This is the first time a Chinese medical team has reached the hinterland of the Taklamakan Desert to perform medical examinations and collect data on the health status of minorities of communities of Rob descent in China. The Desert community is a completely isolated subgroup of the Uyghur population living in the hinterland of the Taklamakan Desert, which is the largest desert in China. They were not known until 1989, when the Hotian area government found them and named the community the Daliyabuyi township, which was formally taken under Hotian government jurisdiction. The Yuli Rob community share a common ancestor with the Desert community, the Rob people. When the Lop Nur river dried up, the Rob people living in the surrounding area migrated and scattered afar, with the Desert group going south of Lop Nur, while the Yuli Rob group moved westward, migrated to Yuli county, and settled along the Tarim River shore (the biggest interior river in China). The Yuli Rob people have kept their traditional semi-isolated lifestyle, and one of the three survey sites still has no high roads or electricity. The third group included in the study was the Turpan minority, living in the Turpan Depression, the second lowest continental point in the world. Compared with the first two groups, the Turpan minority live in a more open environment, and mix with the Han population in the same village though they do not intermarry with the Han.
We observed that the three subgroups, with different economic statuses, natural environment and lifestyles, also displayed unique distributions of some CVD risk factors. First, there were almost no drinkers and only a small proportion of smokers in our subjects, which is different from the habits of most Uyghurs, indicating that the isolated communities have little interaction with the outside world. Second, there was a markedly lower level of HDLC in Desert subjects and a markedly higher level of HDLC in Turpan subjects, resulting in significantly different patterns of the TC:HDLC ratio, which is commonly used as a predictor of cardiovascular incidents and death,16
suggesting different possibilities for the role of HDLC in the elevated risk of CVD in the two subgroups. Third, unlike other studies wherein a reduction in HDLC levels was commonly observed in subjects in the Chinese Han population who had features of metabolic syndrome (eg, high blood pressure, obesity, diabetes, etc),18
the Desert group showed a different relationship between HDLC levels and BMI and serum FBG levels. For BMI <25, 25–29 and ≥30.0 kg/m2
, the mean HDLC was 0.63, 0.61 and 0.74 mmol/l, respectively, in the Desert group (p=0.3489). For serum FBG <7.0 and ≥7.0 mmol/l, the mean HDLC was 0.75 and 0.61 mmol/l, respectively, in the Desert group (p<0.0001). This trend was opposite to that in other studies and was also found in another study conducted in a rural Uyghur population in the Hetian area. The reason for the difference is yet to be determined.20
Finally, Yuli Rob subjects possessed a higher prevalence of overweight or obesity and hypertension compared with Desert and Turpan subjects. For example, 38.3% of the Yuli Rob subjects with BMI in the normal range (BMI <25 kg/m2
) suffered from hypertension, which was 2.5-fold and 3.6-fold higher than Turpan and Dessert subjects, respectively. Moreover, we also observed that hypertension in the Yuli Rob population was more common in the younger group (age <40 years) compared with that of the two older groups, indicating that other factors, other than age and BMI, may contribute to the high prevalence of hypertension in this subgroup.
Some issues are worthy of discussion according to the observed intergroup differences in the CVD risk factor profile. First, there are unique dietary differences: for generations the Desert people, living in the hinterland of the Taklamakan Desert, have had no choice in their lifestyle, with animal husbandry providing a living. They face adverse conditions with limited nutritional resources, lack of fruits and vegetables and little carbohydrates, resulting in low body weight, low serum lipid profiles and a low prevalence of hypertension. In contrast, the Yuli Rob people in the fertile Tarim River area fish and farm for a living, with their diet including more pasta and meat. They had higher levels of lipid risk factors, overweight and a higher prevalence of hypertension. The Turpan people live in a more open environment, and the area is famous for grape production. Therefore, besides a normal diet like the Yuli Rob people, the Turpan people had more fruit consumption. Thus, although there was a high prevalence of overweight, which is a characteristic of subjects of Uyghur origin, they had a much lower prevalence of high TC:HDLC ratios and hypertension compared with that of Yuli Rob subjects. These variations are also illustrated by another study of Yi minority ethnic migrant groups in south China, where environmental changes from altered lifestyles are superimposed on genetic influences.17
Second, the environmental conditions differed widely across three subgroups. The Yuli Rob population is located about 2000 m above sea level, while Desert and Turpan populations live in extremely hot climates. As temperature decreases about 1°C for each 150 m increase in altitude, at 2000 m the temperature is roughly 14°C lower than that at sea level. Some studies reported that chronic exposure to hypobaric hypoxia at a median altitude increases parasympathetic and sympathetic tone in healthy subjects, and is significantly associated with an increase in BP,21
while other studies suggested that after years of residence at high altitude, BP may actually be lower than that observed among residents at sea level.23
Our data showed more hypertension in Yuli Rob subjects at a younger age and in those with BMI in the normal range, but whether this elevation in BP has some relationship with altitude needs further investigation. Furthermore, there was no evidence from previous studies24–26
that hot, dry climates may have an effect on BP in healthy subjects, suggesting that when the same gene pool is confronted with different environments, the conventional risk factors play a major role. The challenge of preventing CVD diseases lies in identifying and addressing the components most relevant to each community at their present and projected levels of CVD risk.
An assessment of the pattern of risk factors for CVD in rural minority populations is important for several reasons. First, despite rapid urbanisation in China, most Chinese minority populations still live in rural areas and, as with any Han rural population, they have limited access to healthcare and can least afford to pay for the high treatment costs associated with chronic conditions, especially those who live in remote and isolated areas. Estimation of the distributions of the risk factors in these populations is vital for planning public health policies. Second, unlike the epidemic of CVD in developed countries, which was driven mainly by urban migration, the current epidemic in developing countries may also be affected by increasing globalisation—greater interconnectedness of populations leading to a growing uniformity of lifestyles in both urban and rural areas.27–29
Unlike urban areas, the prevalence of risk factors for CVD in remote rural areas is less likely to be confounded by the effects of urban migration. Third, such data may contribute to our understanding of disease aetiology, since comparison of the geographical distributions of the prevalence of risk factors and diseases may allow the relative contributions of genes and the environment to be explored.27
There are some potential limitations in our study: (1) in the specific natural environment, we were unable to implement random sampling, therefore the non-probability sampling design method and participation of less than half of those eligible raises the possibility of selection bias; (2) there was simple categorisation of cholesterol as ‘normal’ or ‘abnormal’, BP as ‘hypertensive’ or ‘normotensive’, and FBG as ‘diabetic’ or ‘non-diabetic’, as in other studies. The risks associated with these and other factors operate on a continuum. Limited categories tend to ignore the substantial risks contributed by these factors below the clinical threshold, that is, even within the so-called normal range30
; (3) because this is the first examination of isolated populations and semi-isolated populations, there were no data available on the personal medical history of the participants, which might result in misclassification of hypertension and diabetes; (4) Yuli Rob subjects were much older than the other two groups, which may also be part of the reason for higher BP and higher blood cholesterol, although in most cases our analysis was adjusted by age; and (5) there were higher blood sugar levels compared with other studies.20
The reason for this needs further investigation.
In summary, because of the non-probability sampling design of the study and its low response rate, the results are unlikely to be conclusive. Nevertheless, our data indicate that epidemiological analyses in specific ethnic populations can identify unique CVD risk factors, which are likely to be very important in the development of tailored strategies for the prevention of CVD.