Vitamin D, Calcium, Phosphorus, & Magnesium
Where is magnesium stored
60% in bones
Homeostasis and phposphorus
70% in blood circulates as part of phospholipids (lipoproteins, cells, platelets) Much dietary P absorbed so proper renal excretion is important Serum levels have tight control via PTH and 1,25(OH)2 cholecalciferol Protein identified- fibroblast growth factor 23 and klotho Genetic defect-> calcification of soft tissue
Where is most calcium
99% in bones and teeth 40% all minerals i body
How dietary sources move vitamin D
Absorbed from micelles in intestinal tract by passive diffusion carried by chylomicrons-> adipocytes Hylomicron remnants drop off remaining vitamin D-> liver for metabolism
How is calcium absorbed
Absorbed only in ionized form, transport through intestinal cell by diffusion or with calbindin
Absorption of CA: favoring factors
Acidic environment in upper intestinal tract Normal digestive activity and motility of intestines Dietary CA and P in equal amounts Vitamin D available Need more during pregnancy Low Ca intake Availability of PTH Presence of lactose
Metabolism of Vitamin D
Activated by enzymes in liver and kidney Liver: hydroxy group added to 25th C to make 25-OH vitamin D3 (catalyze by 25-hydroxylase reaction) Kidney: hydroxy group added to 1st C= 1,25 (OH)2 vitamin D3 1 alpha-hydroxylates catalyzes the reaction
Vitamin D is stored in
Adipocytes and circulated in blood until the active form is needed
The active form of vitamin D
Aids in calcium absorption Cholecalciferol->liver->calcifediol->kidney-> calcitriol
Hindering factors for calcium
Alkaline state in intestinal tract Increase wheat bran Excess P, Fe, An Mg in proportion to Ca Phytic acid, oxalacetate acid, unabsorbed FA Vit D deficiency Aging Menopause
Absorption of magnesium
Along small intestine, limited in colon
Functions of calcium
Bone development ad maintenance (hydroxyapatite, osteocalcin and matrix Gla protein) Bloo clot- Gla proteins bind Ca Transmission of nerve impulses to target cells Muscle contraction Cell metabolism- activates enzymes
Role of magnesium
Bone- crystal lattice development and surface o bone (Mg pool) ATP dependent reactions 300 enzyme-catalyze reactions-key in glycolysis Anti inflammatory role- decreased levels leads to asthma, arthritis, neuroinfammation PTH excretion, hydroxylation of vitamin D
Genomics of vitamin D
Calcitriol binds to VDR in nucleus- I handed or inhibits the translation of genes
Vitamin D is a prohormone from
Cholesterol
Low intake of magnesium leads to
Chronic diseases
How the sun synthesizes vitamin D
Converts 7-dehydrocholesterol-> provitamins D3 by UV-light-> Vit D3 (cholecaliferol) in skin -> blood by D binding protein
Food contains what type of vitamin D
D2 (ergosterol) which goes to the liver and kidney= 1,25 dihyroxycholecalciferol.
Deficiency and toxicity of phosphorus
Deficiency is rare Toxicity is rare but can be found in infants with high P formulas
Roles of phosphorus
Energy metabolism- P bond in ATp, GTP and creatine phosphate drives most energy reactions Glycogen production Cell signaling DNA and RNA dependent Phospholipids Essential for teeth and bone structure as part of the hydroxyapatite- calcium phosphate crystals
Increased intake of magnesium leads to
Enhances Ca, P, K excretion which leads to renal damage and insufficiency
Calcium and Bone mass
Growth, osteoblasts exceeds osteoclasts activity (make more than break) More mass in high stress areas Peak mass between age 20-30 Loss in mid-adulthood High loss at menopause
Low intake of magnesium caused by
Highly refined foods
How is calcium transported
In blood by being boun to proteins-albumin and PAB Competed w/ sulfate, phosphate, or citrate Free or ionized (50%)
Where is phosphorus absorbed
In the small intestine in its organic form- must be liberated by digestive enzymes- vitamin D stimulates absorption
Consequences of hypercalcemia
Kidney stones and calcification of tissue
2nd most abundant mineral
Phosphorus
Deficiencies of Magnesium
Rare- vomiting, diarrhea, alcohol abuse, real and endocrine disease, protein malnutrition, increased diuretics
Functions of Vitamin D
Regulate blood calcium level Kidney: PTH reabsorbs CA through calbindin D28K Intestine: absorb CA from food by calbindin D9k Bone: PTH release Ca from bone through RANKL that matures osteoclasts Overabsorption of calcium (hyperccalcemia), increase CA excretion CA deposits in kidneys, heart, blood vessels= narrow arteries and aorta, facial change, mental retardation
Deficiency of vitamin D
Rickets=Or bone mineralization in kids Osteomalacia-soft bones in adults Resistant problems with synthesis of active form/defective receptor binding
Low levels of Mg leads to
T2DM, metabolic hadron, cancer, ischemic heart disease
Where do we get vitamin d
THE SUN!!!!!....fatty fish (salmon, herring) fortified milk, fortified cereal....
Where is calcium stored
Technically in bone
What increases absorption of magnesium
Vitamin D
Causes of deficiency in the elderly (vitamin D)
Low sun exposure Impaired synthesis in skin Low dietary intake Malabsorption of dietary vitamin D Low 1,25-DiOH D3 from low 1 alpha hydroxylates activity in kidney
Regulation of blood calcium
Maintained @ Brice of bone calcium High blood calcium-PTH- retains calcium from excretion, increased calcium absorption via increased calcitriol, increased calcium release from bone Lowering blood calcium- calcitonin - decrease PTH and calcitriol
What decreased absorption of pphosphorus
Meals with high Mg or Ca Form chelates in intestinal lumen leads to decreased absorption
How to get too much vitamin D
Megadoses of supplements, NOT the sun
Deficiency of calcium
Osteoporosis-leads to fractures Osteopenia-decreased bone mass
