Vitamin D

Vitamin D was discovered because it prevents

rickets in children

Vitamin D AKA calciferol comes from what 2 sources

• plant

  • ergocalciferol D2

• animal

  • cholecalciferol D3

What is another way VD can be made

when the skin is exposed to the sun’s UV radiation because 7-dehydrocholesterol is found in the skin

D3 travels through the blood stream to the

liver where it is converted to 25-oh calcidiol, 5x as active as cholecalciferol

After D3 is converted to calcidiol where can it travel

the kidneys where it becomes 1,25-dioh calcitriol this is 10x as active and the most active form

Best food sources of VD

fatty fish, fish oils, fortifies foods

Foods fortified with VD

milk, orange juice, yogurt, cereal, infant formula

Sunlight for VD

• when conditions are right 15-30 minutes exposure can produce 100x more VD than a serving of fortified milk

• even 5-10 minutes of arms and legs can generate 5x the RDA for VD

Whose most likely to be deficient

• 33rd parallel (lex)

• darker skin tones, decreased synthesis, melanin blocks UV rays

• tanning beds not the same - wrinkles

Factors that influence skin production of vitamin D

• cloud coverage

• sunscreen

• skin tone

• season

• say

• air pollution

• age

• altitude

• latitude

VD supplements

provide the vitamin as D3 cholecalciferol

does VD require digestion?

no

How is VD absorbed

50% is absorbed by passive diffusion

VD is packaged with

chylomicrons with other fats and released into lymphatic system and ultimately general circulation

1,25diOH Calcitrol is the

most active form

the liver forms 25-OH by

1-alpha-hydroxylase

Why is VD important

-calcium homeostasis
-cell differentiation
-regulating immune function
-reducing inflammation
-muscle structure and function

when blood calcium falls, _______ is released from what?

PTH, parathyroid gland

the rise in PTH acts on the kidneys and increases the activity of

1-hydroxylase, this increases the amount of calcitriol produced

what are the effects of elevated calcitriol when blood calcium is down?

-stimulates the reabsorption of calcium in the kidneys so less is excreted
-promotes the active, energy requiring absorption of calcium through the stimulation of calcium binding in the gut.

when blood calcium falls explain what happens?

-when blood calcium falls, PTH is secreted from the parathyroid gland.
-this will stimulate vitamin D activity
-increase osteoclast (bone breakdown)
-increase in calcium retention in the kidney
-increase calcium absorption in the small intestine

when blood calcium rises, what happens?

-blood calcium rises
-calcitonin is released from the thyroid gland
-this inhibits vitamin D activity
-increases osteoblast activity (bone building)
-decreases calcium retention in the kidneys
-decreases calcium absorption in the small intestine
-blood calcium falls and calcitonin secretion is inhibited.

what are the two ways that vitamin D can control blood calcium?

-non-genomic: calcitriol will bind to cell membrane receptor and includes an intracellular cell signalings cascade. this will cause a pretty quick cellular response which may facilitate any of the functions listed above.
-genomic: calcitriol enters the cell, moves through the cytosol and enters the nucleus. once in the nucleus, calcitriol will bind to a vitamin D receptor, which then becomes an activated transcription factor. this calcitriol-VDR complex can then bind DNA directly on specific DNA sequences. this binding influences the contraction or expansion of chromatin allowing for transcription to be activated or repressed.

what are the symptoms of vitamin D toxicity?

-calcium deposits
-poor growth
-muscle weakness
-mental confusion.

what can people get from a vitamin D deficiency?

Rickets: malnutrition of bones in children, they must supplement vitamin D in kids and kids being breastfed still.
-osteomalacia: this is the softening of bones (bending spine, waddling legs, bowed legs, old women.