Self-reported hypertension in Northern China: a cross-sectional study of a risk prediction model and age trends

Hypertension (HTN) is a worldwide non-communicable disease epidemic and leads to further disabling comorbidities such as atherosclerosis, chronic kidney disease, and cardiac failure [1, 2]. The World Health Organization reported that HTN affected more than one billion people worldwide in 2010. Furthermore, HTN has led to the death of 9.4 million people and contributed to 7.0% of the global disability-adjusted life years, resulting in HTN being ranked third in terms of the global burden of disease [3]. Four large-scale population surveys have reported HTN rates in 1993, 1998, 2003 and 2008 were 5.11%, 7.73%, 13.58%, and 18.8%, respectively [4]. Although these previous findings indicate a lower prevalence in China than the global average, the total prevalence of HTN has increased over time. Many factors have been reported to be associated with HTN among residents of Inner Mongolia, including comorbidities, socioeconomic factors, and lifestyle characteristics, such as diabetes, age, drinking, body mass index (BMI, weight in kilograms divided by height in meters squared), and dietary habits [5‐9]. However, the exact role and effect value of these factors in predicting HTN remain unclear.

Inner Mongolia is located in northern China, covering a large area and great diversity in terms of geographical climate, lifestyle, and demographic characteristics. Inner Mongolia is a multi- ethnic region, the majority population is Han Chinese. Han and minority groups have different cultural backgrounds, customs and lifestyle. Minority are more likely to eat more animal fat, milk products, drink strong wine, consume less fresh vegetables and fruits. Because the annual cold season is longer in this region than in other areas of China, Inner Mongolia is characterized by a lack of intake of fresh fruits and vegetables, a preference for pickled food, a high salt intake (> 20 g per day), and a high prevalence of smoking and drinking [10, 11]. In addition, because of a lack of local economic development, the level of culture and education are generally lower than other areas of the country, the level of medical care is poor, and residents lack awareness of health care, leading to poor public health conditions in terms of chronic diseases.

Studies from many countries have shown that lifestyle and public health interventions among different populations have consistent effects regarding the improvement of HTN [12], but there is no scoring system for assessing the risk associated with socio-demographic and health related factors. Therefore, a study exploring the self-reported HTN risk score among the residents of Inner Mongolia is required as part of the effort to reduce the HTN prevalence. The objective of this study was to assess the effect of a calculated risk score on self-reported HTN among the residents of multi-ethnic in Inner Mongolia.

This study identified predictors significantly associated with self-reported HTN. Being female and minority groups were independent risk factors for self-reported HTN among residents of Inner Mongolia. The factor with the highest contribution to the risk score for self-reported HTN was being aged ≥71 years, which contributed 12 points to the risk score, on average. The risk prediction model showed a good predictive accuracy for self-reported HTN. This model is potential to have a positive effect on health services in Inner Mongolia, where both the economy and the healthcare conditions are relatively underdeveloped.

Several methods for assessing the risk of different diseases have previously been developed [14‐16], but we found the optimized Framingham risk score model to be particularly valuable in our study. The Framingham Heart Profile (FHP) is currently applied worldwide in the assessment of various diseases [17], including coronary heart disease, metabolic syndrome, HTN, and tuberculosis [6, 18‐20]. However, there are several limitations associated with directly applying the FHP [21] in Inner Mongolia, an autonomous region that is ecologically diverse and has residents of various minority groups with distinct regional and ethnic characteristics. Therefore, we used an optimized FHP to evaluate the risk of self-reported HTN among Inner Mongolia residents. The optimized FHP can serve as a readily available and useful tool that the majority of medical staff members and residents can use in the assessment of the risk of self-reported HTN and in identifying high-risk groups.

In this study, we suggested that age was a major risk factor for self-reported HTN among residents of Inner Mongolia. The risk of self-reported HTN increased by 0.07 (95% CI: 1.07, 1.08) unit for every one-year increase in age. Compared with residents aged < 30 years, the risk of self-reported HTN was higher among the other age groups. Of all of the risk factors examined, being aged ≥71 years was associated the highest addition to the risk score (12 points) for residents. This finding is consistent with reports from global epidemiological research, as well as results obtained in other parts of China [7, 22]. The result is mainly explained by factors such as arterial stiffness, thickness, loss of elasticity, and stenosis of the aorta and arterial wall among elders. In addition, older people are more likely to take less physically active and have more functional disorders [23, 24] that increase the risk of HTN.

Several studies have found that the risk of HTN is much higher among male than female [25, 26]. However, our study demonstrated that female was an independent risk factor for self-reported HTN among residents of Inner Mongolia. The risk score of female self-reported HTN was 1, corresponding to a higher risk (OR: 1.22, 95% CI: 1.08, 1.37). The difference in results between the present study and past findings may be related to differences in the sociocultural background of the study population, which lead to different psychological stresses. In China, people’s ideology is relatively conservative, in parallel, men and women are not equal in social or economic status. Although significant changes have accompanied economic development, many women still suffer from the greater stress. In such situations, the risks of developing physical illnesses and endocrine disorders because of various stresses are higher among women than men [27], which increase the risk of HTN or other chronic diseases. Our findings also revealed the distribution of risk factors of self-reported HTN and baseline characteristics on gender, which can help to identify that the female is an independent risk factor of self-reported HTN, which is not resulted due to self-reported bias. We found risk factors of self-reported HTN mainly concentrated in female, especially, proportion of female was higher than male in minority groups, female have a higher possibility in a low socioeconomic status and with comorbidity. These indicted the distribution of risk factors between self-reported HTN and female are consistent. The detailed information sees Additional file 5: Table S4.

Additionally, our study showed that married or widowed/divorced were independent risk factors for self-reported HTN, contributing 4 and 2 points to the risk score, respectively. This corresponded to a higher risk of self-reported HTN among residents of Inner Mongolia who were married (OR: 2.05, 95% CI: 1.42, 2.95) or widowed/divorced (OR: 1.82, 95% CI: 1.22, 2.72). The associations of culture, social and economic status, and marital status with the presence of chronic disease have been confirmed in several countries [28‐30]. The findings of the present study suggested that female residents who married or widowed/divorced continue to experience serious work- and life-related stresses in Inner Mongolia.

A major finding of our study was that minority groups was an independent risk factor for self-reported HTN among residents of Inner Mongolia: The risk scores of Hui, Mongolian, and other minority status were 1, 1, and 4, respectively, corresponding to the ORs were 1.37 (95% CI: 0.79, 2.36), 1.15 (95% CI: 1.00, 1.33), and 1.66 (95% CI: 1.29, 2.13), respectively. Minority groups generally live in the eastern part of Inner Mongolia, which may explain the relatively higher rate of self-reported HTN in this region. In the United States, a 2005 survey conducted by the National Center for Chronic Disease Prevention and Health Promotion of the Centers for Disease Control and Prevention [31] showed that the age-adjusted self-reported HTN prevalence was 40.5% among non-Hispanic blacks and 27.4% among non-Hispanic whites. Our finding of ethnic disparity in self-reported HTN prevalence suggests that race may be an important risk factor. The Han and the minority populations in Inner Mongolia often have different lifestyles. Previous studies have demonstrated that dietary habits, genetics, and enduring lifestyle factors are associated with HTN [8, 32, 33]. Minority population often eats an unbalanced diet (e.g., excessive consumption of sodium, beef, mutton, and alcohol) [34‐36]. The present study suggested that the risk score for self-reported HTN among drinkers in Inner Mongolia was 1, with a corresponding OR of 1.19 (95% CI: 1.01, 1.32). The long-term consumption of alcohol increases the risk of HTN by increasing the risk of arterial wall stiffness, which further lead to vascular atherosclerosis, cardiac disease, and cerebral vascular disease [37]. A study published in The Lancet indicated that low- and lower-/ middle-income countries contribute nearly two-thirds of the burden of chronic disease [38], which is consistent with our finding that the rate of self-reported HTN is higher among those living in poverty. Those living in poverty often have low levels of education and unhealthy lifestyles [39]. Future public health measures should be aimed at decreasing the prevalence of self-reported HTN among minority populations in Inner Mongolia by emphasizing prevention and improving control.

We also evaluated the association between BMI and self-reported HTN. Consistent with other studies, our study suggested that high BMI was an independent risk factor for self-reported HTN among residents of Inner Mongolia, with a risk score of 3 points and a corresponding OR of 2.49 (95% CI: 2.25, 2.77). In the Framingham Study, systolic blood pressure was found to increase 7 mmHg with a 10% increase in body weight in the majority of the population [40]. The JNC-7 report [41] recommends lifestyle improvements for all patients with prehypertension, including lose weight and increase exercise. We recommend focusing on high BMI as a target to implement proper interventions for the prevention and control of HTN.

Our study implied that comorbidity was also an independent risk factor for self-reported HTN among Inner Mongolia residents. Comorbidity had a self-reported HTN risk score of 2, with the corresponding OR of 2.06 (95% CI: 1.82, 2.34), compared with residents with no comorbidity. We also suggested increased risk of self-reported HTN was associated with more severe depression and old age, which was consistent with Jonas’s [42] finding that the incidence of HTN was higher among people with anxiety and depression who aged 45–64 years than low anxiety/depression scores. Bakris GL et al. found diabetes can increase incidence of HTN, and several antihypertensive agents are required to control blood pressure in patients with diabetes [43]. Routine screening for self-reported HTN among patients with comorbidities will likely help to earlier detection and treatment of HTN as well as improve clinical outcomes.

Despite the limitation, the study strengthens the understanding the relation of self-reported HTN with basic socio-demographic and clinical factors and among Inner Mongolia residents. Applying an optimized Framingham risk model could early screen the high-risk groups of self-reported HTN. Efforts to prognosis and prevent self-reported HTN in Inner Mongolia, especially multi-ethnic regions.