In this study, the prevalence of hypertension increased with rising BMI and WC in the older population of Xinzheng, China, in males and females and in the entire study population. These associations remained significant after adjustment for multiple factors and restricted cubic spline analysis showed clear dose-response relationships. To our knowledge, this is the first study to research the association between BMI, WC and hypertension risk in an older Chinese population. At the same time, this study conducted an additive interaction analysis, which concluded a significant additive interaction between BMI and WC such that the prevalence of hypertension increased. To some extent, this study provides a better understanding of the association of anthropometric indicators of obesity with hypertension rather than focusing on individual indices, which would be more enlightening for hypertension prevention.
Our results are consistent with most previous studies that showed that the risk of hypertension increases with rising BMI [14, 19]. The “Look up 7+” epidemiological study showed that blood pressure increased significantly across BMI levels, which indicated that there was not only a strong relationship between BMI and hypertension, but also an association between the continuous variables of BMI and blood pressure. Our study confirmed that there was a nonlinear dose-response relationship between BMI and the risk of hypertension, which was similar to previous studies [21, 22]. However, a prospective study including 1412 subjects provided evidence that an increase in BMI is associated with a linearly increased adjusted risk of developing conditions with high hypertension risk, possibly because of estimating the relationship using categorical measures of BMI, masking the shape of the dose-response relationship. Furthermore, in our large sample (n = 126123), BMI below 25 kg/m2 was regarded as a healthy weight for the elderly in terms of hypertension prevalence. However, our proposed appropriate level for hypertension were higher than those in some previous studies, which could be due to differences in the age range. The average age we sampled was much higher because BMI is greater in older populations, which might be a reason for the inconsistent findings, and when one of the studies stratified data by age (< 50 and ≥ 50 years), the appropriate level for the older group was ༜25 kg/m2 for men and women. Contrary to the three studies above, the NHANES study suggested 27 kg/m2 as the value , but there may be innate or cultural differences between the U.S. and Asia, including dietary habits, macronutrient content, and physical activity habits. Given the marked variations in different world regions, countries and populations within countries, the use of unified range may underestimate or overestimate the health hazards; thus, it is of great interest to determine the appropriate level for cardiovascular disease risks.
For WC, the relationship with hypertension was reported by most studies [28, 29]. Most studies have found a positive association between WC and hypertension, whereas a null association was found in a prospective study from European populations. The low participation rate and the relatively high study drop-out rate may bias the result. We highlighted the increased risk of hypertension when WC was over 88 cm and 86 cm for males and females, respectively. Our proposed WC appropriate level is higher than those reported by M Gus et al. As early as 2009, they suggested that the best range to predict hypertension were ༜87 cm in men and ༜80 cm in women, and increasing WC over time could be the cause of the difference. The worldwide upward trend in obesity has been dramatic; from 2013 to 2018, the mean WC increased from 82 cm to 86.3 cm for men and from 79.1 cm to 83.4 cm for older women . However,lower appropriate level were suggested by previous studies[33, 34], and ethnic and racial differences might explain the discrepancy between different studies.
In China, rapid economic development and associated dramatic lifestyle changes have led to a substantial increase in the prevalence of obesity and related noncommunicable diseases, including cardiovascular diseases, which is concerning for a developing country with a population of 1.37 billion. To our knowledge, the present study is the first to report a synergistic effect of higher BMI and WC on the risk of hypertension in the aged. In other words, the copresence of higher BMI and WC greatly increased the risk of hypertension, more than the summation of the risks due to exposure to either of them. In a cohort of 17,803 pregnant Chinese women, the copresence of a higher BMI and WC interacts to further increase the risk of gestational diabetes mellitus . In addition, RISKESDAS research showed that only when general obesity or overweight coexisted with central obesity was the prevalence of hypertension significantly increased . This finding supported the stable relation between excess body fat and blood pressure. It is generally believed that the increased body mass would raise blood volume and cardiac output and then lead to the inadequate vasodilatation while the increased activity of the sympathetic nervous system, abnormal rennin-angiotensin-aldosterone relation and insulin resistance would arouse defects in the control of vascular resistance. These adverse vascular responses may dominate the development of obesity-associated hypertension [36, 37].
Several additional points warrant discussion. First, the findings of this cross-sectional study are not conclusive evidence of a causal relation of WC and BMI with hypertension. Thus, we must be cautious in interpreting the present results, and further cohort studies are needed to clarify our findings. Second, as the study data come from the Chinese middle area among the older population, our proposed appropriate level for the indices are only valid for this population. Third, selection of the appropriate levels for BMI and WC for hypertension was based on visual checking of the shapes of the OR curves. The true appropriate level of BMI and WC for hypertension remained arbitrary and might deviate slightly from the selected values. However, to the best of our knowledge, our study is the first to explore the association between anthropometric Indicators of obesity and hypertension among older people with a large sample size in central China, and it is of practical significance to improve relevant research. Second, this study is based on a comprehensive health check-up program, which not only contains data related to physical measurements and disease, but also includes information on demographic characteristics, physical activity, daily living habits and some blood biochemical tests, therefore, we can make full use of this information for a more comprehensive and reliable analysis.