The main findings of this study among newly educated health care workers without prior history of LBP were that overweight and obese female health care workers were not at increased risk for LBP two years after graduation. On the other hand, female health care workers with high physical work demands were at increased risk for LBP. As our study was conducted on respondents without prior history of LBP, the results support the notion that BMI and LBP are not causally related, thereby lending credence to previous studies not finding an association between BMI and LBP [21
Our study is the first to investigate the effect of overweight and obesity on the development on LBP among newly educated female health care workers without prior history of LBP. However, another study by Van Nieuwenhuyse et al. look into the effects of physical characteristics measured in physical examinations on the development of LBP among health care workers and distribution companies with no or little LBP history [24
]. That study finds a significant effect of obesity on later development of LBP among asymptomatic health care workers. However, their results are not directly comparable to ours because their analysis did not control for work environment factors. Although overweight and obesity do not seem to be risk factors for developing LBP among health care workers, they were shown to be related with the development of hypertension, coronary heart disease, type 2 diabetes and stroke [25
]. Notably, 41% of female health care workers were overweight in our study population. Thus, from a public health perspective, initiatives for reducing overweight and obesity among health care workers are recommended.
Female health care workers with high physical work load had 78% increased risk for developing LBP compared to their colleagues with low physical work load. This finding validates previous observations among health care workers [11
], although neither of these included newly educated female workers without prior history of pain. Our unique design provides strong evidence that high physical work load increases the risk for the development of LBP among health care workers. The strength of our study is the baseline population without prior exposure to health care work and without a life-time history of LBP, followed prospectively for two years into their working life after graduation. This is particularly important given that a previous study has indicated that LBP and disability due to LBP during baseline is a significant indicator for dropout in the following two years [9
]. As shown in Table , there was no difference among respondents with normal weight, overweight and obese concerning their estimated physical workload. As many respondents may have been overweight or obese for several years, a concern is the selection of overweight and obese individuals without LBP in the analysis. An additional analysis showed no differences in prevalence of LBP between normal weight (60%) and overweight (58%) respondents at baseline, whereas obese showed a significantly increased prevalence of LBP (65%, P
0.001). However, the cross-sectional nature of this baseline correlation does not reveal anything about causality. Because previous episodes of LBP have been shown to be a risk factor for new episodes of LBP [14
], the exclusion of respondents with prior history of LBP strengthens the validity of our findings. Self-administered questionnaires have been criticized for not providing accurate information on exposure to physical work load. However, persons with LBP may tend to perceive their physical workload as higher than those without LBP [28
], bringing the results that include those with previous LBP to question [11
]. As the respondents included in our study had no prior history of LBP, a systematic bias on the reported physical work load is not very likely.
Recall bias is a limitation of questionnaire research. Thus, some people may have forgotten a previous experience of LBP. Because the mean age of the newly educated health care workers was 35
years, many may have had experience working in other jobs and have forgotten periods of LBP. Thus, we controlled for age in the analyses. Finally, other factors like job satisfaction and education that have not been included in our analyses could be confounders in the relationship between physical work load and BMI and LBP.