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The Theme of Health in Properties of Matter

Density, Cholesterol, and Heart Disease

We've already learned how Archimedes used the density of solids and the water displacement method to distinguish between silver and gold, but did you know that the density of cholesterol in our bodies can mean the difference between life and death?

Cholesterol is a fatty substance found in many animal-products we consume such as beef, eggs, fish, poultry, and milk. Our bodies use cholesterol for several purposes. While we need cholesterol to maintain several bodily functions, excessive amounts of it in the blood can be deadly.

Cholesterol structure. (Image from here.)

Too much cholesterol can lead to deposition of the stuff in the walls of arteries. This can cause a condition called atherosclerosis, or blocking of the arteries. These blockages are dangerous because they reduce or stop blood flow to important organs such as the heart, lungs, and brain. When such a blockage occurs, the tissue is deprived of oxygen and this can cause serious damage or even death. Heart attacks are a result of the heart muscle being deprived of oxygen while strokes result when parts of the brain are deprived of oxygen. 10

Atherosclerosis diagram. (Image from here.)

The risk of stroke and heart attack increases with increasing blood cholesterol levels. Cholesterol is carried in the bloodstream by a class of substances known as lipoproteins. This is where density comes into play because lipoproteins are classified according to their density.

The main carriers of blood cholesterol are low-density lipoproteins, or LDLs. These are also known as "bad cholesterol" and have a density of 1.04 g/cm3. They are bad because they tend to deposit cholesterol on arterial walls, which we already learned can lead to blockages resulting in heart attacks and strokes.

Cholesterol is also carried by high-density lipoproteins, or HDLs. These are also known as "good cholesterol" and have a density of 1.13 g/cm3. HDLs transport cholesterol to the liver for processing and excretion. This means HDLs have a tendency to reduce cholesterol deposition on the arterial walls.

Too low a level of HDLs (below 35 mg/ 100mL) is considered a risk factor for heart disease. Exercise, along with a diet low in saturated fats, is believed to raise HDL levels in the blood while lowering LDL levels. Maintaining a healthy balance is the key to a happy healthy heart (and life).

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