Introduction to Micronutrients Flashcards by Poppy Greacen

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

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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

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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

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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

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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

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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

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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

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Minerals Classification

Macrominerals
-Ca, P, S, K, Na, Cl, Mg
Trace elements
-Fe, Zn, Cu, Se, I, Mn, Cr, Co

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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

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Absoprotion vs Bioavailability

Absorption- how much is absorbed

Bioavailability- how much is used for metabolism

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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

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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

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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

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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

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Cure Deficiency

Need situation where deficiency arises naturally or can be induced voluntarily without long term consequences
Identify intake needed to cure the deficiency

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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

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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

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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)

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Genetics important in predicting nutritional requirements

Some individuals may have different polymorphisms, different response rates e.g homozygous and respond bluntly or heterozygous and respond rapidly

There is a good reserve of nutrients in case of deficiency

Short term functions will never be compromised- body will always prioritise those over rapidity and support for bone mass- at expense of skeletal Ca, blood Ca will be maintained
Deficiency symptoms for some nutrients will appear quicker than others as stores are different (vitamin A has really good long term storage capacity in liver)
Aim to maintain biochemical function for as long as possible- first stores deplete, then failure to maintain tissue levels and then deficiency symptoms appear when biochemical function is compromised

Epidemiology Disadvantages

Imprecise and unsure if large over estimate or marginal

Cure Deficiency Disadvantages

Limited in opportunity and numbers of subjects

Balance studies Disadvantages

Body attempts to maintain homeostasis when intake changes by moderating usage, excretion, etc, so balance may not be true balance for that intake

Factorial Disadvantages

Depends on accuracy with which individual factors are known, obligatory losses and efficiency of absorption may vary with intake level

Dose response disadvantages

May depend on other components of diet, need to determine for different physiological states, different markers may indicate different requirements, must select a sensitive marker

When you set a requirement for a vitamin and mineral you assume all other requirements have been met- Ca and vitamin D have synergistic effect, vitamin D increases Ca absorption from intestine- should consider both when setting requirements but don't

Determine requirements in the most appropriate way for each micronutrient then add a bit as a safety factor Current thoughts- although requirement may prevent deficiency symptoms it may not be optimal to prevent other conditions developing e.g cancer

Premise that micronutrients when go beyond certain level may protect against disease

And not just simply cure deficiency

Factors leading to the appearance of deficiency symptoms

Intake doesn't meet requirement Inadequate intake of right food- crop failure, poverty, ignorance of balanced diet, anorexia, illness, dental problems Intake appears to meet requirement Reduced absorption- intestinal disorders, reduced availability due to interactions between dietary constituents Increased requirements- physical activity, growth, pregnancy, infection, drug therapy Increased losses- sweat, diuretics, lactation Antagonists- other compounds inhibiting action

Nutrition requirements

Proper whole body function is determined by the intake and use of the appropriate type and amount of nutrient which varies from one individual or adult to another

Nutritional requirements are principally governed by

1) specific nutrient requirement 2) energy requirement Relationship between 1 and 2

Energy provision

Fats Carbohydrates Proteins

Tissue formation/maintenance/products

``` Proteins Carbohydrates Fats Minerals Vitamins ```

Requirements may also be dependent on a specific role of a nutrient

Complex carbs improve gut function Vitamins and minerals have a wide range of functions- difficulty with requirements as they have a very broad role so it's difficult to know what role requirements should be based on Vitamin A- antioxidant role and vision

DRVs

Estimates of the requirements for groups of people and are not recommendations or goals for individuals They aren't applicable to children under 5

Lower Reference Nutrient Intake (LRNI)

Level of intake below which most people's requirements will not be met. Intake below which you might expect deficiency to occur

Estimated Average Requirement (EAR)

Average requirements of groups of similar people

RNI

Level of intake at which everyone's requirements would be met. Only 2.5% population have requirement higher than RNI

19% UK girls have intake below RNI- problem as only 2.5% should be lower

If all nutrients are over RDA then can be confident that no deficiencies- never sure but high level of confidence

Criteria of adequacy (increasing intake)

``` Toxicity Pharmacological effects Prevention of unrelated diseases Saturation of body pools Adequate to prevent deficiency Biochemical deficiency Clinical deficiency Life threatening deficiency ```

Average requirements of groups of similar people

Difficult because -not same from day to day -considerable variation in children due to difference in activity -daily needs for maintenance of existing tissues and growth -pregnant/lactating women additional allowances Solution -average requirements for similar groups e.g age bands, state of pregnancy

Excreted nutrients

Find out how much of a nutrient the body is using each day All routes of excretion of a nutrient and all of its by products must be taken into account Amounts to be replaced can then be determined Only excreted nutrients

Non-excreted nutrients

Blood levels Use labelled isotope to measure turnover Amount needed to reserve deficiency state Expired gas measurements and heat output

Others difficult to determine

``` Vitamin D (sunlight source, external source) Nutrients with large body source e.g vitamin A and vitamin B12 Requirement based on population intake to stay healthy ```

Minimum requirement not determined

Sodium Magnesium Vitamin E Molybdenum/cobalt Abundant in food, deficiency only in disease where there is inability to absorb

Vitamins

Organic compounds that are required in small amounts for normal functioning of the body and maintenance of metabolic integrity They are essential for the life and well-being of organisms Cannot be synthesised in the body Deficiency results in specific deficiency symptoms which can be cured by addition of the vitamin to the diet