What is cholesterol?

Cholesterol is a type of lipid (fat), manufactured by the liver from the fatty foods that we eat and found in the membranes of cells. Cholesterol is insoluble in blood, so it is transported in the circulatory system within lipoproteins. There are five major groups of lipoproteins (Chylomicrons, Very Low- (VLDL), Intermediate- (IDL), Low- (LDL), and High-density lipoproteins (HDL)) which enable fats and cholesterol to move within the water-based solution of the bloodstream, transporting dietary lipids from the intestines to other locations in the body.

What is the difference between HDL and LDL?

People talk about LDL being ‘bad’ cholesterol and HDL being ‘good’ cholesterol. What they actually mean is that when cholesterol attaches itself to high-density lipoproteins it can then be transported away from your arteries to the liver to be eliminated—which is the main reason why HDL-bound cholesterol or HDL-C is sometimes called ”good cholesterol”, and why a high level of ‘good’ HDL is thought to be good for your heart.

Cholesterol that attaches to low-density lipoprotein (LDL-C) takes cholesterol from your liver to the body tissues. If there’s a high level of cholesterol in the blood it can build up in the walls of your blood vessels, causing them to narrow. To keep your heart healthy it’s important that your ‘bad’ cholesterol transporters (LDL) levels remains low and your ‘good’ cholesterol transporters (HDL) stays high.

How can you increase HDL levels?

There are a number of factors that can contribute to a high cholesterol level, such as a family history, getting older, being overweight, an under active thyroid gland, diabetes or kidney problems. The most common cause is eating too much saturated fat. Whilst there are a lot of dietary products on the market designed to help control your cholesterol level, recent research that suggests that endurance exercise training may help increase HDL-C levels.

Atherosclerosis is a condition in which an artery wall thickens as the result of a build-up of fatty materials such as cholesterol. When cholesterol is attached to High density Lipoproteins to become HDL-C there is an inverse correlation with the incidence of coronary artery disease, meaning that as HDL-C levels increase the occurrence of coronary artery disease decreases. HDL-C and in particular HDLC-2 have been shown to have a protective effect against atherosclerosis.

The benefit of HDL is due to the role HDL has in the removal of excess cholesterol from peripheral cells to the liver for excretion as bile. This process is known as reverse cholesterol transport (RCT). Acute exercise, exercise training and fitness can favourably affect the several key steps in RCT.

ABCA1 is a protein that also plays an important role in transporting cholesterol. Research involving ABCA1 deficient humans and mice has shown that ABCA1that has a significant role in plasma HDL-C levels and over expression of ABCA1 can favourably decrease the risk of atherosclerosis.

A study out this month in European Journal of Applied Physiology investigated plasma HDL-C levels and the expression ABCA1 in response to treadmill running training in rats. The rats were trained for 12 weeks, 5 days a week for 60mins a day.

The researchers from Iran found that the expression of the ABCA1 protein in the liver and intestine was significantly higher in trained animals compared to the control group. Previous research in rats has also shown that 6 weeks of moderate endurance training leads to ABCA1 expression in liver.

The paper’s author Behzad Khabazian also reported increased levels of plasma HDL-C and HDL2-C concentrations in trained rats following treadmill training. This was suggested to be due to the effect exercise had in inducing higher blood concentrations of other key elements involved in RCT and HDL-C metabolism.

So there you are, further evidence suggesting that exercise can help protect against heart and coronary artery diseases and more reasons to take up some form of endurance exercise.