Micronutrients

Micronutrients

•  Organic – vitamins

-          Fat soluble vitamins (A, D, E, K)

-          Water soluble vitamins (B complex, C)

• Inorganic – minerals

-          Macrominerals

       Calcium, Phosphorus, Magnesium, Sodium, Chloride, Potassium

-          Micro/trace minerals

        Iron, Zinc, Iodine, Fluorine, Selenium, Copper, Chromium, Manganese, Molybdenum

Why micronutrients become deficient?

•  Low intake

-          Due to diseases

-          Due to age

-          Due to poverty

-          Due to alcoholism

•  Losses during cooking

• Low absorption / Metabolism

·         Due to diseases

·         Due to drugs

·         Due to alcohol

·         Due to age

•  Increase requirements

·         Due to infancy

·         Due to adolescence

·         Due to pregnancy

·         Due to lactation

•  Increase blood loss

·         Due to diseases

·         Due to Parasites

·         0.5 mg blood/day lost due to menstruation

Micronutrient deficiencies

Arises due to:

• Inadequate intake

·         Malnutrition, food faddism

·         Malabsorption

·         Alcoholism

•  Consequences of disease

• Consequence of therapy

·         Dialysis, Total Parenteral Nutrition (TPN)

Vitamins

History of vitamins

Casimir Funk, a Polish biochemist, isolated an antineuritc (antiberiberi) substance from rice bran

Named it “vitamine”

Contains an amine group

Vital for life

Definition of a micronutrient

A substance, such as a vitamin or mineral, that is essential in minute amounts for the proper growth and metabolism of living organisms.

What are vitamins?

Essential organic compounds

Some are not dietary essentials

   Vitamin D

   Niacin containing coenzymes are derived from tryptophan

Needs in very small amounts (micronutrients)

Involved in fundamental functions of the body

Not related chemically

Not only amines so “e” was dropped

Not metabolic fuels (like glucose or fatty acids) or structural nutrients (like amino acids)

           Regulators (catalysts) of reactions

           Some are involved in,

           Growth

           Energy metabolism i.e. act as co-enzymes

           Cellular integrity (e.g. antioxidants)

Vitamins are classified according to solubility in water or organic solvents. Solubility affects the properties of the vitamins.

	Water Soluble	Fat Soluble
Absorption	Passive or active diffusion B12 needs intrinsic factor and R protein	Require bile salts Incorporated into micelles, passive diffusion
Transport	Portal vein to liver	Lymphatic systems to liver
Storage	Not stored in appreciable amounts except for B12	Stored in adipose tissue, except for vitamin K
Excretion	Excess excreted in urine when renal threshold exceeds	Minimal, a little lost in bile
Toxicity	Only at mega doses	At relatively low doses, dangerous/fatal except for vitamin K
Deficiency symptoms	Develop rapidly, overlapping symptoms	Slow to develop, except in children
Requirements	Except for vitamin C, required by most simple and complex organisms on a daily basis	Required only by complex organisms. Not required on a daily basis

Vitamins

Fat soluble vitamins

Vitamin K (phylloquinone)

Vitamin A (retinol)

Vitamin D (calcitriol)

Vitamin E (tocopherols)

Water soluble vitamins

Vitamin B complex

Divide according to the function

Energy releasing

Thiamin (B₁)

Riboflavin (B₂)

Niacin (B₃)

Biotin

Pantothenic acid (B₅)

Haematopoietic – Synthesis of blood

Folic acid

Vitamin B₁₂ (cobalamin)

Other

Vitamin B₆ (pyridoxine)

Vitamin C (ascorbic acid)

Fat – soluble vitamins

Structurally related compounds with different biological activity

·         Vitamin A – All trans retinol, retinal, retinoic acid

                      Light sensitive chromophore

                      Hormone like activity

·         Vitamin D – Cholecalciferol (vitamin D₃)

                      Precursor of a hormone

·         Vitamin E – Tocopherols

                     Membrane bound antioxidant

·         Vitamin K – Phylloquinone: K1,

                     Precursor of a coenzyme

·         Absorption requires adequate dietary fat (10%) and bile

·         In defective fat absorption deficiency is likely

·         Fat malabsorption syndromes – alcohol abuse, intestinal diseases, cystic fibrosis, celiac disease, crohn’s disease

Vitamin D

·         Vitamin D₃ – cholecalciferol

·         Vitamin D₂ – ergocalciferol – present in plant

·         Vitamin D₃ can be synthesized in the body

Most of the requirement met by endogenous synthesis

Dietary sources

·         Vitamin D₃ : Animal foods – liver, egg yolk, butter, fortified milk/margarine

·         Provitamin D₂ – fungi and yeasts

Cholecalciferol converts to 25-hydroxycholecalciferol by 25-hydroxylase enzyme. 25-hydroxycholecalciferol converts to 1,25-dihydroxycholecalciferol (calcitriol) by 1 alpha – hydroxylase enzyme.

1, 25 – dihydroxycholecalciferol (calcitriol) is the active form. It maintains calcium homeostasis. It affects the calcium and phosphate absorption from the intestine. It is essential for bone mineralisation and resorption. It is important for calcium and phosphate resorption from kidney.

Functions of vitamin D

Function as a hormone

·         Main function – Ca absorption and homeostasis

Maintains adequate plasma levels of calcium

When necessary, calcitriol can:

·         Increase uptake of calcium by the intestine: by increasing the gene expression of calcium binding proteins

·         Minimize loss of calcium by the kidney

·         Stimulate bone resorption

Synthesis and secretion of parathyroid and thyroid hormone

Acts like a steroid hormone – binds to nuclear receptor protein

 

1,25 – dihydroxycholecalciferol enter into the intestinal cell, then enter into the nuclear, then binds to intra-nuclear receptors, and then activate specific genes, then that gene produce Ca²⁺ binding proteins.

Other functions of Vitamin D

·         Controls cell differentiation

·         Affects the immune system sp. Cell-Mediated Immunity (CMI)

·         In large doses suppresses certain aspects of immunity

Rx of autoimmune diseases

·         Type 1 diabetes

·         Systemic lupus erythematosus (SLE)

·         Rheumatoid arthritis

Vitamin D & health in the 21^st century: bone & beyond. Am J Clin Nutr 80(6): Dec. 2004

  

Causes of deficiency

·         Inadequate dietary intake

·         Increased requirement

·         Inadequate exposure to sunlight

·         Steatorrhoea

·         Long term treatment with antiepileptics (phenytoin) or sedatives (phenobarbital)

Vitamin D status – plasma 25-hydroxy D3

  

Factors influencing the synthesis in the skin

·         Season, latitude, time of day and degree of exposure of skin

·         Solar radiation responsible for causing wrinkles & skin cancer (in genetically susceptible people) is the same radiation for producing vitamin D

·         Advise people, specially elderly that exposure to morning or late afternoon for vitamin D synthesis and less damaging to skin

Requirements

1 micro gram = 40 IU

·         Adults            2.5 microgram (100 IU)

·         Children         5    microgram (200 IU)

·         Pregnant women   10 microgram (400 IU)

·         Lactating women   10 microgram (400 IU)

Hypervitaminosis D

5 x RDA is toxic, leads to hypercalcaemia

Deposition of Ca in lungs, kidneys

Vitamin D deficiency

·         Rickets

·         Maternal vitamin D deficiency during pregnancy:

-          Linked to maternal osteomalacia

-          Neonatal hypocalcaemia & tetany

·         Placental transfer of vitamin D to fetus   important because of low vitamin D content in human milk (vary from 0.3 – 0.9 microgram/L)

·         Vitamin D and Ca protect against osteoporosis