smoking and physical activity and their effects on various musculoskeletal outcomes.

Associations of lifestyle factors with MSDs
One or more lifestyle factors have been taken into consideration in most epidemiological studies on MSDs ; however their independent effects and especially their role in modifying the effects of work environmental factors have been rarely addressed. Moreover, the selected factors and the methods to measure and classify them vary between studies. Consistent understanding on their role has therefore been difficult to obtain and even systematic reviews have sometimes given conflicting results.

Overweight and obesity
The association of overweight and obesity with low back pain (LBP) have been addressed in a number of original studies and one earlier systematic review that have resulted in inconsistent findings. A recent systematic review that evaluated the studies according to four biases (selection, performance, detection, and attrition bias) included 95 studies in the systematic review and 33 studies in meta-analyses. The findings indicated that both overweight and obesity increase the risk of LBP. They had the strongest association with seeking care for LBP and chronic LBP (1). Body mass index (BMI) has been most widely used in studies on obesity and LBP. It has, however, been discussed that BMI may not be an ideal measure of obesity, since it measures both body fat and lean body mass and does not reflect well fat distribution (2). A couple of studies have found that measures of abdominal obesity, such as waist circumference, have shown a stronger association with LBP than BMI. Future studies should use several measures to address weight-related factors. Better indicators of obesity will assist in better understanding the mechanisms behind the associations of obesity with LBP.

Smoking
The associations of smoking and LBP have likewise been inconsistent according to earlier studies. Using similar quality assessment as above, a systematic review included 81 studies, in which 40 were included in meta-analyses. The results showed that both current and former smokers have a higher prevalence and incidence ( Fermer Incidence
Indicateur épidémiologique mesurant la fréquence de survenue d'une maladie pendant une période donnée En savoir plus... ) of LBP than never smokers, but the association was fairly modest. Former smokers had a higher prevalence of LBP compared with never smokers, but a lower prevalence of LBP than current smokers, suggesting that cessation of smoking might prevent LBP. The association between current smoking and the incidence of LBP was stronger in adolescents than in adults, suggesting higher vulnerability of younger subjects to the effects of smoking or less exposure to other risk factors (3).

Physical activity
According to a review published ten years ago, studies on the relationship between leisure time physical exercise and musculoskeletal disorders in worker populations showed inconsistent results (4). Two later reviews addressed the relationship of physical capacity measures (that can be assumed to correlate with physical activity) with low back and neck pain (5) and sedentary lifestyle (as a countermeasure of physical activity) with LBP (6). Low trunk muscle endurance is not a predictor of LBP, and inconsistent results have been found for low back muscle strength and mobility. Sedentary lifestyle does not seem to be associated with LBP. The associations of physical activity with musculoskeletal disorders are a conspicuously difficult topic for an epidemiological approach, since physical activity in general can be expected to have beneficial effects by strengthening the musculoskeletal tissues. However, certain types of activities and sports may have injurious effects, and a systematic review showed that physical activity indeed was associated with increased risk of sciatic pain (7). Furthermore, the interpretation of epidemiological data is difficult, since subjects with musculoskeletal symptoms may either increase or decrease their physical activity as an attempt to alleviate their symptoms. Finally, physical activity and obesity are linked with each other, lack of physical activity leading to obesity and vice versa (8).

Other cardiovascular risk factors
Obesity, smoking and physical inactivity are all risk factors of cardiovascular diseases. Some studies have addressed the association of a wider set of cardiovascular risk factors in low back disorders, including serum lipids. In a representative population sample of males an association was found between measured levels of serum cholesterol (total and LDL cholesterol) and triglycerides with clinically assessed sciatica, allowing for several possible confounders (9). To directly test the association between atherosclerosis and sciatica, a subsample was studied of the Finnish Health 2000 population to whom measurements of carotid artery intima-media thickness (a measure of general atherosclerosis) had been performed by ultrasound. Carotid intima-media thickness was associated with continuous radiating LBP and with a positive unilateral clinical sign of sciatica among men (10). These findings suggest that MSDs and CVDs have common risk factors and may also share common pathomechanical pathways.

Effects of modification of lifestyle factors
While there is evidence from observational epidemiological studies that some lifestyle factors are risk factors of MSDs, what is the evidence from intervention studies in which one or a set of lifestyle factors have been targeted ? There seem to be no well-designed studies to assess the effects of weight reduction or smoking cessation. Lifestyle interventions have typically looked at physiological and cardiovascular outcomes, and few studies have looked at the musculoskeletal system. A multidisciplinary lifestyle intervention study targeted at hypertension looked also at LBP, neck pain and shoulder pain and associated disability. The intervention aimed to reduce hypertension was not effective at reducing prevalence of LBP or disability. However, in the subgroup of persons doing moderate or heavy work, the intervention seemed to reduce prevalence of LBP during the 1-year follow-up (11). There was also an effect on disability due to neck pain and a slight effect on shoulder pain in the intervention group. Various forms of therapeutic exercises have been used in the secondary prevention of low back and neck pain and shown consistent moderate effect to prevent symptoms from becoming chronic (12).

Summary and implications for further research Lifestyle factors, e.g. overweight/obesity and smoking are risk factors for LBP and some other musculoskeletal disorders. The independent effects are typically moderate ; however the joint effects of different lifestyle factors and the joint effects of lifestyle factors and environmental factors are largely unknown (13). Future studies should address these questions when large representative population samples are available. The metabolic and hormonal background of men and women differ ; therefore gender specific analyses are recommended. Although few intervention studies have been targeted at lifestyle factors with an MSD as a primary outcome, available evidence from observational studies suggests that health promotion should be considered both in primary and secondary prevention of MSDs.

References
1. Shiri R, Karppinen J, Leino-Arjas P, Solovieva S, Viikari-Juntura E. The Association Between Obesity and Low Back Pain : A Meta-Analysis. Am J Epidemiol. 2010 Jan 15 ; 171(2):135–54. Epub 2009 Dec 11.
2. Snijder MB, van Dam RM, Visser M, et al. What aspects of body fat are particularly hazardous and how do we measure them ? Int J Epidemiol 2006 ;35:83–92.
3. Shiri R, Karppinen J, Leino-Arjas P, Solovieva S, Viikari-Juntura E. The Association Between Smoking and Low Back Pain : A Meta-Analysis. Am J Med. 2010 Jan ; 123(1):87.e7-35.
4. Hildebrandt VH, Bongers PM, Dul J, van Dijk FJ, Kemper HC. The relationship between leisure time, physical activities and musculoskeletal symptoms and disability in worker populations. Int Arch Occup Environ Health. 2000 Nov ;73(8):507-18.
5. Hamberg-van Reenen HH, Ariëns GA, Blatter BM, van Mechelen W, Bongers PM.A systematic review of the relation between physical capacity and future low back and neck/shoulder pain. Pain. 2007 Jul ;130(1-2):93-107. Epub 2007 Jan 11.
6. Chen SM, Liu MF, Cook J, Bass S, Lo SK. Sedentary lifestyle as a risk factor for low back pain : a systematic review. Int Arch Occup Environ Health. 2009 Jul ;82(7):797-806. Epub 2009 Mar 20.
7. Shiri R, Karppinen J, Leino-Arjas P, Solovieva S, Varonen H, Kalso E, Ukkola O, Viikari-Juntura E. Cardiovascular and lifestyle risk factors in lumbar radicular pain or clinically defined sciatica : a systematic review. Eur Spine J. 2007 Dec ;16(12):2043-54. Epub 2007 May 25.
8. Pietiläinen KH, Kaprio J, Borg P, Plasqui G, Yki-Järvinen H, Kujala UM, et al. Physical inactivity and obesity : a vicious circle. Obesity (Silver Spring) 2008 ;16(2):409-14.
9. Leino-Arjas P, Kauppila L, Kaila-Kangas L, Shiri R, Heistaro S, Heliövaara M. Serum lipids in relation to sciatica among Finns. Atherosclerosis. 2008 Mar ;197(1):43-9. Epub 2007 Sep 7.
10. Shiri R, Viikari-Juntura E, Leino-Arjas P, Vehmas T, Varonen H, Moilanen L, Karppinen J, Heliövaara M. The association between carotid intima-media thickness and sciatica. Semin Arthritis Rheum. 2007 Dec ;37(3):174-81. Epub 2007 May 15.
11. Mattila R, Malmivaara A, Kastarinen M, Kivelä SL, Nissinen A. The effects of lifestyle intervention for hypertension on low back pain : a randomized controlled trial. Spine 2007 Dec 15 ;32(26):2943-7.
12. Linton SJ, van Tulder MW. Preventive interventions for back and neck pain problems : what is the evidence ? Spine. 2001 Apr 1 ;26(7):778-87..
13. Schulte PA, Wagner GR, Ostry A, Blanciforti LA, Cutlip RG, Krajnak KM, Luster M, Munson AE, O’Callaghan JP, Parks CG, Simeonova PP, Miller DB. Work, obesity, and occupational safety and health. Am J Public Health. 2007 Mar ;97(3):428-36. Epub 2007 Jan 31.