High blood pressure linked to memory loss

Published in The Hindu on August 25, 2009

Blood pressure
Uncontrolled high blood pressure can cause memory loss in people over a period of time. — Photo: Wikimedia Commons

Studies done on a small number of people have shown that uncontrolled hypertension (high blood pressure) can cause memory loss in people over a period of time. A large-scale study involving nearly 20,000 people and published today in the journal Neurology, the medical journal of the American Academy of Neurology, has now firmly established this.

The study, which involved people of age 45 and older, found that high diastolic blood pressure was more likely to cause cognitive impairment or problems with memory and thinking skills compared with people who had normal blood pressure. Diastolic blood pressure is the bottom number of a blood pressure reading. 120/80 is considered normal and a reading of 140/90 and above is considered as high blood pressure.

The study found that for every 10 point increase in diastolic blood pressure reading, the chances of a person having cognitive problems were 7 per cent higher. The results were valid after adjusting for factors such as age, smoking, exercise level, diabetes, and high cholesterol.

The study was undertaken in people who had participated in the Reasons for Geographic And Racial Differences in Stroke (REGARDS) Study. REGARDS was a large-scale population-based study undertaken across the U.S.

Hypertension can damage the arteries’ inner lining, which in turn leads to a chain of events that make the artery walls thick and stiff. It can also cause a build-up inside the vessels, thus making them narrow. The narrowing of the vessels, in turn, reduces the amount of blood that flows into the brain.

According to a paper published in 2005 in the journal Neurology, about one quart (1.14 litres) of blood flows through the brain every minute under normal conditions. Any reduction in this amount will not allow the brain to work efficiently.

Unlike the heart, the brain receives blood during both systole and diastole. “The brain is very sensitive to lack of oxygen. So any reduction in blood supply will lead to cognitive problems,” said Prof. K. Srinath Reddy, President of the Delhi based Public Health Foundation of India. “While high systolic pressure [the top number of a blood pressure reading] can cause stroke, heart attack, and kidney failure, high diastolic pressure [bottom number of a blood pressure reading] causes subtle damage like cognitive impairment.”

The biggest problem with hypertension is that it is asymptomatic, and many people are just not aware of their problem. According to the author of the paper, Georgios Tsivgoulis of the University of Alabama at Brimingham, cognitive impairment, which can be a precursor to dementia, can be easily prevented.

Prevalence in India

According to Prof. Reddy, the prevalence of high blood pressure in India is 24-30 per cent in urban areas and 12-14 per cent in rural areas. “Many population studies have shown that the awareness [of their status] is only 30 per cent in the urban population,” he said. “Of the 30 per cent [who are aware], only half have their BP adequately controlled.” It is far worse in the case of the rural population. “Awareness is only 10-12 per cent, and only 4-5 per cent of these people have their BP adequately controlled.”

The simplest preventive measure is to reduce the salt intake. Sodium in salt increases the contractility of the blood vessels. Increasing the intake of fruits and vegetables is yet another preventive strategy. “The potassium in fruits and vegetables counteracts the effects of sodium,” said Prof. Reddy.