Vit D supplementation can lower 1,25-(OH)2D levels.

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> " He had low 25-hydroxyvitamin D (25-OHD) and high 1,25-(OH)2D serum

> levels. Intramuscular vitamin D2 administration produced radiological

> and biochemical evidence of recovery. "

>

> Which I read as D2 supplementation results in higher 25D and lower

> 125D (i.e. recovery).

The reason for this are probably explained in the following study,

which showed that vitamin D supplementation can decrease the

conversion rate of 25(OH)D3 (25D) to 1,25(OH)2D3 (125D). Extra

vitamin D supplementation does this, because it increases the

conversion of 25(OH)D3 (25D) to 24,25(OH)2D3:

http://www.nutrition.org/cgi/content/full/132/9/2644

" Cholecalciferol (vitamin D3) is essential for the hormonal regulation

of intestinal Ca absorption. After its first hydroxylation in the

liver into 25(OH)D3, it is hydroxylated mainly in the kidney into

1,25(OH)2D3 and 24,25(OH)2D3 with the aid of 1{alpha}-hydroxylase and

24-hydroxylase, respectively. "

" In hVitD (higher vitamin D supplemented) dogs, the greater plasma

24,25(OH)2D3 concentration and the enhanced metabolic clearance rate

(MCR) of 1,25(OH)2D3 indicated upregulated 24-hydroxylase activity.

The increased MCR of 1,25(OH)2D3 decreased plasma 1,25(OH)2D3

concentrations. "

" Thus, during positive Ca balance, high vitamin D3 intake (as in the

hVitD group) enhances 24-hydroxylase activity and results in enhanced

production of 24,25(OH)2D3 and probably competitive inhibition of the

synthesis of 1,25(OH)2D3 from 25(OH)D3. "