Vitamin D & Calcium Flashcards
What are the main sources of vitamin D?
Sunlight (UVB + Warmth)
Fish Oils, Egg Yolks. Fortified margarines and cereals
What are the two main forms of vitamin D that can be taken in the diet?
Cholecalciferol (natural)
Ergocalciferol (synthetic)
Describe the mechanism from sunlight to active vitamin D
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)
How is vitamin D degraded in the body?
Degraded by 24-hydroxylase
Name a non PTH-calcium axis function of vitamin D
Receptors
Name 3 conditions associated with vitamin D deficiency in epidemioloigcal studies
MS, Cancer, thyroid autoimmune diseases, DM and CVD
How do you assess vitamin D status?
Plasma 25(OH)D reflect vitamin D stores
Vitamin D assays -> HPLC or LC-MS -> disputed due to poor agreement on labratory use
Where is vitamin D stored?
Adipose tissue & Liver
How long can vitamin D stores last?
2 Years `
What is the RNI of vitamin D
10ug/d (400IU/d)
What is the RNI of 400IU/d of vitamin D based on?
Based on the average amount of vitamin D required to maintain serum 25(OH)D concentrations >25nmol/L when UVB sunshine is minimal
What is Public Health England additional advice with regards to vitamin D?
Everyone should take 10ug/day supplement in autumn and winter
Anyone at risk of vitamin D deficiency should take a supplement all year round
What is the ‘sunlight prescription’ required for someone in London (lat 51)?
8-12min of hands, face & arms 2-3 times/week
Give 3 factors that affect light exposure, geography & subsequent vitamin D deficiency
Not sufficient wavelength between october & march
High latitude results in less light & warmth exposure required
What are the clinical syndromes in adults and children that have vitamin D deficiency
Rickets & Osteomalacia
What happens in vitamin D toxicity?
Can only happen with supplementation
Results in hypercalcaemia (resulting in calcification of soft tissues, kidney stones, coma, cardiac failure)
What regulates PTH secretion?
Low calcium & vitamin D increases secretion
Give as many functions of PTH that results in calcium concentration increases
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
What is the recommended requirements in an adult for calcium?
700mg/day
How much increase should lactating women add to calcium intake?
500mg
Why is calcium recomendations higher in teenagers?
Bone deposition to support growth
Why are vegans at risk of calcium deficiency?
Low dietary intake and high intake of phytates & oxalate which prevent absorption
What is a known cause of excessive calcium?
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
Name 5 food sources of calcium
Milk, broccoli, spinach, cheese, white beans, rhubarb
