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RISK FACTORS FOR HEART ATTACK: LOW LEVELS OF HDL-HIGH LEVELS OF LDL—CHOLESTEROL

Research over the past ten years has presented us with a much clearer insight into the problems involved with blood fats. It is now established that the total cholesterol level as measured in most laboratories correlates very well with a substance which is called "low density lipoprotein". What does the term 'low density lipoprotein' mean? First, it is important to realize that blood fats or lipids cannot float freely in the blood circulation; the lipids are bound to protein; therefore, they are termed lipoproteins. With a special instrument, it is possible to measure these lipoproteins in their degree of density. Everyone has high density lipoproteins (abbreviated HDL) and low density lipoproteins (abbreviated LDL). Interestingly, HDL contains almost 50% protein and less than a quarter cholesterol, while LDL contains close to 50% cholesterol and less than a quarter of protein. From long-term observations it became quite clear that HDL levels, the higher they are, the more protective they seem to be from atheroscleortic heart disease. This is not surprising if one looks at all the factors, presently known to increase HDL levels. The only disturbing observation is that pesticides, too, and estrogen therapy after menopause may increase HDL levels (and we are not sure at this time whether this is cause for concern). On the other hand, elevated LDL levels are found in individuals who are, from many aspects, at higher risk—but who could do something about most of the factors listed in the second table.

As the HDL table indicates, only race and sex obviously cannot be influenced, but all the things we ought to do are listed on the left side: preference of vegetable oils and margarine over butter and other animal fats, regular exercise, abstaining from smoking, using alcohol in moderation, keeping the weight normal, remaining at normal cholesterol, triglyceride and blood sugar levels. For the first time in the past 30 years of research in risk factors, a unifying concept has emerged which gives us the assurance that it is worthwhile to intervene if we have one or several risk factors. At the same time, the multifactorial aspect of this disease becomes so obvious that it would be foolish to expect any major impact on the primary or secondary prevention of coronary heart disease if one would attempt to influence only one single risk factor.

The LDL table contains the gravest of all risk factors, hypercholesterolemia of the familial type, previously termed primary or essential or familial hypercholesterolemia, because it is running in families and has frequently wjped out entire generations even in adolescence. The survivors have carried the abnormal gene on to the next generation before succumbing to a heart attack usually in their thirties or forties. But the LDL levels are also elevated among smokers, inactive persons on a diet high in animal fat and more often seen in men than in women. Recently it was demonstrated that quitting smoking, taking up regular physical exercise and consuming a diet rich in vegetable oil, fish and skim milk products can definitely lower these LDL levels, thus contributing to a decrease in the overall risk for ischemic heart disease.

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