Lecture 9 Flashcards
(52 cards)
Minerals
Inorganic elements that originate in the Earth that cannot be made by living organisms.
How do we get and absorb most minerals?
For humans to absorb and use minerals they must first be bound to organic compounds (containing carbon).
* Plants obtain minerals from the soil and most of the minerals in our diet come directly from plants (or indirectly from animal sources).
* Inorganic minerals may also be present in the water we drink (not useable by the body).
* Mineral levels from plants also vary depending on the mineral content in soil.
Majority of minerals in the body are
Calcium and phosphorus (approx. 75%)
Macro-minerals
Calcium (Ca); Phosphorus (P); Magnesium (Mg); Potassium (K); Sodium (Na); Chloride (Cl); Sulphur (S).
Macro-minerals exist in the body (and in food) mainly in the ionic state (as cations or anions).
Trace-minerals
Iron (Fe); Zinc (Zn); Iodine (I); Selenium (Se); Manganese (Mn); Molybdenum (Mo); Copper (Cu); Chromium (Cr); Boron (B); Fluoride (F); Silicon (Si).
Minerals also exist as components of organic compounds such as
Phosphoproteins (a protein attached to a phosphate group);
phospholipids (i.e., cell membranes);
metalloenzymes (e.g., zinc is required for ‘alcohol dehydrogenase’, which breaks down alcohol);
metalloproteins (e.g., haemoglobin; a protein with iron).
Where and how are minerals absorbed in the body?
Minerals are absorbed in the GIT (mostly in the small intestine) in their ionic state (with the exception of iron) and must be unbound from the organic compound with the help of digestive secretions (e.g., stomach acid) before being utilised by the body.
Any unabsorbed minerals are excreted in the faeces.
Key functions of minerals include
– Building tissues; e.g., skeletal system, teeth.
– Nerve and muscle function.
– Thyroid health (supporting metabolism).
– Supporting immune health.
– Components of enzymes.
Several factors can affect mineral bioavailability, including
- Mineral status in the body — in mineral deficiency states, the body upregulates absorption of the mineral. In excess states, it downregulates absorption.
- Substances present in food — can enhance (e.g., ascorbic acid and Fe) or inhibit (e.g., phytates and Fe) absorption.
- Other minerals present in food (or supplements) — can compete for absorption: (e.g., iron supplements reduce Zn absorption; Zn antagonises Cu absorption).
Minerals in supplements. Common mineral carriers.
Minerals in supplements are rarely found as pure minerals - they’re bound to carrier molecules, also called ligands.
Common mineral carriers include:
– Organic: Citrate, ascorbate, gluconate, glycinate.
– Inorganic: Oxide, carbonate, sulphide, chloride.
Calcium: found and regulated
The most abundant mineral in the body.
99% of Ca in the body is found in mineralised
connective tissues (bones and teeth).
The rest (1%) is found in extra-cellular fluid, muscle and other tissues.
Ca levels in blood are tightly regulated by parathyroid hormone (PTH), vitamin D and calcitonin (at the expense of the skeleton when dietary intake is inadequate).
Ca Food sources
Vegetable sources have the highest bioavailability, e.g., Ca from cruciferous vegetables is absorbed 2x as efficiently as Ca from dairy.
Dark green and cruciferous veg.
Nuts and seeds; e.g., sesame, almonds.
Beans; e.g., edamame, haricot.
Herbs and spices; e.g., sage, coriander leaf.
Sardines including the tiny bones.
Ca functions: bone health
Building and preserving bone mass;
Ca is an abundant mineral that binds to the collagen framework in bone, increasing its density. It is needed mostly during growth.
* Osteoporosis
* Osteomalacia
* Fracture repair
Ca functions: cell signalling
- Influences the transport of ions across the membranes of organelles.
- Nerve impulses (synapses).
- Regulates cardiac muscle function and mediates vasoconstriction (from increased concentration of Ca2+ ions in vascular smooth muscle cells).
Blood pressure
Muscle cramps
Muscle spasms
Confusion
Memory loss
Ca functions: muscle contraction
Required (along with ATP) for the binding of actin and myosin fibres — Ca is stored in muscle cells in the sarcoplasmic reticulum.
* Leg cramps in pregnancy
* Pre-eclampsia
Ca functions: blood clotting
Ca ions are needed to activate vitamin-dependent clotting factors.
* Bleeding disorders
* Haemorrhaging
Ca functions: neuro-transmitters
Required for the conversion of tryptophan to serotonin (it is a co-factor).
* Mood-related PMS symptoms
Ca Absorption
Ca is absorbed by all parts of the small intestine, but especially in the duodenum, where conditions are more acidic due to the acidic chyme that enters from the stomach, which increases absorption.
50%–70% of ingested Ca is not absorbed and lost in the faeces.
Ca Active absorption
Active absorption is controlled by vitamin D (calcitriol), which binds to the enterocyte vitamin D receptor (VDR) and increases the transcription of calcium transporters called calbindins, which increase calcium movement from the GIT to the blood.
Ca Passive absorption
Passive absorption occurs without vit. D, when Ca is consumed.
Ca deficiency
Calcium deficiency is extremely rare as blood levels are typically maintained even with inadequate intake at the expense of bones.
Ca Factors that inhibit absorption
Low vitamin D status
Low stomach acid (HCl dissolves calcium salts)
High intake of phytates / oxalates
Gastrointestinal dysfunction
Other minerals (e.g., Mg, Fe, Zn)
Ca Factors that increase excretion
Menopause (low oestrogen)
High animal-protein diets (due to high levels of urea and sulphuric acid)
High-salt diets
High caffeine intake
Medications
Ca and dairy
Dairy is high in sulphur-based amino acids (e.g., methionine), which can increase sulphuric acid formation — leaching calcium (an alkaline mineral) from bones.
High intake of other animal proteins (i.e., meat) contributes to calcium loss from bone.
