Blood Pressure in Relation to Age, Body Mass Index and Socioeconomic Status among the Khasi Women of Sohra (Cherrapunji) of Meghalaya, India

Introduction

It is a well-established fact that high blood pressure is a leading cause of cardiovascular diseases and deaths in more developed and less developed countries. According to the World Health Organization [1], about 1.28 billion adults aged 30-79 years worldwide have hypertension, and about two- thirds of them are living in low- and middle-income countries. Many studies have also indicated an increased risk of severe or fatal COVID-outcomes including mortality among patients with hypertension [2, 3]. The prevalence of hypertension varies across regions and socioeconomic groups. In India, the prevalence of hypertension among adults aged 18 years and over increased from 22.9 percent in 2010 to 26 percent in 2017 especially in urban areas [4, 5]. Of the modifiable factors, overweight and/or obesity are considered a major factor to elevated blood pressure [6, 7]. Overweight and obesity, or excess accumulation of body fat, are defined as a body mass index (BMI) of more than 25 and 30 kg/m2, respectively [8, 9]. Many studies have shown that overweight and obesity are also associated with diabetes, renal failure, cardiovascular diseases [10] and all-cause mortality [11, 12, 13]. Epidemiological studies in developed countries have shown that excess body weight gain is attributable to the development of hypertension, and the relationship between blood pressure and BMI is almost linear [6, 14].

The basic mechanism of obesity-related hypertension is not fully understood, but it is likely that multiple pathogenetic mechanisms may contribute to the development of higher BP in obese individuals [6, 15]. Moreover, obesity-related hypertension is nothing but a relation between high blood pressure and BMI, which is also used as indicator of underweight (BMI= < 18.5 kg/m) due to chronic energy deficiency or low body fat percentage [8]. Therefore, it is unclear whether the relation between blood pressure and BMI is linear or non-linear particularly in less developed countries like India where both underweight and overweight coexist. Moreover, BMI may also vary according to socioeconomic development or demographic transition [16, 17, 18]. Previous studies and reviews in Northeast India [4, 5, 19] have suggested that changes in dietary and physical activity patterns associated with urbanization are likely to predispose many individuals to being overweight, obese, diabetic, and hypertensive. In the present study, an attempt has been made to analyze our findings on blood pressure in relation to age, body mass index, and socioeconomic status among the Khasi women in the state of Meghalaya, India.

Materials and Methods

The present study was conducted among the Khasis of Sohra (Cherrapunjee) area in the East Khasi Hills district of Meghalaya, India. A cross-sectional sample of 705 non- pregnant mothers aged 15-50 years. An informed consent was obtained from each of the 705 participants before the commencement of the study. Anthropometric measurements, such as height and weight were taken following standard techniques [20]. Body mass index (BMI)= weight (in kilograms)/height (in square meters) was used to assess the nutritional status, and BMI categories were classified as < 18.5 kg/m2, 18.5 to 22.9 kg/m2, and ≥ 23 kg/m2 as underweight, normal weight, and overweight/or obese [21].

Data on socioeconomic and demographic status were based on education level and on per capita monthly income of households collected directly from each participant, using appropriate schedules. The socioeconomic status was based on percentile distribution of per capita monthly income as follows: Above 75th percentile (> Rs 2778) = High Income Group 50th to 75th percentile (Rs 2000 - Rs 2778) = Middle Income Group Below 50th percentile (< Rs 2000) = Low Income Group. Blood pressure was recorded, using a standard mercury sphygmomanometer and a stethoscope by taking the mean of three readings that were taken five minutes apart [22]. Systolic blood pressure (SBP) was recorded as the first Korotkoff sound, and diastolic blood pressure (DBP) was recorded when the Korotkoff sound disappeared [23]. All measurements were taken on the left hand of the participant. Each participant was asked to relax and take rest for about 10 minutes before taking the measurement. Untreated blood pressure values of SBP 120- 139 mm Hg and/or DBP 80-89 mm Hg were classified as pre- hypertension, whereas hypertension was defined as SBP ≥ 140 mmHg and/or DBP ≥ 90 mm Hg [24]. Mothers with SBP of < 90 mm Hg or DBP of < 60 mm Hg were considered as hypotensive.

Data were managed and analyzed using Statistical Package for the Social Sciences (SPSS, version 26) software with a level of significance at five percent. The results were presented into two broad age groups, namely younger mothers (< 30 years) and older mothers (≥ 30 years). Descriptive statistics were generated in terms of sample size, percentage, mean, and standard deviation. Student t-test was used to test the differences between two means. Categorical variables like hypertension, nutritional status, and socioeconomic status were summarized by count and percentages. Chi-square (χ2) test was used to test if there was any relationship between hypertension and other independent variables. Karl Pearson’s coefficient of correlation (r) was used to test the linear relationship between two continuous variables. Stepwise-multiple regression analysis was carried out for testing the strength of association between age- adjusted systolic blood pressure and other independent variables like anthropometric, nutritional, and socioeconomic status.

Results

Table 1 gives the means and standard deviations of the anthropometric measurements and blood pressure for the younger and older mothers aged < 30 and ≥ 30 years, respectively. The older mothers were significantly heavier than younger mothers in body weight (t = 2.53, p < 0.01) and BMI (t = 2.90, p < 0.01), and the relation between age and BMI was positively significant (r = 0.131, p < 0.01). There were also significant differences between older and younger mothers in respect of both systolic blood pressure (t = 3.30, p < 0.001) and diastolic blood pressure (t = 5.36, p < 0.0001).

The relation between age and blood pressure was positively significant for both systolic blood pressure (r = 0. 175, p < 0.01) and diastolic blood pressure (r = 0.236, p < 0.01), Systolic blood pressure (mmHg) 109.91 12.93 113.54 16.14 3.30 Diastolic blood pressure (mmHg) 68.7 11.18 73.49 12.05 5.36

When classificatory categories of BMI and blood pressure are used as indicators of the nutritional status and hypertension, Table 2 shows that about 13% and 30% of women were underweight and overweight, respectively. It was also observed that the prevalence of underweight was higher among younger mothers (15%) than among older mothers (12%), although it was not statistically significant (χ2 = 1.74, d.f. = 1, p > 0.05). Similarly, the prevalence of overweight and/or obesity was statistically higher (χ2 = 6.75, p < 0.01) in older mothers (34%) compared to their younger counterparts (25%). The prevalence of hypotension, prehypertension, and hypertension were 12%, 23%, and 9%, respectively, for mothers of all groups. The prevalence of suggesting that blood pressure increased with advancing age.

Characteristics < 30 years (n = 296 ≥ 30 years (N= 409 t-value (2-tailed) Mean SD Mean SD Weight (kg) 44.23 7.78 45.76 8 2.53* Height (cm) 143.64 5.57 143.57 5.07 0.17 BMI (kg/m2) 21.39 3.28 22.15 3.37 2.90* hypotension was about 16% among mothers below 30 years of age, which was significantly higher compared to their older counterparts (χ2 = 13.74, d.f. = 1, p < 0.001). However, older mothers had a higher prevalence of prehypertension and hypertension than younger mothers (χ2 = 12.85, d.f. = 1, p < 0.001). Table 2 also shows that the prevalence of hypertension (11%) among mothers aged 30 years and over was higher than among younger mothers (5%). The underweight and hypotension prevalence was higher in younger mothers than in older mothers. In contrast, the prevalence of overweight and elevated blood pressure was higher in mothers aged 30 years and older.

Table 2 further shows that about 48% of the women included in this study belonged to the low income group. The proportion of women in the low-income group was significantly higher in the older age groups compared to the younger age groups (χ2 = 20.64, d.f. = 1, p < 0.001). Similarly, the proportion of women with primary level of education was significantly lower in the younger age group compared to the higher age groups (χ2 = 11.76, d.f. = 1, p < 0.001).

Table 3 shows the results of the regression analysis of age-adjusted SBP in relation to anthropometric, nutritional, and socioeconomic factors. The marginal effects of socioeconomic status in terms of household income and educational levels were not statistically significant after adjusted for age. Adjusted for age, about 11% (R2 = 0.110) and 10% (R2 = 0.10) of the variation in SBP was due to body weight and BMI, respectively. The regression slope was, however, negatively significant (β = -5.175 ± 1.650, t = 3.14, p < 0.002), indicating that younger women had, on average, about 5.18 mm Hg lower age- adjusted SBP than those with normal BMI. However, when overweight was included in the model as binary variable relative to normal BMI, the negative association between underweight and low SBP was no longer significant (β = -3.060 ± 1.673, t = 1.82, p > 0.05). In other words, the effect of being underweight on age-adjusted SBP disappeared when overweight was included in the model, indicating that overweight women had, on average, about 6.31 mm Hg higher age-adjusted SBP than underweight women in the present study (β = 6.31 ± 1.123, t = 5.12, p > 0.0001).

1-Underweight adjusted for age; 2-Underweight adjusted for age and overweight and/or obesity; 3- Overweight adjusted for age. Table 3: Regression analysis of age-adjusted systolic blood pressure in relation to anthropometric, nutritional, and socioeconomic variables.

Table 4 shows the similar results of the regression analysis of age-adjusted DBP to those carried out for age- adjusted SBP. The marginal effects of both household income and educational levels were not significantly associated with age-adjusted DBP. About 12.3% (R2 = 0.123) and 11.8% (R2 = 0.118) of the variation in DBP was attributed to body weight and BMI, respectively. The Table shows that the regression slope for the age-adjusted DBP was inversely significant with underweight (β = -3.237 ± 1.298, t = 2.49, p < 0.013), suggesting that underweight women had lower age-adjusted DBP than women with normal BMI. Similar to age-adjusted SBP, the significant association between underweight and low DBP disappeared when overweight was included in the model (β = -1.589 ± 1.316, t = 1.21, p > 0.05). On the other hand, the results show that the age-adjusted DBP was positively associated with overweight (β = 4.916 ± 0.970, t = 5.07, p < 0.0001), indicating that overweight mothers had, on average, about 4.92 mm Hg higher DBP than mothers with normal BMI.

1-Underweight adjusted for age; 2-Underweight adjusted for age and overweight and/or obesity; 3- Overweight adjusted for age. Table 4: Regression analysis of age-adjusted diastolic blood pressure in relation to anthropometric, nutritional, and socioeconomic variables.

Discussion

The present findings indicate that older mothers were significantly heavier than their younger counterparts in respect of body weight and BMI. It was found that the prevalence of underweight was higher among younger mothers than among older mothers, although it was not statistically significant. Similarly, the prevalence of overweight and/or obesity was statistically significant higher in older mothers compared to younger mothers. There were also significant differences between older and younger mothers in respect of DBP and DBP, and both SBP and DBP increased with advancing age. Overall, the present findings are consistent with those earlier studies and reviews, suggesting that blood pressure increases with increasing age and BMI [6, 14, 25, 26].

However, the present findings may be interpreted with caution. Recent studies of South Asian populations have shown that BMI was not much associated with vascular mortality [27], although elevated BMI is associated with increased systolic blood pressure [28, 29], despite some inconsistencies [30]. The relationship between BMI and morbidity and/or mortality has been shown to be non-linear even those reported from developed countries [31, 32]. Depending upon the type of statistical analysis used in a given study, different interpretations can be made from a given dataset on the relation between BMI and morbidity or mortality [33]. BMI is a crude measure of overweight and obesity, and it is also an indicator of underweight-related morbidity and mortality, which is in turn related to ethnicity and socioeconomic factors within and across populations [8, 34]. An excess accumulation of body fatness also varies between ethnic and socioeconomic groups, and many studies have supported that the cut-offs are too high for South Asian populations which have a greater risk of cardiovascular and metabolic diseases even at a lower level of BMI [17, 21, 35, 36].

The present study also indicates that the prevalence of underweight as well as hypotension was higher in younger mothers than in older mothers, whereas the prevalence of overweight with elevated blood pressure was higher among mothers aged 30 years and older. The stepwise multiple regression analysis on age-adjusted SBP and DBP suggests that younger women had, on average, lower blood and hypotension than those with normal BMI. However, the marginal effects of being underweight on blood pressure disappeared when overweight was included in the model, suggesting that overweight mothers had, on average, higher blood pressure than mothers with normal BMI. Therefore, it is likely that age- adjusted blood pressure may not be positively correlated with BMI below the normal level. Subject to further studies with larger sample sizes, the present study indicates that underweight mothers had higher prevalence of hypotension than those with normal BMI. It is likely that the positive correlation between BMI and blood pressure may predominantly be due to elevated blood pressure at higher BMI levels, especially in populations with decreasing proportion of underweight due to a rapid increase in overweight and obesity. Our findings may also have certain implications for the relation between underweight and other morbidities including infections, anemia, osteoporosis, sarcopenia, anorexia nervosa, strokes, myocardial infarction, health quality of life, disabilities, and other adverse health outcomes of undernutrition [37, 38].

Our findings are also consistent with some other studies from less developed countries where hypertension is associated with overweight and/or obesity, whereas hypotension or low blood pressure is correlated with underweight [39, 40], thereby indicating that blood pressure does not increase at all levels of BMI as observed among some tribal populations in India [41]. Further, the marginal effects of both household income and educational levels were not significantly associated with age-adjusted blood pressure, suggesting that other lifestyles and dietary factors may be associated with elevated BMI and blood pressure [19, 42, 43, 44].

Conclusion

The present findings indicate that older mothers had higher BMI and blood pressure. The prevalence of underweight as well as hypotension is higher in younger mothers than in older mothers. On the contrary, the prevalence of overweight, along with elevated blood pressure, was higher in older mothers aged 30 years and over. The marginal effects of both household income and educational levels were not significantly associated with age-adjusted blood pressure, suggesting that other lifestyles and dietary factors may be associated with elevated BMI and blood pressure. The age-adjusted SBP and DBP indicated that younger women had, on average, lower blood pressure and hypotension than those with normal BMI. However, the marginal effects of underweight on blood pressure disappeared when overweight was included in the model, suggesting that the effect of underweight on blood pressure was suppressed by the greater effect of overweight and obesity. This finding may have certain implications for populations in less developed countries with higher mean values of BMI due to change in life-styles associated with increasing urbanization and socioeconomic development.