Our analysis indicates that in the working populations studied, multisite musculoskeletal pain was substantially more common in the UK than in India. However, among workers in the UK of Indian sub-continental origin, including first generation migrants and those aged < 35 years, rates of pain were close to those of their white colleagues. These results suggest that whatever drives the much higher prevalence of musculoskeletal pain in the UK than India is environmental rather than genetic, affects multiple anatomical sites, begins to act by early in adult life, and has impact fairly soon after people move from India to the UK.
Our study benefited from a high response rate among those eligible to take part. Moreover occupational exposure to physical activities was (by design) much the same among the three groups of manual workers, and rather lower among the three groups of non-manual workers [5]. Differences in the physical demands of work are therefore unlikely to explain the lower prevalence of pain in Indian manual workers.
It is possible that some workers with disabling musculoskeletal pain were excluded from the sampling frame because they were absent from work at the time of the survey or had been forced to leave their jobs, and that this healthy worker selection was stronger in India than in the UK. However, we think it is unlikely that any resultant bias could explain such large differences in pain prevalence as were observed. For that to occur, well over half of all men taken on to work in the Indian manual jobs would have to leave their jobs because of musculoskeletal pain.
An earlier report, based on the same study, described the prevalence of pain in the past month at specific anatomical sites [5]. However, in the current analysis, we focused on the one-year prevalence of symptoms since it was expected to provide a more sensitive measure of general propensity to pain, and for that reason had been used previously in the CUPID study [3, 4]. For this purpose it did not matter whether the pain at different anatomical sites had occurred simultaneously – only the number of sites that had been affected at some time during the period of interest. Recall of pain over the longer period may not have been as accurate as that for the past month. However, we know from the earlier analysis that in comparison with participants in the UK, the Indian workers, and especially those in manual jobs, also had a lower one-month prevalence of pain in both the low back and arm [5]. It therefore seems unlikely that the differences we observed in the one-year prevalence of multisite pain can be attributed to errors in recall.
Ideally, as in the CUPID study, our assessment of the extent of pain would have distinguished between upper limb pain affecting the right and left sides of the body. However, the questionnaire that had been used when interviewing workers in India had not asked about the laterality of pain in the elbow and wrist/hand, and therefore it could not be done.
Another possible source of bias was differences in understanding of the term, pain, especially when the questionnaire was translated into Marathi. However, among the Indian manual workers, the prevalence of pain was much the same, whether interviews were in Marathi or English (data available on request).
In the logistic regression analyses for Table 3, we took UK white, non-manual workers as our reference since they provided reasonable representation across the distribution of covariates. However, we did also make direct pairwise comparisons between other groups of workers. Importantly, the risk of pain at ≥3 sites among Indian manual workers was significantly lower, not only than that in the main reference group, but also than that in UK manual and non-manual workers of Indian subcontinental origin. The subsidiary analyses for younger workers and those who were first generation migrants to the UK included fewer participants, and were therefore subject to greater statistical uncertainty. Nevertheless, again with pain at ≥3 sites as the outcome, the risk for Indinan manual workers was significantly lower than that in UK manual and non-manual workers who were first generation migrants from the Indian subcontinent. And among participants aged < 35 years, risk among Indian manual workers was significantly lower than for UK manual and non-manual workers of Indian subcontinental origin.
The levels of pain prevalence that we found in our study cannot be compared directly with those in other surveys that have been based in the general population rather than workers in employment, covered different age ranges, and used different outcome measures (e.g. chronic widespread pain). However, our finding that rates of pain were lower in India than in the UK is consistent with the CUPID study, in which prevalence was lower in Pakistan and Sri Lanka than in the UK [2,3,4]. Moreover, as in the CUPID investigation, the differences applied to musculoskeletal pain in general and were not limited to just one or two anatomical sites. It is striking, however, that rates of pain among UK workers of Indian subcontinental origin were close to those of their white colleagues. Furthermore, this appeared to apply also to the subset of first generation migrants, and when analysis was restricted to younger ages (< 35 years).
We have been unable to identify any other studies that used standardised methods to compare the prevalence of musculoskeletal pain in migrant populations with those both in their country or region of origin and in the country to which they had moved. However, a survey in the North-West of England found that pain in the past month lasting > 1 week was slightly more common among migrants from South Asia than in the local white population, while “pain in most joints” lasting > 1 week in the past month was substantially more frequent [8]. A second study, which recruited also in the West Midlands, similarly found a higher prevalence of widespread pain (“all over the body in the past month”) in South Asian ethnic groups than in white Europeans [9]. And in a more recent survey carried out in the Tower Hamlets district of London, the prevalence of chronic widespread pain (in two contralateral quadrants of the body and also the axial skeleton and present for at least three months) was greater among people of Bangladeshi origin than in white British/Irish participants [10]. While these investigations differed from ours in the pain outcomes that were examined and the demographics of the populations studied, they support the view that rates of pain in South Asian migrants to the UK are at least as high as in the indigenous white population.
The pattern of results in our study implies that the drivers of the large differences in musculoskeletal pain between workers in India and the UK are environmental, and predispose to pain at multiple anatomical sites. It suggests, moreover, that they act early in the lifecourse, and begin to affect migrants fairly soon after they move from India to the UK. Beyond this, our data do not indicate what the drivers might be, but one possibility is that awareness of musculoskeletal pain and responses to it are importantly influenced by a person’s social environment, in the same way that a number of other illnesses appear to be culturally determined [11]. If so, rates of musculoskeletal pain would be expected to decline when people migrate from countries with high prevalence (e.g. in South and Central America) to places where it is less frequent (e.g. in Europe) – a hypothesis that would be worth testing in future research.
