Prevalence of hypertension, overweight/obesity and dyslipidemia
This epidemiological survey mainly reported considerable prevalence of hypertension (about 52%), overweight/obesity (near 48%) and dyslipidemia (over 50%), combined with low awareness of hypertension (15% only) in the representative sample of the population living in the pasture area of Xinjiang.
The Kazaks, Mongolians and Uygurs recruited in this study are herdsmen or peasants. Their ancestral allocation to the pasture area of Xinjiang goes back for hundreds of years, and they form a relatively homogeneous group with regard to socioeconomic status, occupational and dietary exposures. Few large-scale epidemiological studies have focused on the prevalence of hypertension, overweight/obesity and dyslipidemia among the minorities from the pasture area of Xinjiang in the last decade. Although the large-scale population-based survey in 1995 on the prevalence of hypertension in different ethnic groups in China [
11] reported much lower prevalence of the above-mentioned conditions, to our knowledge, most Kazaks and Uygurs involved in the study came from big cities or towns in Xinjiang, while the Mongolians were from the Inner Mongolia Autonomous Region. Therefore, different prevalences were reported in diverse populations and regions, which is a common result of epidemiological investigations. In some small-scale surveys on hypertension in Kazaks, Uygurs and Mongolians of Xinjiang, the results varied greatly. For example, a study including 119 cases [
12] showed that the prevalence of hypertension in residential Kazaks of Urumqi was 42.0%. Liu et al [
9] data showed the prevalence of Uygurs as 24.3% (264 cases) and Kazaks as 37.9% (99 cases). Data from the Hebukesel pastoral area of Xinjiang demonstrated that the detection rate of hypertension in Kazaks and Mongolians was 55.09% in 2003[
13]. In 2005, Wang et al [
8] reported in a study of 3732 Mongolians, Kazaks, Uygurs and Hans over 30 years of age in Bortala Prefecture of Xinjiang that the prevalence of overweight and obesity were 36.02% and 27.39% respectively, which was lower than that in our data. Additionally, the low awareness of hypertension displayed in the Guideline for the Prevention and Treatment of Hypertension in China (2005) was confirmed in the present study. Our data calls for the urgent need to develop effective strategies for prevention and treatment of hypertension in Xinjiang.
Associated risk factors
Our study confirmed the conventional risk factors for hypertension - age, increased BMI, hypercholesterolemia and high alcohol intake (≥30 g/d) - in all participants and specifically in the Kazak population. It is well understood that the aging process affects hypertension [
14]. Also positive association between BMI and blood pressure has been well documented [
15]. Our study demonstrates that obese individuals, classified by BMI, have significantly larger odds ratio for hypertension than overweight ones. However, we observed significant interaction effects between ethnics and overweight/obesity both for SBP as well as DBP. In particular Mongolians have the highest prevalence in overweight/obesity but the lowest prevalence of hypertension. However, the number of Mongolians included in this study is relatively small, and further research will be necessary to figure out the reasons for this observation.
The results of a 7-year follow-up study on Finnish men [
16] suggests that dyslipidemia characteristic of the metabolic syndrome predicts the development of hypertension. Although TG, HDL-C and LDL-c levels were significantly different in our four ethnic groups (Table
3) multiple logistic regression suggested that hypercholesterolemia was positively associated with hypertension in the whole population, not only in Kazaks, which indicates that hypercholesterolemia is a potential determinants of hypertension.
Numerous studies have suggested that excessive alcohol intake causes an increase in blood pressure [
17‐
21]. But in recent years, some researchers claimed that light or moderate alcohol intake might actually benefit hypertension patients [
22,
23]. Interestingly, in this study, ≥30 g/d alcohol intake was associated with hypertension adjusted for age, sex, smoking and plasma lipid level while the positive association could not be observed for an intake of alcohol <30 g/d. However, only large-scale, prospective and randomized trials might elucidate the actual role of alcohol in hypertension.
Apart from the direct influence of alcohol on blood pressure levels, one might consider that, traditionally among Kazaks, Uygurs and Mongolians in Xinjiang, alcohol consumption is associated with an increased consumption of animal fat or salted food, which could lead to an increase in fibrinogen levels. The male population in particular customarily drinks spirit to deal with the cold weather, as well as having an increased intake of animal fat and salt. Additionally, salted milk tea is enjoyed in large quantities coupled with a low consumption of vegetables, which are scarcely available in the area. Here it should be mentioned that 307 missing values of alcohol intake involved a special alcoholic beverage brewed from horse milk. Over-consumption of this may cause drunkenness, but it is difficult to assess the amount of alcohol within this specific beverage. These missing values may affect the logistic model in the statistical analysis.
Smoking is a well-known risk factor for hypertension and CVD. Association between smoking habits and BP in Japanese men [
24], negative dose-effect relationships between the amount of smoking and SBP [
25], DBP[
26] or both [
27] have been reported. On the other hand, some studies have failed to observe a significant dose-effect relationship [
28,
29]. In this study, no association was found between cigarette smoking and hypertension, for which two potential reasons should be mentioned:
1)
hardly any minority women smoke because of ethnical and behavioural restrictions,
2)
229 subjects who failed to report tobacco consumption smoke 'Mohe tobacco' (special tobacco leaves found in Xinjiang) and were considered as missing values for the logistic model.
Some general limitations should be also mentioned. First, the number of minority participants except for Kazaks was too small to allow further analysis. This is a problem when considering the differences between ethnic groups. For example, Han population of Xinjiang mostly consists of immigrants from other provinces, different in cultural background, language, reasons for migration, duration of stay in Xinjiang and age when migrating. Therefore, our conclusions cannot automatically be attributed to all Han immigrants. Second, the study was not primarily designed to compare multiple ethnics and Kazak participants, but the high percentage of residents with different ethnicities in the Xinjiang pasture area made this contingently possible. The data from Mongolians might be biased due to the rather small sample size in this study. Third, blood pressure was measured three times, but only on one occasion, which may overestimate the prevalence of hypertension. Such an over-estimation should, however, be the same in all studied groups, and single-occasion blood pressure measurements are common practice in epidemiological studies [
5,
30,
31]. Finally, we unfortunately did not have data on intake of salt and macronutrient factors that may have an impact on blood pressure [
32]. With respect to the high prevalence of hypertension, obesity and dyslipidemia found in Kazaks and Uygurs, there may be a risk of residual confounding by factors we were not able to adjust for, like e.g. the physical activity level of participants. However, keeping these limitations in mind, our study may provide a baseline database and preliminary results for further studies on the association of hypertension and its risk factors with lifestyle in different ethnic groups from the pasture area of Xinjiang.