MONDAY July 15, 2013 — Stroke is the leading cause of death in China, and it strikes Chinese people earlier in life than it does whites.
While prior studies have suggested that Asians have a greater incidence of stroke than whites, few studies have systematically quantified differences in stroke occurrence across ethnic groups. In a paper published today in the journal Neurology, Chung-FenTsai, MD, from the University of Edinburgh in Scotland, and colleagues evaluated racial differences in stroke incidence.
Additionally, they looked at differences in the types of strokes that occur across different populations (that is, ischemic stroke, intracerebral hemorrhage - bleeding, or subarachnoid hemorrhage) as well as ischemic stroke subtypes (large-artery atherosclerosis, small-vessel disease, cardioembolism, and others).
Big Data Points to Increased Stroke Risk in China
Using data from articles published over 22 years, the authors searched relevant reviews and the primary articles included in those reviews to evaluate stroke incidence. From articles describing Chinese populations, the authors identified six that met their inclusion criteria, and that included 404,254 people and 3,935 first-ever stroke cases.
These data were compared with data from a 2009 systematic review of European-origin stroke incidence studies that represented 1,885,067 people and 4,568 first-ever stroke cases. The authors found that:
- The overall stroke rate was higher among Chinese people than in white populations.
- In the 45- to 74-year-old age group, Chinese stroke incidence rate was 205 to 584 per 100,000.
- In the studies reported in whites, stroke incidence rate was lower, at 170 to 335 per 100,000.
Another interesting observation was the large variability in stroke rates across geographic regions.They found a more than fourfold difference in stroke rates across the seven Chinese cities included in one study, with the highest rates observed in the north (Harbin) and the lowest rates in the south (Shanghai). Finally, the age of onset of stroke was younger in the Chinese populations, in the range 66 to 70 years, in comparison to whites at 72 to 76 years.
Combining the earlier onset of stroke with the great incidence, these data suggest that the public health and clinical burden of stroke is greater in Chinese populations than among whites.
Potential Causes of Increased Stroke Risk
What accounts for the earlier age of onset, the greater incidence, and the greater relative proportion of intracerebral hemorrhage in Chinese populations compared to white populations?
Part of the answer may reside in the differences in the risk factors for stroke across populations. Most notable of these risk factors is hypertension, and related to hypertension, the high level of salt consumption in the Chinese diet. Differences in hyperlipidemia (high cholesterol), diabetes, smoking, socioeconomic factors, air pollution, and genetic factors are likely also to explain the excess.
Differences in the diagnosis of stroke and the pathologic subtypes of stroke are likely to be due to different diagnostic capabilities across populations, and might explain the large variability in stroke subtypes that Tsai and colleagues observed.
Subtypes of Stroke More Common in Chinese Populations
For the stroke subtype analysis, Tsai and colleagues found that the types of strokes that occur differ substantially by race. Intracerebral hemorrhage (bleeding) was much more common in community-based Chinese studies than in comparable studies in whites: 34 percent vs. 12 percent, respectively.
Intracerebral hemorrhage was also more common in China than in Taiwan; 27 to 51 percent across studies in China compared to 17 to 30 percent across studies in Taiwan.
Considering ischemic subtypes using widely accepted criteria, there was great variation in ischemic subtypes across the populations studied for both Chinese and white populations. Nonetheless, small-vessel stroke was more common in Chinese populations than in white populations.