About Dietary Reference Intake (DRI)

 

 

The Dietary Reference Intake can be defined  a system of nutrition recommendations that estimates the amounts of nutrients required to prevent deficiencies and maintain optimal Health.

 

The DRI includes some concepts that sometimes are used as equivalents, when they are not. In other cases, the same concept receive different names, depending of the source of the article you are reading.

DRIs consists of four dietary reference standards:

 

1.- Estimated Average Requirement (EAR): Average daily nutrient intake level estimated to meet the requirement of one half of the healthy individuals in a specific age and gender group.

 

 2.- Recommended Dietary Allowance (RDA): Average daily Dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97-98%) individuals (EAR+2DS) on each life state and gender group. It is approximately 20 % higher than the EAR. RDA are printed in food labels in the United States and Canada.  (The definition of RDA is similar to the definition of  Recommended Nutrient Intake (RNI)  used by the World Health Organization and other international organizations).

 

 3.- Adequate Intake (AI): Estimation of nutrient intake in healthy people (used when EAR and RDA are not known)

 

 4.- Tolerable Upper Intake Level (UL): Highest average daily intake level from food, water and supplements that is likely to pose no risk of adverse health effect from excess in almost all apparently healthy individuals in an age and gender specific population group. (This concept is important mainly in relation to nutritional supplements, since the ingestion of natural foods is regulated in the body through mechanisms of absorption and excretion), In absence of observations of known adverse effects, it is used a default value of 10 times de Recommended Dietary Allowance.

 

More information about these reference standards can be found at:

 

Dietary Reference Intake

Reference dialy Intake 

 Interactive DRI for health care professionals

 Yates, A.A.: Dietary Reference Intakes –What is new and how to use them (Power point presentation)

Who Experts Committee:

Vitamin and Mineral requirements in human nutrition

World Health Organization, 2004

About Tea and Toasts

 

A 70 year-old English lady that lives alone is admitted to the hospital for evaluation of a leg wound that is not healing properly. The patient also complains of pain in muscle and bones. On the examination, you find some hemorrhagic lesions in the skin, including ecchymosis in buttocks and both legs and petechiaes in other areas of the skin. The nails show splinter hemorrhages. When asked about her dietetic habits, the patient refers that she is too old to eat so much, so she has a very frugal lunch and dinners based mainly in tea and toasts.

Laboratory examinations show normal blood coagulation tests and Hemoglobin of 9.8 g/dL

 

The treatment for the condition described above should consist mainly in the administration of the following vitamin:

 

a)     Ascorbic Acid

b)     Biotin

c)      Folic Acid

d)     Pantothenic acid

e)     Niacin

f)       Vitamin B1

g)     Vitamin B2

h)    Vitamin B6

i)       Vitamin B12

j)       Vitamin D

k)     Vitamin E

l)       Vitamin K

Biochemistry of platelets (II): Platelet receptors.

 

Platelet aggregates

 

Platelet membrane is rich in glycoproteins organized as receptors of very different types: tyrosine kinase receptors, integrin family receptors, receptors rich in Leucine (LRR), protein G linked transmembrane receptors, immunoglobulin super family proteins, lectins and others.

 

Many of these receptors play an important role in the haemostatic function of platelets, participating in the interaction among platelets, between platelets and vascular tissue, and among platelets and coagulation factors and other agonists (ADP, epinephrine, thromboxane A2, and others)

 

Other platelet membrane receptors are involved in the participation of platelets in processes such as inflammation, tumor growth, metastasis and immunologic type reactions.

 

From the medical point of view, GPIIb-IIIa and GPIb receptors are particularly important.

 

[GP] IIb-IIIa is the most abundant receptor in the platelet surface, representing almost 15 % of all the proteins in the cell surface. This receptor is a member of the Integrin receptors family and is also called Integrin αIIb-β₃. This is an important receptor in platelet aggregation, since it binds Von Willebrand factor and fibrinogen.  The relevance of this kind of receptors for an appropriate hemostasis is obvious if we consider that genetic mutations which provoke the absence or formation of lesser quantities of these receptors give rise to platelets that are not able of binding to fibrinogen and aggregate (Glanzmann Thromboasthenia).

Another important medical issue related to these receptors is the fact that nowadays antagonists of these receptors have been developed for inhibiting platelet aggregation, so we can use anticoagulant drugs that inhibit platelet aggregation regardless of the agonist. Examples of these drugs are Abciximab: a human monoclonal antibody, Eptifibatide, a cyclic hexapeptide derived from the venom of a snake) and Tirofiban, a synthetic non-peptide molecule.

 

GPI-b (GPIb-GPIX-GPV) is a Leucine Rich Receptor (LRR) formed by a multiprotein complex of 4 different types of glycoproteins: GPIb alfa and GPIb beta, (linked through disulfide bonds) and GPIX and GPV (associated by non covalent forces).

 

This receptor is crucial for the platelets initial attachment to the extracellular matrix of the damaged vessel. This attachment is made through the Von Willebrand factor, which acts as a bridge between the sub endothelial collagen (exposed as a consequence of the vessel damage) and the GPI-b receptors in the platelet membrane.

 

The Bernard-Soulier syndrome is an autosomal recessive disorder which appears as a consequence of an absence or decrease of the glycoproteins that form the GPIb-GPIX-GPV receptors.

 

Excellent reviews on these issues can be found at the following links:

 

Platelet function defects.

 

Platelet function disorders 

 

Platelet receptors and signaling in the dynamics of thrombus formation

 

 Inherited Disorders of Platelets 

 

 Blood coagulation 

 

 Thromboasthenia of Glanzmann and Naegeli 

 

 Giant Platelet Syndrome