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Foundations of Nutrition > Vitamin D & Calcium > Flashcards

Vitamin D & Calcium Flashcards

1
Q

What are the main sources of vitamin D?

A

Sunlight (UVB + Warmth)

Fish Oils, Egg Yolks. Fortified margarines and cereals

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2
Q

What are the two main forms of vitamin D that can be taken in the diet?

A

Cholecalciferol (natural)

Ergocalciferol (synthetic)

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3
Q

Describe the mechanism from sunlight to active vitamin D

A

UVB & Warmth converts cutaneous 7-dehydrocholesterol to vitamin D(3)

Vitamin D converted to 25-hydroxyvitaminD by liver (25-hydroxylase)

25-(OH)D is then converted to 1,25-dihydroxyvitaminD (1,25-(OH)2D in the kidney (1-alpha hydroxylase)

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4
Q

How is vitamin D degraded in the body?

A

Degraded by 24-hydroxylase

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5
Q

Name a non PTH-calcium axis function of vitamin D

A

Receptors

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6
Q

Name 3 conditions associated with vitamin D deficiency in epidemioloigcal studies

A

MS, Cancer, thyroid autoimmune diseases, DM and CVD

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7
Q

How do you assess vitamin D status?

A

Plasma 25(OH)D reflect vitamin D stores

Vitamin D assays -> HPLC or LC-MS -> disputed due to poor agreement on labratory use

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8
Q

Where is vitamin D stored?

A

Adipose tissue & Liver

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9
Q

How long can vitamin D stores last?

A

2 Years `

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10
Q

What is the RNI of vitamin D

A

10ug/d (400IU/d)

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11
Q

What is the RNI of 400IU/d of vitamin D based on?

A

Based on the average amount of vitamin D required to maintain serum 25(OH)D concentrations >25nmol/L when UVB sunshine is minimal

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12
Q

What is Public Health England additional advice with regards to vitamin D?

A

Everyone should take 10ug/day supplement in autumn and winter

Anyone at risk of vitamin D deficiency should take a supplement all year round

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13
Q

What is the ‘sunlight prescription’ required for someone in London (lat 51)?

A

8-12min of hands, face & arms 2-3 times/week

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14
Q

Give 3 factors that affect light exposure, geography & subsequent vitamin D deficiency

A

Not sufficient wavelength between october & march

High latitude results in less light & warmth exposure required

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15
Q

What are the clinical syndromes in adults and children that have vitamin D deficiency

A

Rickets & Osteomalacia

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16
Q

What happens in vitamin D toxicity?

A

Can only happen with supplementation

Results in hypercalcaemia (resulting in calcification of soft tissues, kidney stones, coma, cardiac failure)

17
Q

What regulates PTH secretion?

A

Low calcium & vitamin D increases secretion

18
Q

Give as many functions of PTH that results in calcium concentration increases

A

Increases conversion of 25(OH)D to 1,25(OH)2D in the kidney to increase vitamin D functions (e.g. increase calcium reabsorption in the gut)

Activation of osteoclasts to increase bone calcium resorption

Increases calcium reabsorption in kidney

19
Q

What is the recommended requirements in an adult for calcium?

A

700mg/day

20
Q

How much increase should lactating women add to calcium intake?

A

500mg

21
Q

Why is calcium recomendations higher in teenagers?

A

Bone deposition to support growth

22
Q

Why are vegans at risk of calcium deficiency?

A

Low dietary intake and high intake of phytates & oxalate which prevent absorption

23
Q

What is a known cause of excessive calcium?

A

Condition causing abnormalities in the PTH-Caclium-VitD axis -> i.e. a PTH secreting tumour or kidney failure

‘Milk alkali syndrome’ i.e. chronic consumption of milk & antacids increasing absorption

24
Q

Name 5 food sources of calcium

A

Milk, broccoli, spinach, cheese, white beans, rhubarb

25
Q

Describe the distribution & role of calcium in the body

A

99% hydroxyapetite in bone giving strcutre & function & acts as a calcium resevoir

1% free ions in muscle, nerves, plasma, signalling molecules

26
Q

Where is calcium absorbed in the gut?

A

Duodenum (+ileum & colon)

27
Q

What are the two absorption mechanisms?

A

Active & Passive

Active relies on vitamin D to induce the production of calcium binding proteins to increase caclium absorption

Passive absorption is dependent on calcium intake

28
Q

How much calcium is absorbed if you consume 1000mg?

A

15-20%

29
Q

What dietary factors increases calcium absorption?

A

Gastric Acid, Citrate, Amino Acids, Milk

30
Q

What dietary factors decreases absorption of calcium?

A

Phytates, oxalate, fibre & fat malabsorption

31
Q

What drug blocks calcium absorption?

A

Corticosteroids

Foundations of Nutrition (13 decks)

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