Cholesterol is a lipid that can be both manufactured by the body and ingested in food. It should be noted that dietary cholesterol is not the same as cholesterol found in the blood (serum cholesterol) and that dietary cholesterol often has little impact on the levels of cholesterol in the blood.

Are high levels of cholesterol in the blood harmful? In short, yes, a number of studies have found a correlation between coronary heart disease and high levels of serum cholesterol.

The graph below shows the combined results of three Finnish studies from 1972, 1977 and 1982 for men aged between 30 and 59.

As you can see, those with serum cholesterol levels below 5mmol/L made up 10% of the population yet represented less than 3% of total coronary heart disease deaths. Those with serum cholesterol levels above 8mmol/L made up slightly more than 10% of the total population but accounted for over a quarter of coronary heart disease deaths.

The odds of dying from coronary heart disease were found to be almost five times greater for those with cholesterol levels above 8mmol/L compared to those with cholesterol levels below 5mmol/L.

In recent years a correlation has been found between the ratio of High Density Lipoprotein (HDL) and Low Density Lipoprotein (LDL) and heart disease. A high HDL/LDL ratio is associated with a reduced risk in heart disease. Because of this HDL has been nicknamed the “good” cholesterol” and LDL the “bad cholesterol”. Many scientists believe the ratio of HDL/LDL to be a better predictor of heart disease than total blood cholesterol levels.

It should be noted that HDL and LDL are not themselves cholesterol but actually act as transporters of cholesterol around the body. LDL transports cholesterol from the liver to the tissues where it is needed and HDL cholesterol transports cholesterol from the tissues to the liver where it is excreted as bile.

Scientists have speculated that a low ratio of HDL to LDL may cause heart disease because a lack of HDL carrying cholesterol away from tissues causes cholesterol to build up in the arterial walls leading to atherosclerosis (hardening of the arteries) and the formation of plaques.

LDL cholesterol levels can be lowered through reducing consumption of saturated and trans fats, exercising regularly, quitting smoking, consuming a diet rich in polyunsaturated fats and omega-3 fatty acids, eating large amounts of fibre, and consuming foods rich in antioxidants.