Lecture 10: Micronutrients - Calcium, Vitamin D, Magnesium and Zinc Flashcards
What are the functions of calcium?
- bone health
- tooth formation
- conduct nerve impulses
- regulate heartbeat
- control other cell functions
Explain the bioavailability of calcium
Diets high in oxalates, fibre, phytic acid may reduce absorption, but effects likely to be small unless gut permeability high
* Oxalates: nuts and seeds
* Phytates: grains, legumes, nuts, seeds
* Soaking and rinsing help
What happens when there is low blood calcium and when there is high blood calcium?
Low blood calcium: parathyroid hormone is reactive and it activates vitamin D
High blood calcium: calcitonin is active and it inhibits vitamin D activation and prevents calcium reabsorption into the kidneys
What is the recommended intake for calcium for adults, compared to the RDI?
Adults: 1000mg/day
RDI: 1300mg/day
What are common dairy and non-dairy sources of calcium?
Dairy:
- Plain, non-fat yogurt
- Cheddar cheese
- Non-fat milk
- 2% fat milk
- Whole-fat milk
- Blue cheese
- Feta cheese
Non-dairy:
- Soy milk
- Sardines
- Pink salmon
- MolassesSpinach
- White beans
- Pak-choi
What does calcium deficiency look like?
- Bone loss and osteoporosis
- Mobilization of calcium from bones
–> Once mobilized, it is more difficult to “pay back” bone stores; cannot be achieved by calcium alone
–> Some evidence weight bearing exercise in addition to dietary calcium and Vit D helps
–> Peak bone mass achieved around mid 20’s
Other factors influencing bone health: physical activity, vit D, vit K, hormones, smoking, excess alcohol
What does calcium toxicity look like?
Too much calcium from natural foods unlikely, but possible with supplementation
High doses can override ability of kidneys to excrete unwanted calcium, causing hypercalcemia and calcification of corneas, kidneys, and blood vessels
What does the evidence on calcium supplementation look like?
The use of calcium supplements in individuals without specific bone pathology does not have a sound evidence base, and the safety concerns suggest that the net effect could be negative
What is the primary source of vitamin D and what foods can it be found in?
Sunlight
- Fortified milk, margarine and butter
- Liver
- Egg yolks
- Fatty fish and fish oils
What is the main function of vitamin D
It maintains the blood concentration of calcium and phosphorus which are absorbed and deposited in bones
- it works with parathyroid hormone
What are three kinds of vitamin D deficiency and what do they look like?
- Rickets: In children, bones fail to calcify: growth retardation and skeletal abnormalities, bowed legs and beaded ribs
- Osteomalacia: Poor mineralization of bones in adults. Bones become softer, flexible, brittle and deformed.
- Osteoporosis: Loss of calcium from bones, reduced bone density, increased risk of fracture.
What people are at risk for vitamin D deficiency?
- Your skin not being regularly exposed to sunlight, eg: avoiding the sun, regularly wearing clothing that covers a lot of your skin, not going outside.
- Having naturally very dark skin.
What does vitamin D toxicity look like?
- Elevated blood calcium
- Calcification of soft tissues
- Harden blood vessels
- Kidney stones
What is the vitamin D status of NZ adults?
66% has equal or above the recommended average, 4.9% has deficiency
What is the relation between vitamin D and cancer?
increased risk of colorectal cancer and colorectal adenoma with low serum 25-hydroxyvitamin D levels
–> evidence for causal link is limited
What is the evidence on the usefulness of vitamin D supplements?
No clinically important benefits from Vit D supplements, expect in those with baseline vitamin D deficiency
What is the public health advice regarding vitamin D?
- Vitamin D supplements may only be beneficial for people with vitamin D deficiency
- Supports population approach to prevention (fortification or increased safe sun-exposure) rather than high risk approach of screening for vitamin D deficiency & supplementation
What is the most important function of magnesium?
It transports calcium and potassium in cells
What are some dietary sources of magnesium?
- Nuts
- Green vegetables
- Cereals (fortified)
- Wholegrains
- Bananas
- Tap and bottled water
What is the median intake of magnesium for adults and what is the RDI?
Median intake adults: 309mg
RDI men: 420mg
RDI women: 320mg
What is the most important function of zinc in the body?
Immunity
What are dietary sources of zinc with high bioavailability and low bioavailability?
High bioavailability:
Similar to iron: animal products, crustacea, mollusks, oysters, red meat, lamb’s liver, cheese
Low bioavailability: Cereal grains, legumes and nuts are rich in phytates so reduced bioavailability
What are the dietary recommendations for zinc for men and women?
Men: 14mg/day
Women: 8mg/day
What does zinc deficiency look like?
Mild deficiency:
- Stunted growth in children
- Decreased taste sensation
- Impaired immunity
Severe deficiency:
- Dwarfism
- Hypogonadism and delayed sexual maturation
- Hypopigmented hair
What does zinc toxicity look like?
- Causes metallic taste in mouth, nausea, fever, lethargy, and gastric distress
- Caused by supplementation, occupational exposures, or food poisoning
- Excessive intake interferes with copper metabolism
How can zinc help with a common cold?
- Cold duration 33% shorter for zinc lozenge groups
- Low doses and high doses equally effective
