Relationship of anthropometric indicators with blood pressure levels in rural Wardha
Deshmukh, P R
Background & objectives: Overweight and obesity are important determinants of health leading to adverse metabolic changes, including increase in blood pressure. Being overweight is associated with two- to six-fold increase in the risk of developing hypertension. Studies in urban Indian population showed strong relationship between different anthropometric indicators and blood pressure levels. Surprisingly, little is known about these relationships in rural population of India. The present study was carried out to examine the relationship between different anthropometric indicators and blood pressure levels in rural population of Wardha district in central India.
Methods: This cross-sectional study was carried out in the areas of two Rural Health Training Centres (RHTC) of Department of Community Medicine, Mahatma Gandhi Institute of Medical Sciences, Sewagram; namely Bhidi and Anji through house-to-house visits. Two stage sampling method (30 cluster followed by systematic random) was used to reach the respondents’ households. Partial correlation coefficients were used for continuous variables. Linear regression analysis was used to assess the influence of different anthropometric indicators on the systolic and diastolic blood pressure. ROC analysis was done to identify optimal cut-off values while likelihood ratios were calculated to identify the odds of having hypertension in comparison to those with lower values of anthropometric indicators.
Results: The mean systolic blood pressures were 120.2 and 118.4 nimHg while the mean diastolic blood pressures were 77.7 and 76.3 mmHg in men and women respectively. There was a significant positive correlation of obesity indicators with both systolic and diastolic blood pressure. For SBP, the correlation coefficient was 0.23 with BMI, 0.23 with waist circumference, 0.11 with WHR and 0.22 with WHtR. For DBP, it was 0.13 with BMI, 0.12 with WC, 0.04 with WHR and 0.11 with WHtR. Step-wise linear regression suggested that BMI and WC were important predictors of hypertension. The suggested cut-off values for BMI were 21.7 for men and 21.2 for women; for waist circumference, the cut-offs were 72.5 for men ami 65.5 for women.
Interpretation & conclusion: BMI and WC had strong correlation with systolic and diastolic blood pressure. The suggested lower cut-off values of the anthropometric indicators will cover maximum of the population with higher odds of having hypertension and may help in reducing the mean population blood pressure levels.
Key words Body mass index – hypertension – likelihood ratio – obesity – ROC – waist circumference – waist-height ratio – waist -hip ratio
Overweight and obesity are important determinants of health and lead to adverse metabolic changes, including increase in blood pressure, unfavourable cholesterol levels, hypertriglyceridaemia, increased resistance to insulin, low high density lipoprotein (HDL) and greater prevalence of metabolic syndrome1. They raise the risk of coronary heart disease, stroke, type 2 diabetes mellitus and many forms of cancer. The prevalence of obesity is increasing in both developed and developing countries2.
Body mass index or BMI (weight in kilograms divided by the square of the height in meters) is promulgated by the World Health Organization as the most useful epidemiological measure of obesity. It is nevertheless a crude index that does not take into account the distribution of body fat, resulting in variability in different individuals and populations2. Waist-hip circumference ratio (WHR), waist-height ratio (WHtR) and waist circumference are commonly used to predict the risk of obesity related morbidity and mortality as they account for regional abdominal adiposity3-5.
Being overweight is associated with two- to six-fold increase in the risk of developing hypertension. An increase of 2-3 mmHg in systolic and 1-3 mmHg in diastolic blood pressure has been shown for each 10 kg increase in weight in western population6. Studies in urban Indian population also showed strong relationship between different anthropometric indicators and blood pressure levels7-9. Little is known about these relationships in rural Indian population. The present study was therefore undertaken to examine the relationship between different anthropometric indicators and blood pressure levels. in rural population of Wardha district in central India.
Material & Methods
Study design & setting: This cross-sectional study was carried out in the areas of two Rural Health Training Centres (RHTC) of Department of Community Medicine, Mahatma Gandhi Institute of Medical Sciences, Sewagram; namely Bhidi and Anji through house-to-house visits during May-June 2004.
Sampling design: Two stage sampling method was used to reach the respondents’ households. In first stage, cluster sampling method10 was used to identify 30 clusters in each RHTC area separately (Sampling interval was 644 for RHTC, Bhidi and 1383 for RHTC, Anji). In the second stage, systematic random sampling method was used to identify 16 households per cluster in RHTC, Bhidi area and 32 households per cluster in RHTC, Anji area. As the population of RHTC, Anji area was almost double the population of RHTC, Bhidi area, we doubled the respondents from each cluster of RHTC, Anji area to get better representation from all the clusters. All households in the cluster were listed and number of households was divided by the required number of households (16 in Bhidi and 32 in Anji) to get the sampling interval. First household was selected randomly by using lottery method and then subsequent households were identified by adding sampling interval to the random number.
All family members of 18 yr and above from the selected households were included in the study. The teams visited the households in morning and evening time only to get maximum number of family members at home. Two visits were made to ensure maximum participation in the study. The objective of the study and the method was explained to the formal and informal leaders of the clusters and eligible people were requested to stay at home on the scheduled date and time. Those who were absent were asked to be present at the second visit. Pregnant women and those who were unable to stand erect were excluded from the study.
Measurement of blood pressure: After obtaining oral consent, blood pressure was measured on left arm by auscultatory method using mercury sphygmomanometer (Diamond Co., Industrial Electronics and Allied Products, Electronics Cooperative Estate, Pune, Maharashtra). The individual was made comfortable and seated at least for five minutes in the chair before measurement. Two readings were taken half an hour apart and the average of two was taken11. Hypertension was defined as systolic blood pressure (SBP) >140 mmHg and/or diastolic blood pressure (DBP) >90 mmHg as per US Seventh Joint National Committee on Detection, Evaluation and Treatment of Hypertension (JNC VII) criteria12.
Anthropometrical measurement: Body weight was measured (to the nearest 0.5 kg) with the subject standing motionless on the bathroom weighing scale13. Each weighing scale was standardized every day with a weight of 50 kg. Height was measured (to the nearest 0.5 cm) with the subject standing in an erect position against a vertical scale of portable stadiometer and with the head positioned so that the top of the external auditory meatus was in level with the inferior margin of the bony orbit. BMI was calculated as weight in kilograms divided by squared height in meter. Waist circumference was measured at the level halfway between the iliac Crest and the costal margin in the mid-axillary line after exhaling with the subject in standing position. Hip circumference was measured at the level of greater trochanters with the subject in standing position and both feet together. Two consecutive recordings were made for each site to the nearest 0.5 cm using a non stretchable fibre measuring tape on a horizontal plane without compression of skin. The mean of two sets of values was used11.
BMI >23.0 and >25.0 kg/m^sup 2^ was taken as cut-off for overweight and obesity respectively. Waist circumference (WC) cut-offs were taken as >90 for males and >80 for females, to define overweight14. The cut-off used for WHR were >0.9 for males and >0.8 for females15. For WHtR, the cut-off used was 0.5 for both sexes16.
Data analysis: Data were analyzed using SPSS 10.0. The population characteristics, anthropometriC indicators, SBP and DBP are shown as mean and standard deviation. Standard error was analyzed by CSample program of epi_info 6.04 software as the data were collected by cluster sampling method. Means were compared by using t-test Partial correlation coefficients were used for continuous variables. Linear regression analysis was used to assess the influence of different anthropometriC indicators on the SBP and DBP. Receiver operating characteristics (ROC) analysis was done to identify the cut-off values of anthropometric indicators to identify the risk of hypertension. Sensitivity and specificity were calculated and point having highest sum was taken as cut-off value for the indicator. Software CIcalculator was used to calculate 95 per cent confidence interval (CI) of the sensitivity and specificity17. Likelihood ratio (LR) was calculated as sensitivity/ (1-specificity) to estimate the odds of having hypertension in subjects with various cut-off values of the anthropometric indicators in comparison to those who have lower values of anthropometric indicators. All tests of significance were two tailed and level of significance was taken at P
Results
Of the total 3514 individuals above 18 yr of age in the study area, 2746 individuals were included giving the coverage of 78.15 per cent. Of these, 46 records were incomplete and hence here we present the analysis of 2700 individuals.
The mean systolic blood pressures were 120.2±0.54 and 118.4±0.51 mmHg and mean diastolic blood pressures were 77.7±0.38 and 76.3±0.61 mmHg in men and women respectively (Table I). The prevalence of the hypertension was 21.8 per cent among males and 19.8 per cent among females.
The prevalence of overweight and obesity defined as BMI >23.0 and >25.0 was found to be 6.5 and 5.1 per cent in males respectively and 5.4 and 5.2 per cent in females respectively; 7.6 per cent males and 8.7 per cent females had higher waist circumference than cut-off value; 21.5 per cent males and 30.5 per cent females had WHR higher than the cut-off value (Table II). Mean values of body mass index, waist-hip ratio, waist circumference and waist-height ratio was significantly higher among hypertensive than normotensive men and women (Table III).
Results of partial correlation coefficients controlled for age and sex for all the anthropometric indicators (BMI, WHR, WC, WhtR) indicated a significant positive correlation with both systolic and diastolic blood pressure; except for WHR and diastolic blood pressure where the correlation was not statistically significant. For SBP, the correlation coefficient was 0.23 with BMI, 0.23 with waist circumference, 0.11 with WHR and 0.22 with WHtR. For DBP, it was 0.13 with BMI, 0.12 with waist circumference, 0.04 with WHR and 0.11 with WHtR.
Step-wise linear regression models were fitted for systolic and diastolic blood pressure as dependent variables and BMI, WHR, WC and WHtR as independent variables controlled for age and sex to determine their influence on the variance of these dependent variables. In this study, body mass index was correlated better with both systolic (beta 0.37, SE 0.17, P
The cut-off values for all the anthropometric indicators were worked out by ROC analysis separately for male and female population to identify the risk of hypertension. The BMI cut-off for the study population was 21.7 (sensitivity = 0.870 and specificity = 0.325) and 21.2 (sensitivity = 0.831 and specificity = 0.372) for males and females respectively. For waist circumference cut-off was 72.5 (sensitivity = 0.652 and specificity = 0.632) and 65.5 (sensitivity = 0.591 and specificity = 0.630) for males and females respectively (Table IV). Figs 1 and 2 show LR for hypertension in subjects with different values of anthropometric indicator for men and women respectively. At above mentioned cut-off values for all the indicators, the risk of hypertension increased significantly (for BMI, LR=2.5, for WC, LR=1.8, for WHR, LR=2.0 and for WHtR, LR=1.7 for men) and (for BMI, LR=2.2, for WC, LR=1.6, for WHR, LR=1.3 and for WHtR, LR=1.8 for women).
Discussion
Importance of BMI, WC, WHR, WHtR have been recognized for estimating cardiovascular disease risk factors, particularly due to their positive association with hypertension18. In the present study, mean values of all these anthropometric indicators were significantly higher in hypertensive than in normotensive population in both the genders. The findings were similar to many studies19-23. We also found significant positive correlation between all these anthropometric indicators and systolic and diastolic blood pressure except for WHR and diastolic blood pressure. Many investigators have earlier reported significant positive correlation of body mass index with systolic and diastolic blood pressure24-27. Significant positive correlation between WHR and systolic and diastolic blood pressure have been reported earlier24,26,28,29. However, in our study, the correlation between WHR and DBP was not statistically significant. Woo et al30 reported that waist-hip ratio was not a useful predictor of health outcome while Dalton et al5 found that BMI, WC and WHR were equally related with hypertension. Wang et al31 reported better correlation of BMI and waist circumference with blood pressure than waisthip ratio. In contrast, Janssen et al32 reported waist circumference and not BMI explains obesity related health risk including hypertension.
In the present study, we found BMI and WC as the significant predictors of both systolic and diastolic blood pressure. Independent association between BMI and systolic/diastolic blood pressure and between waist-hip ratio and systolic/diastolic blood pressure have been reported earlier24-26,28,29. Sayeed et al33 reported that waist-height ratio was a better obesity index than body mass index and waist-hip ratio for predicting hypertension. Lin et al34 also reported that waist-height ratio may be better indicator for screening obesity related cardiovascular disease risk factors including blood pressure than BMI, waist circumference and waist-hip ratio. Zang35 reported that BMI, WC, WHR and WHtR all were positively associated with risk of coronary heart disease in Chinese women. The differences in findings may be attributed to the fact that majority of the population in the present study was non obese.
In Caucasian populations, the association between BMI and mortality is “J-shaped” and nadir of the curve between 18.5 – 25.0 kg/m^sup 2^ is taken as healthy BMI36. Cut-off values of 25.0 and 30.0 kg/m^sup 2^ are taken for overweight and obesity respectively and also for identifying the risk of associated morbidities14. In an effort to map the epidemic of obesity and associated risk of co-morbidities, it has become common practice to use these cut-off values in different populations with the assumption that different ethnic groups have similar morbidity/ mortality risk for the specific BMI level in absence of any such evidence37. Same is true for other anthropometric indicators. As evidence emerged from many studies about the higher susceptibility of Asians at lower BMI, international task force suggested lower cut-off values for them (23 and 25 kg/m^sup 2^ for overweight and obesity respectively)14. Studies from urban India38-40 suggested lower cut off values of these anthropometric indicators. The present study also suggests further lower cut-off values for the rural population and odds of having hypertension at these lower cut-off values were significantly high. Dudeja et al40 had shown a BMI of 21.5 kg/m^sup 2^ for men and 19.0 kg/m^sup 2^ for women. Snehalata et al38 suggested healthy BMI for an Indian was less than 23 kg/m^sup 2^ and cut-offs for waist circumference were 85 cm for men and 80 cm for women, and for WHR they were 0.89 for men and 0.81 for women. Indian population has higher upper body and visceral adiposity for a given BMI when compared with the Western population41. In our population, an interaction between upper body and visceral adiposity increased the risk of related morbidity such as hypertension at lower cut-off values of different anthropometric indicators38.
To summarize, rural population of Wardha had high prevalence of hypertension and low prevalence of overweight. BMI and waist circumference had strong correlation with systolic and diastolic blood pressure. The suggested low cut-off values of the anthropometric indicators will cover maximum of the population with higher odds of having hypertension and may help in reducing the mean population blood pressure levels.
Acknowledgment
The authors thank World Health Organization (India Country Office) and Government of India for providing financial assistance.
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P.R. Deshmukh, S.S. Gupta, A.R. Dongre, M.S. Bharambe, C. Maliye, S. Kaur & B.S. Garg
Department of Community Medicine, Mahatma Gandhi Institute of Medical Sciences, Wardha, India
Received November 18, 2004
Reprint requests: Dr P.R. Deshmukh, Reader in Epidemiology, Department of Community Medicine Mahatma Gandhi Institute of Medical Sciences, Sewagram, Wardha 442102, India
e-mail: prd_wda@sancharnet.in
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