High levels of an amino acid in the blood could be responsible for heart disease
the latest addition to the list of factors that lead to heart disease is one that depends on internal regulation of the body. Amino acids, the basic building blocks of proteins, are required by the body for metabolism. But a recent study conducted by Ottar Nygard and others in Haukeland University, Bergen, Norway, has found that high levels of an amino acid, homocysteine, may lead to heart disease ( New England Journal of Medicine , Vol 337, No 4).
The researchers studied 587 people with coronary artery disease at the Bergen University Hospital for five years. In this period, many of the patients underwent either bypass surgery or angioplasty, and 53 men and 11 women died. The researchers studied their health reports to understand the relationship between homocysteine levels and the risk of heart attack. According to the study, people with high levels of homocysteine had a risk of getting a heart attack four-and-half times greater than those with normal levels.
Homocysteine is generated from methionine, present in protein-rich foods, and helps in the manufacture of proteins and cell metabolism. However, high levels of this amino acid can lead to clumping of blood platelets. The clumps may accumulate, causing scars and thickening of blood vessels. This helps molecules of cholesterol to stick to blood vessel walls, which cause further thickening, proving fatal in the long run.
Unlike cholesterol, which can be regulated by drugs and diet control, patients with high levels of homocysteine only need to eat more vegetables and vitamins to regulate it. Although homocysteine is not the only agent that leads to heart disease, it certainly plays a key role in causing the disease, according to the researchers.
That homocysteine was involved in thickening of blood vessels was suspected almost 30 years ago. In 1969, Harvard physician Kilmer McCully studied the case of an eight-year-old who had died of a stroke. McCully was amazed to find that blood vessels in the boy's body were thick like an old man's and the blood had high levels of homocysteine. Studies showed the boy had some genetic defect that caused excessive production of the amino acid.
Though the exact cause of over-production of homocysteine is still not known, there is sufficient evidence to show that the problem lies in its non-conversion to a metabolically usable form. For instance, vitamins b 6, b 12 and folic acid work together in such a conversion. Deficiency of these vitamins could lead to accumulation of the amino acid in the blood.
A simple solution for people prone to accumulation of homocysteine is intake of protective vitamins. The Harvard Health Letter recommends greater consumption of a range of foods -- including green vegetables, beans, peas, whole-grain cereals, certain meats and dairy products. Doctors agree that instead of waiting for a drug which could be developed to solve the problem, it is better to resort to dietary changes.
However, some cardiologists do not agree that merely changing over to vitamin-rich foods would solve the problem. They even question the role of homocysteine in the thickening of blood vessels. According to Roger Blumenthal at the Johns Hopkins University, usa, other factors -- such as obesity, smoking and a poor diet -- are equally responsible for damaging the cardiovascular system. The number of cardiac cases attributable to homocysteine alone do not exceed 20 per cent, says Blumenthal.
Some experts are also of the opinion that high levels of amino acids cannot be reduced by merely eating vitamin-rich foods. It is well-known that a certain level of cholestrol is required and maintained by the body. When people eat less fat, the liver manufactures more cholesterol from other sources. The same thing can happen in case of homocysteine. So more studies are required to look into the relationship between homocysteine and cholesterol and their regulation by vitamins b 12, b 6 and folic acid.
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