Blood Cholesterol (HDL, LDL, & Triglycerides)

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Cholesterol will not mix with water, and therefore, needs some assistance to travelthroughout the blood stream. With the help of a form of cholesterol HDL (highdensity lipoprotein), packets of cholesterol are formed to help move cholesterolthrough the blood. HDL helps remove cholesterol from the body by transporting itto the liver. Another form of cholesterol is LDL (low density lipoprotein). LDL doesnot aid in the transportation of cholesterol out of the body, instead it depositscholesterol onto the vessel wall. LDL molecules contain much more cholesterolthan HDL molecules.

How to Increase HDL(Good Guys)

Exercise1. Cessation of smoking2. Weight reduction3.

How to Decrease LDL(Bad Guys)

Decrease saturated fat intake1. Maintain good body composition2. Increase dietary fiber3. Increase aerobic exercise4.

The total cholesterol/HDL ratio is more indicative of cardiovascular disease thanTC (total cholesterol). The amount of HDL and LDL in the blood are addedtogether, this number for all practical purposes, indicates the amount of totalcholesterol. Therefore, if your HDL count is low, the LDL count will account for theremainder of the total. For men an acceptable ratio of TC/HDL is 4.5 or below, andwomen is 4.0 or below.

Ratio of total Cholesterol toHDLRisk Men Women

Very low (1/2average) 11

Triglycerides(mg/dl)

< 130 Desirable< 150 Normal

150-199 Borderline200-499 High>= 500 Very High

Ratio of LDL to HDL

Risk Men WomenVery low (1/2

average) 1 1.5

Average risk 3.6 3.2Moderate risk(2x average) 6.3 5.0

High risk (3xrisk) 8 6.1

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HDL levels have an inverse relationship with coronary heart disease. The ability ofHDL to predict the development of coronary atherosclerosis has been estimatedto be four times greater than LDL and eight times greater than TC. Treatment isrecommended for those with an HDL level below 40 mg/dL. An HDL of 60 mg/dLis considered protection against heart disease.

New MNR imaging tests assess the size of LDL particles. Small LDL particles areassociated with a higher risk of cardiovascular disease.

Triglycerides

Elevated triglycerides in the blood increase the risk of heart disease. Triglyceridesdo not come directly from dietary fats. Instead, they are produced in the liver fromany excess carbohydrates that have not been used for energy.

NCEP Blood Lipid Guidelines

Adults 20 years and older should undergo cholesterol screening (total cholesterol,LDL cholesterol, HDL cholesterol, and triglycerides) every 5 years. Blood samplesshould be obtained after fasting.

LDL Cholesterol(mg/dl)

190 Very High

Total Cholesterol(mg/dl)

=240 High risk

HDLCholesterol

(mg/dl)

60 High(desirable)

Triglycerides(mg/dl)

500 Very High

The National Cholesterol Education Program (May 16, 2001), Journal of theAmerican Medical Association

Blood Lipid Transport

After consuming a meal containing fat, the bloodundergoes a transient increase in lipids, particularlytriacylglycerols, lasting several hours. This is knownas postprandial lipemia. Individuals consuming atypical Western diet spend approximately 18 hoursper day in this state.

Exogenous fat transport begins in the intestinewhere dietary fats are packaged into lipoproteinparticles called chylomicrons. Chylomicrons enterthe bloodstream and deliver their triglyceride toadipose tissue and muscle. The remnant ofchylomicrons is removed from the circulation by theliver.

Endogenous fat transportation begins when the liver secretes a Very Low DensityLipoprotein particle (VLDL). When a VLDL particle reaches the capillary of muscleor adipose tissue, its triglyceride is extracted, leaving an Intermediate DensityLipoprotein (IDL). Half of the IDL particles are removed from circulation by the

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liver within two to six hours of their formation. The remaining IDL transforms intoLow Density Lipoproteins (LDL) which circulate for approximately two and a halfdays before binding to LDL receptors in the liver and other tissues.

Small dense low density lipoprotein (LDL) are more atherogenic that larger LDLparticles because they are

more easily enter the vessel wallmore prone to oxidative modificationbind more tightly to the arterial wallcleared more slowly

The composition of triglyceride-rich lipoproteins (TRLs) are metabolically linked toLDL. LDL particle size is primarily affected by the plasma TG levels. Postprandialhyperlipidemia is associated with an increase in the proportion of small, denseLDL. Furthermore, prolonged lipemia promotes the transfer of core lipids betweenTRLs and high density lipoprotein (HDL) leading to a reduction in HDL cholesterollevels. This combination is known as the lipid triad or atherogenic lipoproteinprofile:

high plasma TG concentrationsincreased small dense LDLlow HD

Bravo E, Napolitano M, and Botham KM (2010). Postprandial Lipid Metabolism:The Missing Link Between Life-Style Habits and the Increasing Incidence ofMetabolic Diseases in Western Countries? The Open Translational MedicineJournal, 2010, 2, 1-13

Cholesterol Regulation

Elevated circulating cholesterol reduces the cells ability to make its owncholesterol by turning off the production of HMG CoA reductase, which interruptsa step in the biosynthetic pathway of cholesterol. Incoming LDL derivedcholesterol promotes the storage of cholesterol in the cell by activating ACATwhich reattaches a fatty acid to excess cholesterol molecules. This results incholesterol esters that are deposited in storage droplets. The accumulation ofcholesterol within the cell drives a feedback mechanism which stops the cellssynthesis of new LDL receptors. The cell adjusts its receptors, so only enoughcholesterol is brought in to supply its needs.

With Familial Hypercholesterolemia, an inherited mutant gene causes theabsence of LDL receptors. High circulating levels of LDL are found to be causedby an increased production and a decrease in the removal of LDL. Consequently,Familial Hypercholesterolemia leads to high blood cholesterol and heart attacks inthe young.

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