Calcium Flashcards
Calcium
- Calcium (Ca) is the most abundant mineral in the body accounting for 2% of body weight and 39% of the body’s mineral content.
- 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).
Calcium: Food Sources
- Calcium is found mostly in plant and dairy foods.
- Vegetable sources have the highest bioavailability e.g. Ca from cruciferous vegetables is absorbed 2x as efficiently as Ca from dairy.
Dark Green leafy vegatables; kale, watercress, pak choi, broccoli. Almonds, Sesame Sardines (incl bones) Cow's mik, Beans, peas, edamame
Calcium Roles
Bone Health Cell Signalling Muscle contraction Blood Clotting Neuro-transmitters
Calcium: Bone Health - Functions
• Building & preserving bone mass ; calcium is an abundant mineral that binds to the collagen framework in bone, increasing its density. It is hence needed mostly during growth.
Calcium: Bone Health - Therapeutic Uses
- Osteoporosis
- Osteomalacia
- Fracture repair
Calcium: Cell Signalling - Functions
- Influences the transport of ions across the membranes of organelles.
- Nerve impulses (synapses)
- Regulates cardiac muscle function and mediates vasoconstriction from increased concentration of Ca 2+ ions in vascular smooth muscle cells).
Calcium: Cell Signalling - Therapeutic Uses
- Blood pressure
- Muscle cramps
- Muscle spasms
- Confusion
- Memory loss
Calcium: Muscle Contraction - Functions
• Required (along with ATP) for the binding of actin and myosin fibres Ca is stored in muscle cells in the sarcoplasmic reticulum.
Calcium: Muscle Contraction - Therapeutic Uses
- Leg cramps in pregnancy
* Preeclampsia
Calcium: Blood Clotting - Functions
• Ca ions are needed to activate Vitamin dependent clotting factors
Calcium: Blood Clotting - Therapeutic uses
- Bleeding disorders
* Haemorrhaging
Calcium: Neurotransmitters - Functions
• Required for the conversion of tryptophan to serotonin (it is a cofactor)
Calcium: Neurotransmitters - Therapeutic Uses
Mood-related PMS symptoms
Calcium - 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.
• Ca is absorbed both actively and passively:
- 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.
- Passive absorption occurs without Vitamin D, when Ca is consumed.
• 50% - 70% of ingested Ca is not absorbed and lost in the faeces.
Calcium: Deficiency
- Calcium deficiency is extremely rare as blood levels are typically maintained even with inadequate intake at the expense of bones.
- Unlike other diseases, loss of bone mineral density is asymptomatic.
Calcium: 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)
Calcium: 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 (see drug interactions)
Calcium and Dairy
- The protein component of cow’s milk is likely the problem, as dairy is high in sulphur based amino acids (e.g. methionine), which can increase sulphuric acid formation leaching calcium (an alkaline mineral) from bones
- Countries with a high dairy consumption have often also a high intake of other animal proteins (i.e. meat) which contributes to calcium loss from bone
Calcium: Supplementation
- Studies mostly show that Calcium supplementation is ineffective at preserving bone density when dietary intake is sufficient and it can present risks: e.g. kidney stones ; soft tissue calcification , especially when vitamin D and K levels are inadequate.
- Although calcium carbonate is often recommended, calcium citrate is far easier to absorb.
A maximum absorption of calcium is usually 500mg per sitting.
Calcium: Nutrient Interactions
- Mg competes for absorption with Calcium. High supplemental Ca doses (2g/day for 11 30 days) decreases Mg absorption and plasma levels.
- Some studies show that Ca supplementation decreases absorption of non haem iron in a dose dependent manner.
- High Ca intake (either from high dairy or supplements) decreases Zn absorption. High Zn intake also interferes with Ca absorption if dietary intake is low.
- High Ca intake has been reported to interfere with Phosphorus absorption.
