Calcium

Question 1

Calcium

Answer 1

• 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).

Question 2

Calcium: Food Sources

Answer 2

• 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

Question 3

Calcium Roles

Answer 3

Bone Health
Cell Signalling
Muscle contraction
Blood Clotting
Neuro-transmitters

Question 4

Calcium: Bone Health - Functions

Answer 4

• 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.

Question 5

Calcium: Bone Health - Therapeutic Uses

Answer 5

• Osteoporosis
• Osteomalacia
• Fracture repair

Question 6

Calcium: Cell Signalling - Functions

Answer 6

• 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).

Question 7

Calcium: Cell Signalling - Therapeutic Uses

Answer 7

• Blood pressure
• Muscle cramps
• Muscle spasms
• Confusion
• Memory loss

Question 8

Calcium: Muscle Contraction - Functions

Answer 8

• Required (along with ATP) for the binding of actin and myosin fibres Ca is stored in muscle cells in the sarcoplasmic reticulum.

Question 9

Calcium: Muscle Contraction - Therapeutic Uses

Answer 9

• Leg cramps in pregnancy

* Preeclampsia

Question 10

Calcium: Blood Clotting - Functions

Answer 10

• Ca ions are needed to activate Vitamin dependent clotting factors

Question 11

Calcium: Blood Clotting - Therapeutic uses

Answer 11

• Bleeding disorders

* Haemorrhaging

Question 12

Calcium: Neurotransmitters - Functions

Answer 12

• Required for the conversion of tryptophan to serotonin (it is a cofactor)

Question 13

Calcium: Neurotransmitters - Therapeutic Uses

Answer 13

Mood-related PMS symptoms

Question 14

Calcium - Absorption

Answer 14

• 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.

Question 15

Calcium: Deficiency

Answer 15

• 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.

Question 16

Calcium: Factors that inhibit absorption

Answer 16

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)

Question 17

Calcium: Factors that increase excretion

Answer 17

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)

Question 18

Calcium and Dairy

Answer 18

• 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

Question 19

Calcium: Supplementation

Answer 19

• 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.

Question 20

Calcium: Nutrient Interactions

Answer 20

• 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.