Egg yolks ,cholesterol and

Vitamin A

Dr. Yousef Elshrek

• One of the dietary recommendations in the prevention of coronary heart disease is to limit egg consumption , because eggs have been shown to be a major source of dietary cholesterol

• Dietary cholesterol increases serum total and LDL-cholesterol concentrations , which are established risk factors for coronary heart disease

• Several epidemiologic studies found no relation between egg consumption and risk of coronary heart disease .

• The absence of such a relation may imply that the recommendation of lowering egg consumption is of little use in the prevention of coronary heart disease.

• One egg contains ≈200 mg/cholesterol.

• Although it is obvious that dietary cholesterol

increases total cholesterol concentrations .

• Several studies showed that dietary cholesterol

increases not only concentrations of LDL

cholesterol but also concentrations of HDL

cholesterol .

• Because HDL cholesterol may protect against

coronary heart disease, the adverse effects of

egg consumption on total and LDL-cholesterol

concentrations might be attenuated by the

favorable effects on HDL-cholesterol

concentrations.

• Weggemans et. al. 2001 . Found that , the addition of 100 mg

dietary cholesterol/d increased

• The ratio of total to HDL cholesterol by 0.020 units (95% CI:

0.010, 0.030),

• Total cholesterol concentrations by 0.056 mmol/L (2.2 mg/dL)

(95% CI: 0.046, 0.065 mmol/L; 1.8, 2.5 mg/dL),

• HDL-cholesterol concentrations by 0.008 mmol/L (0.3 mg/dL)

(95% CI: 0.005, 0.010 mmol/L; 0.2, 0.4 mg/dL).

• They concluded that dietary cholesterol raises the ratio of total

to HDL cholesterol and, therefore, adversely affects the

cholesterol profile.

• Their advice is to limit cholesterol intake by reducing

consumption of eggs and other cholesterol-rich foods may

therefore still be valid.

• People with this risk variant need to be

particularly careful about their total fat and

cholesterol consumption.

• This depend on type of gene

• If you carry the E4 variant of the APOE

gene (often referred to as APO-ε4 allele; CC

genotype rs429358).

• This variant is found in approximately 20%

of African Americans, 31% of Africans and

20% of people from Finland.

• Definitions of APOE

• APOE A gene on chromosome 19q13.2 that encodes apolipoprotein E, the main apoprotein of chylomicrons, which binds to a specific receptor on liver cells and peripheral cells. ApoE mediates binding, internalisation and catabolism of lipoprotein particles and serves as a ligand for the LDL (apo B/E) receptor.

• APOE mutations cause hyperlipoproteinaemia type III (familial dysbetalipoproteinaemia), which is characterized by increased plasma cholesterol and triglycerides due to impaired chylomicron and VLDL remnant clearance.

• A protein component of lipoprotein complexes found in very-low-density lipoprotein (VLDL), high-density lipoprotein, and chylomicron remnants

• It facilitates hepatic uptake of chylomicron and VLDL remnants and is elevated in patients with type III hyperlipoproteinemia.

• One form of apolipoprotein E has been linked to Alzheimer's disease

• Definition of

1. VLDL. : A plasma lipoprotein that is produced primarily by the liver with lesser amounts contributed by the intestine, that contains relatively large amounts of triglycerides compared to protein, and that leaves a residue of cholesterol in the tissues during the process of conversion to LDL — compare HDL.

2. Chylomicrons (a droplet of fat present in the blood or lymph after absorption from the small intestine).

• Chylomicron remnants (Metabolic products of chylomicron particles in which triglycerides have been selectively removed by the Lipoprotein lapase. These remnants carry dietary lipids in the blood and are cholesterol-rich. Their interactions with microphages; endothelaial cells ; and smooth muscle cells in the artery wall can lead to atherosclerosis)

• However, just because eggs contain cholesterol does not mean they are not a healthy food.

• Eggs, and specifically egg yolks, are one of the richest sources of retinol, the biologically active form of vitamin A.

• When your body does not have enough retinol, you may experience symptoms of vitamin A deficiency like:

1. Acne

2. Bumpy skin

3. Dry eye

4. Hair loss

5. Poor night vision

• There are two major

source of vitamin A in the

diet:

1. animal products, such

as eggs, milk, butter,

cheese and liver, which

provide retinol

2. Colorful fruits and

dark green vegetables,

which provide

carotenes.

3. Retinol is the active

form of vitamin A.

4. Carotenes must first be

converted to retinol to

be functional in the

body.

Fig. (1) Carotenes convert to retinol

• Certain genetic variants in the carotene

conversion enzyme (BAMO1) are associated

with an individual’s ability to convert carotenes

to retinol.

• 70% East Asians, 28% Europeans and 17%

Africans carry variants associated with lower

conversion, which means they can experience

vitamin A deficiency even when consuming

sufficient carotenes from fruits and vegetables.

• The preferred vitamin A source for people with

these variants is retinol from animal product

• However, more vitamin A not always better; too much vitamin A can be toxic to your body.

• Animal sources such as liver contain very high amounts of vitamin A, and portions should be carefully planned.

• To benefit from vitamin A while still avoiding toxicity, the best practice is to monitor how much vitamin A you get from your diet and/or supplements.

• The recommended daily value by the Dietary Guidelines is 700 mcg for females and 900 mcg for males.

• The upper limit is 3,000 mcg.