Blood cholesterol level and risk of stroke in community-based or worksite cohort studies: A review of Japanese cohort studies in the past 20 years

Evidence of the causal relationship between hypercholesterolemia and coronary artery disease (CAD) has been established worldwide. However, little attention has been paid to the relationship between hypercholesterolemia and stroke, despite stroke being the most common cardiovascular disease in Japan. We therefore reviewed cohort studies that investigated this relationship in the Japanese population over the past 20 years, and compared their findings with clinical trials and cohort studies in Western countries. Fourteen cohort studies were carried out in Japan during this period. The number of subjects in the studies ranged from 1621 to 91,219 and the mean follow-up period ranged from 7.6 to 32 years. The majority of studies showed no association between hypercholesterolemia and total stroke. However, one report showed a positive association between low-density lipoprotein cholesterol and atherothrombotic cerebral infarction. The relationship between hypercholesterolemia and cerebral infarction may be modified by the proportion of atherothrombotic infarctions in the population surveyed. Randomized controlled trials on statins have shown a substantial reduction in cerebral infarction, and so the discrepancy between cohort studies and clinical trials requires further study. However, some studies have reported that subjects with low blood cholesterol are more susceptible to intracerebral hemorrhage. Two hypotheses have been proposed to explain this association between low cholesterol and intracerebral hemorrhage. First, low blood cholesterol may induce angionecrosis, possibly in combination with hypertension, and second, low blood cholesterol may reflect a poor nutritional status. Either way, further continuous research in various fields of medical science is required to clarify the overall effect of blood cholesterol on stroke in humans.