Vitamin Cycles

Question 1

What is the vitamin D cycle?

Answer 1

Dietary 7-dehydrocholesterol

Converted by UV to previtamin D3 then to vitamin D3

Liver 25-hydroxylation to 25-HO D3

Kidney 1-hydroxylation to 1,25-HO D3

Question 2

What are sources of vitamin D?

Answer 2

Fish oils
Egg yolks
Liver

Question 3

How is vitamin D regulated?

Answer 3

Kidney, intestine, bone and parathyroid glands all coordinate.

Major regulators: PTH, calcium, phosphate and 1,25-vitamin D3 itself

Actions:
PTH increases 1,25-vitamin D3
Calcium decreases 1,25-vitamin D3
Phosphate decreases 1,25-vitamin D3
1,25-vitamin D3 has a negative feedback loop on its own production