WHAT most of us are not aware of is that 80% of cholesterol is derived from the liver and 20% from our diet.
“Cholesterol from food doesn’t contribute significantly to the elevation of cholesterol in the blood,” said Associate Prof Dr Hapizah Mohd Nawawi, the consultant chemical pathologist and head of the Chemical Pathology Unit at Universiti Kebangsaan Malaysia, who presented a talk on Cholesterol Diet and Coronary Heart Disease in Raub, Pahang recently, in conjunction with the presentation of the Raub Heart Study to the public there.
“It does play a role but not as much as from a high-fat diet, particularly saturated fat. The message to put across is that you can have food that is cholesterol-free, but it might also be high in saturated fat. High content of saturated fat will enhance the intra-cellular synthesis of cholesterol.”
Examples of saturated fat are animal-derived food such as red meat, egg yolk and seafood such as crab and prawns. Internal organ-derived food like liver and kidneys are also high in saturated fat.
As is already well-known, not all cholesterol is bad. The two main types of cholesterol are the LDL (low-density lipoprotein)-cholesterol and the HDL (high-density lipoprotein)-cholesterol. The LDL, or bad cholesterol, forms deposits in the inner lining of blood vessels. The major function of the HDL, the good cholesterol, is transporting cholesterol from the peripheral organs as well as the blood back to the liver. So, if you have a higher level of HDL, the better it is for you. And the higher the level of LDL, the higher the risk of coronary heart disease.
“There is also triglyceride, another component of fat which remains in the stock fat,” explained Hapizah. “Now, there is increasing evidence that triglycerides also play a role in coronary heart disease typically in people with obesity or diabetes. What we see most often is that when the level of triglycerides is high, the level of good cholesterol is low. (And when obesity is decreased), the level of triglycerides come down, and the level of good cholesterol goes up.”
Hypercholesterolaemia, or the level of cholesterol in the blood, is the major risk factor of coronary heart disease but it is not the only factor.
“The definition of hypercholesterolaemia varies from individual to individual,” Hapizah elaborated. “What may be a high level of cholesterol in the blood for one person may not be so for another. For example, a person who is high risk, with established coronary artery disease, or who has had a bypass, or even a person who is diabetic may have a lower threshold of cholesterol. That’s a very important point to put across.”
Whether the level of cholesterol in an individual can be considered high depends on various factors, and the number of risk factors present in that individual. After that is determined, the individual can be categorised into either one of three categories – high, medium or low risk.
Age is also another risk factor. For males, the age of 45 and above is considered a risk factor. For females it is 55 and above.
Another factor is family history of premature heart disease, which is below 55 years of age for males and 65 for females. Other risk factors include smoking and hypertension, whether treated or not. – By Allan Koay