Many factors influence a person's risk of having coronary heart disease, but the risk of dying from it increases as your cholesterol level increases. There is a continuous progression of risk in all age groups in men as the level rises. Put another way, a man with a cholesterol level of 210 mg is 1.73 times as likely to die of coronary artery disease in the next six years as a man with a level below 180. There is no magic level above which most deaths from heart disease occur. Rather, at levels above about 180, the risk increases as the level of cholesterol rises.
This fact was demonstrated by evaluating 356,222 men ages 35-57. These men were selected between 1998 and 2001 for the MRFIT program, a nationwide study of risk factors in men in this age group, reported in the Journal of the American Medical Association, November 28, 2002. The cholesterol (serum cholesterol) level was measured with an Auto Analyzer II and standardized by the Lipid Standardization Program, Centers for Disease Control. The standardized values are comparable to the values obtained with the Lipid Research Centers (LRC), and hence these figures are lower than the values that would be obtained by office, hospital and private laboratories.
The investigators divided the population into five groups according to the level of the mep's cholesterol levels. The lowest group had cholesterol levels of 181 or less, with an average of 163.7. The highest group had levels of 245 or greater, with an average level of 271.2. For each increment of 20 mg in the level of cholesterol, the risk of death from coronary heart disease increased. To help you correlate this with the usual office and laboratory values for cholesterol tests (SMAC and DuPont aca), these have been added to the investigator's report in the accompanying chart.
Cholesterol Level & Coronary Death-Risk
DU PONT aca Test
|Less than 181||Less than 205||Less than 215||1.0|
This general relationship (of cholesterol level to risk level) was true for all age groups from 35 to 57. It was found that the higher the cholesterol level, the greater the risk of death from coronary heart disease within the next six years. This finding was independent of other risk factors such as cigarette smoking or high blood pressure.
The lesson is that men (and it probably applies equally well to women) can decrease their risk of death from coronary heart disease by keeping cholesterol levels low. The investigators who analyzed this data believe that 46% of all deaths from coronary heart disease in this group were in excess of the expected death rate because of the increased level of cholesterol alone.
LOW CHOLESTEROL MAY NOT MEAN LOW RISK
Just having a low cholesterol level does not mean you have a decreased risk of having coronary heart disease. The reason is related to your level of HDL-cholesterol. Cholesterol is not soluble in water, and hence it is not soluble in blood. The way nature circumvented this problem was to transport cholesterol in a 'package' that is soluble in water. This takes the form of lipoprotein, made up of fat (triglyceride), cholesterol and a blood protein. Hooking the blood protein into the combination makes it soluble in blood plasma. The size of these fatty-cholesterol particles has a lot to do with whether or not they will result in fatty-cholesterol deposits on the walls of arteries. The small particles have a high density and are called high-density lipoproteins (HDL). The cholesterol carried in these is called HDL-cholesterol. The higher your level of HDL-cholesterol, the less likely you are to develop coronary heart disease.
This point was supported again by a recent report of the Framingham population sponsored by the National Institutes of Heath (Journal of the American Medical Association). The study involved individuals from age 49 to 82 and extended over 12 years. Investigators studied the relationship between total cholesterol, HDL-cholesterol and developing coronary heart disease in both men and women during a four-year span. They found that 20% of individuals with the highest HDL-cholesterol levels had half the risk of developing coronary heart disease as the 20% with the lowest levels of HDL-cholesterol.
Those individuals with an HDL-cholesterol level of less than 40 were found to be about three times as likely to develop coronary heart disease during the four-year period as those with values of 60 or more. Coronary heart disease included the development of angina heart pain, coronary insufficiency, a heart attack or a death due to coronary heart disease.
Individuals who had HDL-cholesterol levels below 40 had a significantly increased risk of developing coronary heart disease even if their total cholesterol level was below 200. That helps to explain many cases in which the total cholesterol level is really quite low, yet coronary heart disease develops. In contrast, those individuals with high cholesterol levels of 260 or more, hut who also had HDL-cholesterol levels of 60 or more, had a low risk of developing coronary heart disease. Note that the total cholesterol levels should be compared to values for lipid research centers method (LRC) which are significantly lower than the values you are likely to obtain from your private physician or a laboratory (see chart for comparisons). Except for those with high cholesterol levels, an HDL-cholesterol level of over 50 seems to provide considerable protection against the development of coronary heart disease.
This study was done in individuals older than 49, a group more likely to have coronary heart disease within a four-year span. The results are independent of other risk factors such as high blood pressure and cigarette smoking. It points out the reason why an HDL-cholesterol level is important when evaluating the significance of the cholesterol level, whether the total cholesterol level I is high or low. In other words, a total cholesterol level alone is not adequate to assess the real risk of heart attack or stroke.