Low cholesterol increases stroke risk
Part 1: Introduction
Stroke is defined as the sudden rupture or blockage by clotting of a blood vessel to or within the brain. Symptoms of stroke can range from minor dizziness or momentary temporary loss of function that is barely perceptible to paralysis or death. Strokes were generally confined to the very elderly, but recently strokes are being increasingly seen in younger people.
Asians traditionally eat a diet which is poor in animal products; they have low levels of cholesterol in their blood — and have a very high level of strokes. Japanese scientists believed that their diet could be the cause of their high stroke risk. United States scientists, on the other hand, were sceptical of the possibility, believing that there were few if any risks associated with low blood cholesterol. This difference in viewpoint was thought worthy of further investigation to resolve the question.
Because medical trials are expensive, they tend to involve only a relatively small number of people. But there are exceptions. One such arose after World War II, when Japan's eating habits, influenced by American dietary habits, changed dramatically: from 1958 to 1995 fat consumption increased four-fold and animal protein intake in the form of meat, eggs and dairy products increased by 22%. At the same time, they ate less rice.
Not unexpectedly, cholesterol levels rose — by an average 22 mg/dL (0.57 mmol/L) in men and 29 mg/dL (0.75 mmol/L) in women.
This change of circumstances after the war was a perfect opportunity for scientists to witness any changes in disease patterns that this change of diet would bring.
They found that it brought dramatic benefits. During the period, cholesterol levels rose from an average of 150mg/dl to 192mg/dL (3.9 mmol/l to 5.0 mmol/l), and the numbers of strokes of both types fell by 85 % from 1344 to 205 per 100,000 per year.
Deaths from cerebral haemorrhage also declined by 65% in men and 94% in women aged 40-69.
And, even though blood cholesterol went up, there was no increase in heart disease deaths in either sex.
The authors conclude that the benefits to health in Japan were a result of blood pressure fall and a rise in total cholesterol.
References1. Adachi H, Hino A. Trends in nutritional intake and serum cholesterol levels over 40 years in Tanushimaru, Japanese men. J Epidemiol 2005; 15: 85-9.
2. Liu L, Ikeda K, Yukio Yamori Y. Changes in Stroke Mortality Rates for 1950 to 1997. A Great Slowdown of Decline Trend in Japan. Stroke 2001; 32: 1745
3. Shimamoto T, et al. Trends for Coronary Heart Disease and Stroke and Their Risk Factors in Japan. Circulation. 1989; 3: 503-15.