Many of my clients with dogs in kidney failure are confused about supplementing with vitamin D. They read websites and belong to a variety of on-line chat groups that offer opinions, but confusion results due to opinions often being so different from one another. It’s stressful enough to have a sick dog without adding confusion to the mix because someone says to restrict vitamin D. Ah, but there’s vitamin D and and then there’s vitamin D! It’s a bit of a drunkard’s walk, so bear with me.
In kidney insufficiency and in failure, the kidney retains phosphorus instead of excreting enough of it. This signals the parathyroid gland that there is a phosphorus-calcium imbalance. That balance is one of the critical ratios and balances for all tissues and so, action is taken.
The parathyroid gland releases parathyroid hormone (PTH) which flows throughout the circulation and specifically signals the gut to absorb more calcium and the bone to release minerals into the bloodstream. That helps increase calcium in circulation and make the Ca/Phos balance better. Meanwhile, the failing kidney still isn’t excreting phosphorus well, so it keeps building up, and that causes an on-going release of PTH, which has consequences.
In addition PTH goes to the liver and gets it to release vitamin D precursor into the circulation.
That pre-vitamin D (vitamin D2 or hydrocholecalciferol) goes to the kidney, which (early on) is still able to turn it into vitamin D3 (dihydro-cholecalciferol, calcitriol). D3 helps with the calcium absorption from the intestinal tract. AND (here’s the key part to the treatment idea) it flows to the parathyroid gland and shuts off PTH release. So what?
PTH in high amounts is toxic to the kidney, which is already in failure and doesn’t need any more poisoning. Without the D3, PTH keeps flowing and poisoning the kidney while increasing calcium uptake. With D3, PTH is kept in check and the kidney suffers less. This is one of the reasons that fish body oils (think wild salmon oil) can play a key role in helping compromised kidneys while plant-based oil (which provide some D2) are deleterious when kidneys aren’t functioning well.
D3 is also known as Calcitriol and given early in kidney failure, will help reduce the excess release of PTH and helps the kidney that way.
Read more about kidney function and disease here.