Cholesterol is an organic chemical substance present naturally in our body. It is an essential structural component of our cell membranes and is required for their proper functioning because it regulates membrane permeability and fluidity. Cholesterol is also an important component of the hormonal systems of the body and is involved in the manufacture of bile acids, steroid hormones, and vitamin D.
As cholesterol is very vital for our body, it is synthesized by our body in the liver.
Cholesterol is usually associated with fatty foods but the fact is that most cholesterol is made by our own bodies.
- The liver produces 75% of the cholesterol that circulates in our blood. The other 25% comes from food.
- For an average person of about 68 kg (150 pounds), the body synthesises about 1 g (1,000 mg) per day, and total body cholesterol is about 35 g, primarily located within the membranes of all body cells.
At normal cholesterol levels of 200 or less, cholesterol plays an important role in helping cells do their jobs. However, high cholesterol levels (hyperlipidemia) put us at risk of developing cardiovascular diseases.
Cholesterol provides both structure and function to our body.
- Cholesterol is required to build and maintain membranes; it modulates membrane permeability and fluidity.
- Compact layers of cholesterol-rich cell membranes (of Schwann cells) form myelin sheath which surround nerve fibers and provide insulation for efficient conduction of nerve impulses.
- Cholesterol is converted in the liver to bile which is then stored in the gallbladder. Bile contains bile salts, which solubilize/emulsify the water-insoluble fats in the digestive tract and aid in the absorption of fat molecules, as well as the fat-soluble vitamins A, D, E, and K.
- Cholesterol is involved in the synthesis of vitamin D and the steroid hormones, including the adrenal gland hormones (adrenocortisol and aldosterone), as well as the sex hormones progesterone, estrogens, and testosterone.
Lipoproteins – The Transporters of Cholesterol
Cholesterol is only slightly soluble in water so it is insoluble in blood. Therefore it is transported by lipoproteins – chemicals made up of lipids and proteins.
Lipoproteins are classified according to their densities. The more lipid and less protein a lipoprotein has, the less dense it is. Types of lipoproteins present in blood are:
- Very-low-density lipoprotein (VLDL),
- Intermediate-density lipoprotein (IDL),
- Low-density lipoprotein (LDL), and
- High-density lipoprotein (HDL).
Types of Cholesterol That Circulate In Our Blood
- Most of the cholesterol in the blood is carried by proteins called low density lipoproteins or LDL.
- LDL cholesterol is carried to the body’s cells, where the cells take as much cholesterol as they need, leaving the excess in the blood. If there’s constantly too much bad cholesterol left in the blood it can aid formation of plaque and thrombus in the arteries, which eventually cause blockages or break away to form clots and block other blood vessels. This is why it’s often referred to as ‘bad’ cholesterol.
- Until recently it was thought that eating saturated fat raised cholesterol but some doubt has been cast on this.
- For most people an LDL score below 100 is healthy, but people with heart disease need to aim for even lower LDL score.
- [ed. I had to add this because it’s not entirely clear that LDL is bad at all. All cholesterol exists for a purpose and is not there to kill us. Rather the small dense LDL particles are sticky and clog arteries. We can get more of the small dense LDL from a high carb diet and a sedentary lifestyle, and unfortunately for some, this type of LDL can also be hereditary]
- Up to one third of blood cholesterol is carried by high-density lipoproteins or HDL.
- HDL cholesterol is extra cholesterol from the tissues that gets carried away from the arteries to the liver, where the body gets rid of it. This type is important for a healthy heart as it’s the cholesterol that’s eliminated from the body – hence the reason it’s sometimes referred to as ‘good’ cholesterol. HDL removes cholesterol and prevents it from building up inside the arteries.
- Thus higher levels of HDL cholesterol are better. People with lower HDL scores are more likely to develop heart disease.
- Until recently it was thought that “healthy fats”, such as omega-3 fats, olive oil helped boost HDL cholesterol, but now doubt has been cast on this assertion.
- The body converts excess calories, sugar, and alcohol into triglycerides.
- This is the type of fat that is carried in the blood and stored in fat cells throughout the body.
- Those who indulge in high-carb foods, and those who are physically inactive, overweight, smokers, or heavy drinkers tend to have high triglycerides levels.
- A triglyceride score of 150 or higher puts you at risk of metabolic syndrome, which is linked to heart disease and diabetes.
Cholesterol Ratio – Determine Your Health Risk
- The link between cholesterol levels and risk of heart disease is calculated by determining the cholesterol ratio.
- Doctors rely on cholesterol ratio which is obtained by dividing your total cholesterol by your HDL cholesterol. For example, a total score of 300 divided by an HDL score of 50 equals a cholesterol ratio of 6 to 1.
- Doctors recommend maintaining a ratio of 4 to 1 or lower. The smaller the ratio, the healthier you are.
- This ratio is useful in estimating your risk of developing heart disease. However it is not important in guiding treatment. Doctors take an overall look at total cholesterol, HDL & LDL to determine your treatment plan.
Enjoy Your Meals!
All foods containing animal fat contain cholesterol to varying extents. Major dietary sources of cholesterol include cheese, egg yolks, beef, pork, poultry, fish, and shrimp. Human milk also contains significant quantities of cholesterol because it is necessary for healthy growth of infants.
- Initially cholesterol-rich foods like eggs, shrimps and lobster were forbidden because they had cholesterol in them.
- But now research has shown that the cholesterol we eat has a small effect on blood cholesterol levels for most people so these foods are no longer completely forbidden. [ed. The body makes its own cholesterol, so cholesterol is obviously not a bad thing. Our bodies do not produce substances which are designed to give us heart attacks!]
- An exception is those who are “responders,” whose blood levels spike after eating eggs. They should avoid cholesterol rich foods.
- Daily cholesterol limits are 300 mg for healthy people and 200 mg for those at higher risk of heart disease. One egg has 186 mg of cholesterol. So enjoy your meals!
Measuring Cholesterol Levels
People over 20 years of age should have their cholesterol levels checked at least once every five years.
This is done with a simple blood test known as a fasting lipoprotein profile. It measures the different forms of cholesterol that are circulating in your blood. It is done after 9-12 hours of not eating anything – so that lipids and cholesterol from your latest meal does not interfere with the results.
Lipid profile is the collective term given to the estimation of total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and triglycerides. An extended lipid profile may include very low-density lipoprotein.
A blood sample after 12-hours of fasting is taken by a doctor, or a home cholesterol-monitoring device is used to determine a lipoprotein profile.
- Total cholesterol is defined as the sum of HDL, LDL, and VLDL.
- For economic reasons only the total cholesterol, HDL, and triglycerides are measured.
- VLDL is usually estimated as one-fifth of the triglycerides and the LDL is estimated using the Friedewald formula (or a variant): Estimated LDL = [Total cholesterol] – [Total HDL] – [Estimated VLDL].
- Direct LDL and VLDL are measured when triglycerides exceed 400 mg/dL because the estimated values of VLDL and LDL have more error when triglycerides are above 400 mg/dL.
A lipid profile may also be ordered at regular intervals to evaluate the success of lipid-lowering lifestyle changes such as diet and exercise, or to determine the effectiveness of drug therapy such as statins and fibrates.
When it comes to lowering cholesterol, it’s particularly important to lower LDL cholesterol as this is the type that increases the risk of heart disease, while maintaining or increasing levels of HDL cholesterol. This can usually be achieved through changing your eating habits, losing weight and exercising regularly. Our other article “High cholesterol” gives more information about this. It suggests methods on how to lower cholesterol levels and provides guidance on living a healthy life by combating high cholesterol levels.
What Should My Cholesterol Levels Be?
National Cholesterol Education Program, Adult Treatment Panels and The American Heart Association suggest the optimal levels of cholesterol.
- 4:1 or less
Total Cholesterol level
- Less than 200 is ideal.
- 200 – 239 is borderline high.
- Above 240 means you’re at increased risk of heart disease. Take immediate action!
LDL Cholesterol level
- Less than 100 is ideal for people who have heart disease or other diseases like diabetes, high blood pressure etc.
- 100 to 129 is normal for healthy people who do not have any accompanying cardiovascular disease.
- 130 to 159 is borderline high.
- 160 or more means you’re at a higher risk of heart disease. Take immediate action!
- LDL values for children should be less than 35 mg/dL.
- [ed. again what matters is the type of LDL you have. Don’t get all uptight if you have high LDL. You’ll need more research done to determine if the LDL is small and dense to know if you are sick]
HDL Cholesterol levels
- Less than 40 means you’re at higher risk of heart disease. Take immediate action!
- 60 or higher is optimal and it greatly reduces the risk of heart disease.
- Less than 150 mg/dL is best.
High Cholesterol Number is Bad – Just a Myth!
The concept that high cholesterol numbers are bad has been proven wrong. No doubt a total cholesterol reading can be used to assess an individual’s risk of heart disease, however, it should not be relied upon as the only indicator. The individual components that make up the total cholesterol reading (LDL, HDL, and VLDL) are very important in measuring risk.
For example, your total cholesterol may be high, but this may be due to very high good (HDL) cholesterol levels – which is good and can actually help prevent heart disease.
So, while a high total cholesterol level may indicate that there is a problem with cholesterol levels, the components that make up total cholesterol should also be measured for accurate diagnosis.
Top News Service CNN Educates Us About Cholesterol
(Click article for full size)
Research Studies Clarify Misconceptions Regarding Cholesterol Numbers
- “Total cholesterol was not associated with the risk of coronary heart disease.” (http://ukpmc.ac.uk/abstract/MED/193398/reload=0;jsessionid=DmRJXVC3QZ0y5yrewYFj.6)
- “Participants at the 80th percentile of HDL concentrations were found to have half the risk of CHD developing when compared with subjects at the 20th percentile of HDL concentrations.” (http://jama.jamanetwork.com/article.aspx?articleid=363237)
- “Serum triglyceride concentration has prognostic value (predicting outcome of illness or therapy), both for assessing coronary heart disease risk and in predicting the effect of drug treatment, especially when used in combination with HDL-C and LDL-C.” (http://circ.ahajournals.org/content/85/1/37.short)
- “Findings indicate that in older adults, 5 wks of consuming 1 egg per day did not elevate serum lipids and lipoprotein cholesterol concentrations.” (http://jn.nutrition.org/content/136/10/2519.short)
- “Triglycerides were associated with the incidence of coronary heart disease.” (http://ukpmc.ac.uk/abstract/MED/193398/reload=0;jsessionid=DmRJXVC3QZ0y5yrewYFj.6)