A total of 13
695 factory workers or spouses were interviewed, and 4649 (34%) had rural relatives. Of these, 4277 (92%) factory workers or spouses agreed to participate in the clinic together with their rural relative. By the end of the study period, 2111 (49%) rural participants had attended the clinics, with a median time from invitation to clinic participation of 87 days (range 1–963). Sixty one were excluded from analyses because they reported their place of residence as urban, and a further 67 were excluded because they fell outside the age range of 20–69 years, leaving 1983 rural participants (1375 men and 608 women) for the present analyses. Data were complete for all the variables except physical activity (16 missing), and biochemical assays (six missing).
Table 1 shows the characteristics of the study population. The participants’ median ages were 40 and 42 years for men and women respectively. The 1983 participants came from 18 of India’s 28 states (roughly 1600 villages), and 1765 (89%) came from the four large states in which the factories were located, reflecting the migration patterns of workers and their spouses in these factories. The median travel time to the study centre was 6 hours (range 0–52), with a quarter of the participants travelling for over 12 hours (roughly 600 km in distance). The median travel time was 8 hours (interquartile range 4–13) for the participants in north India and 5 hours (3–9) for those in south India.
Table 1 Characteristics of the rural participants of the Indian Migration Study. Values numbers (percentages) of participants
Table 2 shows the distribution of risk factors by age categories. The prevalence of most of the risk factors was higher in older age groups, although for some risk factors it seemed to decline in the oldest age group, possibly due to the small number of participants. Table 3 shows the age standardised prevalence of risk factors by socioeconomic position and sex. Tobacco and alcohol use, low fruit and vegetable intake, and underweight and short stature were more common in the lower socioeconomic groups. Obesity was more prevalent in the higher socioeconomic groups, as were dyslipidaemia and diabetes (in men only) and hypertension (in women only). Tobacco and alcohol use was more common in men, while obesity and low intake of fruit and vegetables was more prevalent in women. The age standardised prevalence of either form of tobacco use (smoked or chewed) was 39.8% (95% confidence interval 37.2% to 42.4%; n=543) in men and 4.4% (2.8% to 5.9%; n=27) in women (P<0.001).
Table 2 Distribution of risk factors for non-communicable diseases in rural participants of the Indian Migration Study by age and sex. Values are percentages (95% confidence intervals) unless stated otherwise
Table 3 Age standardised prevalence of risk factors for non-communicable diseases in rural participants of the Indian Migration Study by socioeconomic position. Values are percentages (95% confidence intervals) unless stated otherwise
The prevalence of self reported medical conditions was low: 1.1% (n=15) and 1.8% (n=11) of men and women respectively reported heart disease, 5.1% (n=70) and 11.5% (n=70) reported high blood pressure, 3.4% (n=46) and 4.3% (n=26) reported diabetes, and 0.4% (n=5) and 0.8% (n=5) reported stroke. To investigate whether the low prevalence of risk factors was attributable to social patterning of access to medical care, we examined the prevalence of self reported and newly diagnosed hypertension by the socioeconomic groups. There were clear social trends in the prevalence of self reported hypertension (3.6% (n=9) in low socioeconomic group, 5.5% (n=28) in medium group, and 8.6% (n=105) in high group; Ptrend=0.001) but not in the prevalence of newly diagnosed hypertension (14.3% (n=36), 12.1% (n=60), and 14.4% (n=173) in low, medium, and high groups; Ptrend=0.6). When examined separately by sex, the prevalence of self reported hypertension by socioeconomic group was 5.8% (n=6), 13.6% (n=20), and 12.9% (n=46) in low, medium, and high groups in women (Ptrend=0.1); and 2.2% (n=3), 2.3% (n=8), and 6.8% (n=59) in the three groups in men (Ptrend<0.001).
The figure shows the prevalence of risk factors standardised to the distribution of age and socioeconomic conditions of the general rural population of India (from the National Family Health Survey35
). The standardisation adjusted the prevalence of risk factors downwards (if the risk factor was more common in upper socioeconomic groups) or upwards (if the risk factor was more prevalent in the lower socioeconomic groups), suggesting that our population was relatively more affluent. The overall patterning of risk factors, however, was largely unchanged: tobacco and alcohol use were more common in men, while obesity was more prevalent in women. Although dyslipidaemia (total:HDL cholesterol ratio ≥4.5) was equally prevalent between men and women, women had higher prevalence of both high total cholesterol (levels ≥5.18 mmol/l: 21.1% (n=289) men v
27.8% (n=167) women; P=0.01) and low HDL cholesterol (31.2% (n=428) men with HDL cholesterol ≤1.03 mmol/l v
65.7% (n=398) women with HDL cholesterol ≤1.28 mmol/l; P<0.001). Apart from underweight, risk factors were generally more prevalent in south Indians compared with north Indians (see web tables 1 and 2 on bmj.com).
Standardised prevalence of risk factors for non-communicable diseases in rural participants of the Indian Migration Study. (See table 3 for definitions of risk factors)