The prevalence and correlates of low back pain in adults : A cross sectional study from Southern India

Low back pain is a major public health problem all over the world. It is generally assumed that overweight, height and low back pain are related. However, the scientifi c evidence to support this relationship is not fully conclusive. The aim of this study is to estimate the prevalence of low back pain and its association with height, fat distribution, reproductive history and socioeconomic infl uence. A representative sample of 401 men and 403 women aged 20 years and above were selected and studied. It is found that 28.4% and 52.9% respectively were having low back pain. Height and fat distribution were found to have no association with low back pain. Both men and women, whose household were in the lower socio economic status reported more back pain (Adjusted odds ratio (AOR) for men 1.61, 95% confi dence interval (CI): 1.02, 2.55 and AOR for women 1.57, 95% CI: 1.02, 2.34). Men with lower educational qualifi cation reported more back pain (AOR 1.89, 95% CI: 1.08, 3.31). In women, those who have undergone caesarean section (AOR 1.661, 95% CI: 1.02, 2.72) and sterilization (AOR 1.63, 95% CI: 1.09, 2.44) were found to be a positively associated with low back pain. The only socioeconomic link with back pain among women seemed to be manual occupation (AOR 3.33, 95% CI: 1.49, 7.4). The fi nding confi rms the higher burden of back pain on the socially disadvantaged, but cannot yet be explained by known risk factors.


INTRODUCTION
Low back pain is an emerging public health problem all over the world.It is generally assumed that overweight and low back pain are related [1] .However, scientifi c evidence to support this relationship is not fully conclusive. [2,3,4]Some studies have reported that subjects who carry excessive abdominal fat mass over a long period may be at risk of low back pain, as a result of altered posture to counter balance the protruding fat mass. [5]It is also observed that height may relate independently to low back pain from large abdominal fat mass and may aggravate back pain associated with stooping especially in those with large waist or large abdominal fat mass. [5]These people may require more reactive forces to counteract the gravitational pull on this fat mass to achieve balance, especially when bending forward for lifting or when walking downstairs.As a result, more strain may be exerted on their lower back.Some studies have proved that those with central fat distribution, indicated by high waist to hip ratio, which may be at increased risk of low back pain independently from total fatness, measured by body mass index.However, other evidence of low back pain and height is confl icting.Studies were reported that there was no association between height and low back pain even after age and lifestyle adjustments. [5,6]But, Heliovaara, 1987 reported that men above 180 cm and women above 170 cm had 2 and 4 times risk of herniated lumber intervertebral disc compared to those who were 10 cm shorter. [7]On the other hand Kelsey 1975 found no association between height and low back pain. [8]nternational Journal of Medicine and Public Health | Oct-Dec 2013 | Vol 3 | Issue 4 lifting of heavyweights. [10].There is some evidence linking backache with behaviors that differ across social groupings such as cigarette smoking [11] and stress and psychiatric morbidity. [12]Although the evidence relating to such risks is far from consistent, [8] it provides the basis for interpreting socio-economic differences in back pain occurrence.However, these earlier studies on the association of low back pain and socio-economic infl uences among women have not considered type of delivery, sterilization and other reproductive history which may confound the results.
In India, nearly 60 percent of the people have signifi cant back pain at some time or the other in their life. [13]However, most of the earlier studies in India were hospital based and rarely the population based studies were done on the association of low back pain with socioeconomic class and other anthropometric measures.The present study, is aimed at fi nding the prevalence of low back pain and to examine its association with height, fat distribution, reproductive history and socio-economic infl uences.

Sample size estimation and sampling methods
Assuming the prevalence of low back pain as 60% with an allowable error of 5%, the minimum sample size required for this study was calculated to be 800.The sample was selected in two stages.The study was conducted in the non-slum areas of the fi eld practice area of the Urban Health Centre of PSG Institute of Medical Sciences and Research, Coimbatore.The primary sampling unit (PSU) was selected randomly from the list of such areas.In the second stage, the households were selected using simple random sampling within each selected PSU.According to the National Family Health Survey data of India, about 56% of the population belongs to the age group of 20 years and above. [14]Based on these values, the expected number of subjects was estimated to be 14384, in 4348 households.In order to get 800 subjects, 300 households were required to be selected.Using random numbers, four non-slum areas from 12 non-slum areas were selected.The required number of households were selected proportionately from the four non-slum areas to make the design self weighting.Of the 300 households selected, seven houses were found locked, even after the third visit.In such a case, as replacement, neighboring houses were selected.Thus, a total of 804 subjects were interviewed from 307 households.The Institutional Human Ethics committee of the institution approved all subject recruitments and data collection procedures.The data collection was done from June 20 to July 20, 2011.

Data collection methods
A brief questionnaire was used to screen, among the respondents, the occurrence of low back pain in the past year.The questions included occurrence of low back pain, demographic factors and reproductive health history.Low back pain was identifi ed among subjects who have back pain lasting for more than a day in an area between the lower costal margin and the gluteal folds with or without radiation into leg to below the knees during the past one year [5] .Episodic and persistent types of pains were included.However; pregnant women were excluded and subjects who were not able to communicate because of dialect or hearing problems were also excluded.
The anthropometric measurements included measures of body height (cm) and weight (kg) using standard measurement equipments, which were performed in an empty room with the subjects wearing light indoor clothing and no shoes.Few investigators were trained in taking anthropometric measurements and performed in each day.Standing height was measured using non stretchable tape suspended from the wall and was measured to the nearest 0.1 cm.Weight (kg) was measured to the nearest 0.5 Kg.Waist and Hip circumference (cm) were assessed using a measuring tape while the subject was standing.Other factors examined were occupation, education and smoking.In women current menstrual status, multiparity, type of delivery, sterilization and use of oral contraceptives were also examined.[17][18][19] Sociodemographic background included age (in years), highest education level attained (upto higher secondary vs University level education), Occupation (Manual laborers vs. Non-manual laborers), number of family members and monthly income.Age was self reported and defi ned as the age at time of examination.Women were asked about multi-parity (<2 vs ≥2), type of delivery (Caesarean vs others), current menstruation (No vs Yes), Sterilization (No vs Yes), and also the use of oral contraceptives (No vs Yes).

Statistical analysis
The Socio Economic Status (SES) was measured based on Prasad's modifi ed classifi cation.This was based on consumer price index (Industrial workers) (CPI (IW)) for the month of May 2011 after rounding off to the nearest Rs. 10.Those with per capita monthly Income of Rs. 4270 and above were classifi ed as class I. [20] Body Mass Index (BMI) was computed for male and female using the formula weight (kg)/ height (m 2 ).Subjects were classifi ed as overweight if their BMI was equal to or greater than 25 Kg/m 2 .The waist circumference was divided into two groups: <80 cm and ≥80 cm for women and <90 cm and ≥90 cm for men [21] .The ratio of waist to hip circumference was calculated and the data was divided into two groups: <0.8 and ≥0.8 for women and <1.00 and ≥ 1.00 for men. [21]Analysis was done for men and women separately.Continuous variables, such as height and weight were divided into percentiles.The prevalence of low back pain in various age groups of 10 year width was analyzed using descriptive statistics (mean and median for continuous variables and percentages for categorical variables).Z-test was used to compare the prevalence in men and women.The relationship between the prevalence of low back pain and anthropometric parameters was evaluated with logistic regression (unadjusted odds ratio and 95% CI).For analyzing the association of reproductive history with low back pain, age adjusted odds ratio and 95% CI were reported.Sequential logistic regression model, were used to assess the association between the socioeconomic infl uences and low back pain controlling other risk factors.All the analysis was done using the Statistical package for social sciences (SPSS), version 11.5

RESULTS
Among 401 men studied, 28.4% were having low back pain and among 403 women studied, 52.9% were having low back pain.Table 1 highlights that the prevalence of low back pain (LBP) was highest (50%) in the age group (41-50 years) compared to other age groups.In younger age group.(20-30 years) the prevalence was found to be 30.8%.In general the prevalence of LBP was higher in women (52.9%) compared to men (28.4%) and the difference was statistically signifi cant (P < 0.001).
The median height was 165 cm for men and 153 cm for women respectively.The median weight was 64 Kg for men and 60 Kg for women respectively.Tall stature (for men OR = 0.84; for women OR = 0.72), waist circumference (for men OR = 1.26; for women OR = 1.07), waist hip ratio (for men OR = 1.91; for women OR = 0.85), and Body Mass Index (for men OR = 1.31; for women OR = 1.11) were found to have no association (P > 0.05) with low back pain in both men and women.This has been illustrated in Table 2. Also smoking in men had no signifi cant relationship with low back pain.All the women studied were non-smokers.
Table 3 shows the association of low back pain with reproductive history.Women who have undergone Caesarean section were found to have a positive association with low back pain (adjusted odds ratio 1.661, 95% CI: 1.02, 2.72).Also sterilization was found to be a risk factor of low back pain (adjusted odds ratio 1.63, 95% CI: 1.09, 2.44).Parity, post-menstruation and use of oral contraceptives had no signifi cant relationship with low back pain.Table 4 shows that both men and women whose households were in the lower socio economic status reported more back pain than those in the higher socio-economic status (adjusted odds ratio for men 1.61, 95% CI: 1.021, 2.55 and adjusted odds ratio for women 1.57, 95% CI: 1.02, 2.34).These associations were not explained by smoking and obesity.Men with lower educational qualifi cation reported more back pain than those with university and higher education qualifi cation (Adjusted odds ratio 1.89, 95%

DISCUSSION
This study, conducted in the urban fi eld practice area of PSG Institute of Medical Sciences and Research, Coimbatore, provided the data on the prevalence of self reported low back pain.This study showed a high prevalence of low back pain (40.7%) in subjects aged 20 years and above.The prevalence was signifi cantly higher among women (52.9%) compared with men (28.4%) and the difference was statistically signifi cant (P < 0.001).In other words, one out of the three people in the fi eld practice area had at least one day low back pain in the past one year.With such prevalence there is a high demand for health education and service provision focused on these populations.A recent study among Danish twins reported similar high prevalence of LBP. [22]In another study found that LBP at age 18 signifi cantly increased the risk of LBP at age 30. [23]This present study showed a prevalence of 30.8% in the age group (20-30years).This indicates that it is important to learn more about this condition in the younger age in order to implement primary preventive measures at an early age.
In this study, no association was found between height and low back pain.There are several studies that conform to the pattern that height is not correlated with the occurrence of low back pain in women, though in men many studies reported a positive correlation [15,17,18] .This study has also examined the association between low back pain and weight.The results conform to the pattern wherein weight does not correlate with the occurrence of low back pain and is consistent with previous studies. [24]These fi ndings provide no evidence that a greater body mass index and waist-hip ratio is associated with an increased risk of low back pain.These results support the fi ndings of YP Yip [24] and contrast with fi ndings of Han et al., [5] In this study, women who have undergone caesarean section or sterilization reported more low back pain than who have not undergone these procedures.This may be due to the sedentary life style after the caesarean section.Nevertheless, it was also observed that women who have occupation described as "Physically demanding" also have higher risk of low back pain suggesting that extremes of activity are probably not ideal.
In this study, socio-economic status was inversely associated with low back pain in men.The rationale for examining socio economic infl uences on common symptoms is that any differences in social group may be the effect of preventable environment or lifestyle risks.For example, measures of social class based on income may refl ect alcoholism, smoking habits, obesity or occupations which have an effect on back pain. [9]A number of epidemiological studies have reported a link between smoking and back pain which shows a 'doseresponse' relationship. [9]Biologically plausible explanations of the association between smoking and back pain, particularly those related to the effect of smoking on nutrition of the disc have been reviewed by Ernst. [9]However; in this study we could not observe a signifi cant association between smoking and obesity with low back pain.
In women, even after adjusting age, body mass index, type of delivery and sterilization, the association between lower socio economic status and low back pain was statistically signifi cant.This study supports the fi ndings of Hagen KB. [25][26][27] The conclusion is that in this population socio-economic difference in reporting back pain cannot be explained by age, height, weight, body mass type of delivery and sterilization.The strongest association with reported back pain in women among the various measures which we examined was occupation.In general, women doing manual labor reported more back pain.The women of low socio economic status, because of their increased economic demand, may not take adequate rest during episode of back pain leading to inadequate healing and recurrence of back pain, which may be specifi c to Indian population.The increased reporting in back pain patterns by manual women workers compared with non-manual women workers suggests that the infl uence of manual work in the adult female population is stronger than the risk of sedentary work.
This study has several limitations.First, since the defi nition of low back pain is inconsistent, one should limit the comparison to the previous studies using a similar defi nition of low back pain.Second, the study population constituted of people living in fi eld practice area of our health centre.For this reason, our fi ndings may not be generalized to other socio-economic strata.In the main analysis, physical activity and use of Copper-T were not included which may confound the results.Third, the association of psychological factors on prevalence of low back pain was not elicited.Finally, the study design was cross sectional and a further prospective study is wanted to investigate the risk factors of low back pain in women and men.Despite these limitations, this study has several strengths.Systematic ways of data collection by the same investigators avoided inter observer variations.There are not many population studies conducted in India in this area.Additionally data on demographic background, reproductive history and anthropometric measurements collected allowed us to examine the associations between socio economic infl uences on low back pain.In conclusion, it seems clear that the poorer and more socially disadvantaged groups have a proportionally higher burden of this disabling symptom than the better off in society.While the etiological importance of these remains uncertain, back pain affords a clear example of the unequal experience of the socio economic status in the society.This leads to the need to search more variables like consumption of micro nutrients in the diet that are more commonly associated with low socio economic status.

Table 2 : Association of self-reported Low Back Pain with anthropometric measures and smoking
: 1.08, 3.31).Similar association was not observed among women.In women, the only socio-economic link with back pain seemed to be manual occupation (Adjusted odds ratio 3.33, 95% CI: 1.49, 7.40). CI

Table 4 : Association of self reported Low Back Pain with socio-economic measures
Odds ratio adjusted for age, smoking and body mass index in men and adjusted for age, body mass index, type of delivery and sterilization in women.LBP refers to low back pain.**P < 0.05