Introduction to Micronutrients Flashcards
Fat soluble vitamins
Vitamin A (retinol, retinal, retinoic acid)
Vitamin D (ergosterol, cholecalciferol)
Vitamin E (tocopherol, tocotrienol)
Vitamin K (phylloquinone, menaquinone)
Fat soluble vitamins generally hydrophobic- need to be carried by protein to get around the body
In some cases they’re hormones, retinoic acid is the hormonal form of vitamin A, calcitriol is hormonal form of vitamin D (secreted by kidneys)
Hormones are very tightly regulated with sophisticated feedback systems
Water soluble vitamins
Vitamin B group (important roles in lots of different bodily reactions particularly energy metabolism)
-thiamin, riboflavin, niacin, biotin, pantothenic acid, pyridoxine, folic acid, cobalamin (choline)
Vitamin C- Ascorbic acid and dehydroascorbic acid
Depend on substrates for production, retinoic acid depends on retinol or b-carotene
Early days difficult to separate out selenium deficiency and vitamin E as have similar effects
Key distinctive features but only when they get more serious
Problem is only when issues become severe can features be discerned and can tell what vit/mineral is responsible for deficiency
Minerals
Inorganic micronutrients
Elements in the periodic table (except C, H, O and N) which are essential components of the diet to maintain health
Just because you need less of something doesn’t mean it’s less important
Macrominerals
Calcium Ca2+ 15% bw- 95-98% located in skeleton Phosphorus PO4- 10% bw Potassium K+ 2% bw Sodium Na+ 1.6% bw Sulfur SO42- 1.5%bw Chlorine Cl- 1.1% bw Magnesium Mg2+ 0.4% bw
Macrominerals Electrolytes
Na -source- table salt, processed foods -function- muscle contraction, fluid, pH balance -deficiency- muscle cramps, coma Cl -source- table salt -function- as for Na, HCl -deficiency- as above K -source- fruits and veg, dairy, meats and cereals -function- as for Na -deficiency- heart failure, usually form excessive losses
Minerals functions
Bones and teeth -Ca, P, Mg Control of body fluid composition -Na, Cl, K, Mg, P Components of enzymes and other proteins -Fe, P, Cu, Zn, Mn, Co
Minerals Classification
Macrominerals
-Ca, P, S, K, Na, Cl, Mg
Trace elements
-Fe, Zn, Cu, Se, I, Mn, Cr, Co
Bioavailability of Minerals
The proportion of mineral ingested from a food that can be absorbed and used
Influenced by form of mineral (organic, inorganic), interaction with other minerals in gut or with other components e.g fibre- forms complexes that can decrease absorption of minerals
Absoprotion vs Bioavailability
Absorption- how much is absorbed
Bioavailability- how much is used for metabolism
Other factors may inhibit absorption or foods consumed together may promote or reduce bioavailability of certain foods
Ca and Fe bind each other and reduce absorption (not good to have pint of milk with steak, maybe orange juice as vitamin C increases Fe absorption)
Phosphorus- don’t really see deficiency as very abundant in food- patients with kidney failure do have decreased ability to handle it
Nutrients considered essential if meet these criteria
Present in all healthy tissues of living things
Concentration from one animal to the next is fairly consistent
Withdrawing it from diet induces reproducibility the same physiological and structural abnormalities regardless of species
Adding it to diet either reduces or prevents these abnormalities
Abnormalities induced by the deficiencies are always accompanied by specific biochemical changes
The biochemical changes can be prevented or cured when the deficiency is prevented or cured
Assessment of micronutrient requirements
Epidemiology- intake do population without deficiency symptoms
Cure deficiency
Balance- intake = loss
Dose response- plasma level, enzyme activity, metabolite, deficiency, symptom
Epidemiology
Assess health status of a large group of the population
Link to food intake survey
If no signs of deficiency in population then intake is adequate
Average intake of nutrient by population gives (over) estimate of requirement
Cure Deficiency
Need situation where deficiency arises naturally or can be induced voluntarily without long term consequences
Identify intake needed to cure the deficiency
Balance
In mature, non-lactating, non-pregnant adult assume requirement is met when
-intake=excretion in faeces and urine
Assumes no major loss in sweat, hair, wool, skin loss etc
Factorial
Uses knowledge about the various factors which contribute to the requirement
Reqt.=obligatory loss+retention+production/availability
Obligatory loss- endogenous loss, inevitable loss of nutrient from body in faeces and urine
Retention- requirement for body growth and foetal growth during pregnancy
Production- requirement for lactation
Availability- efficiency of absorption
More accurate than balance approach as takes into account some of these factors that are influencing metabolic aspects including excretion and interconversions
Ca use factorial approach to work out requirements- need to know numbers in order to calculate so can’t do it for all
Response
Identify a criterion or marker which changes in response to dietary intake
Once requirement is met there should be no changes in market value
Often difficult to achieve this so set an acceptable rate of change which is close to 0
Plot marker value against intake from sub-optimal to excess
Determine intake equivalent to selected rate of change of marker value
The marker can be a measure
-directly related to the micronutrient e.g plasma level, level in storage tissue, enzyme activity, urinary excretion
-linked to a biochemical, physiological or genetic factor which is related to the function of micronutrient in target tissues e.g metabolite level
It must respond rapidly and specifically
Flat line on graph- that’s the requirement (may not be the case for some nutrients as may be influenced by other factors)
