Sunlight, 25-D, and 1,25-D

[Guest guest]

Rodney,

Just to back-pedal a bit, and caution that the previous article may be

true, but unrelated:

There are all sorts of control mechanisms in the body to carefully

regulate the serum level of 1,25-D. Usually, giving cholecalciferol,

or sunlight, for example, results in increases in the serum 25-D

level, but no change in serum levels of 1,25-D. This is because most

of the enzyme that converts 25-D to 1,25-D is in the kidney, and this

enzyme is carefully regulated. The liver conversion of cholecalciferol

to 25-D may be much more sensitive to how much cholecalciferol is

available.

So, for example, take this study as an example:

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve & db=pubmed & dopt=Abstra\

ct & list_uids=7656883 & query_hl=3 & itool=pubmed_DocSum

Eur J Clin Nutr. 1995 Jun;49(6):400-7.

Sunlight increases serum 25(OH) vitamin D concentration whereas

1,25(OH)2D3 is unaffected. Results from a general population study in

Goteborg, Sweden (The WHO MONICA Project).

etc. etc. Some very recent evidence, though, suggests that the cells

lining blood vessels may have the 1-hydroxylase enzyme, and they may

convert 25-D to 1,25-D locally, and then get a local 1,25 D effect

that is not measurable by testing the serum level of 1,25-D.

So it's complicated - lot's of research interest and activity, and no

one knows all of the answers. But remember that the previous study I

cited was the effect of 1,25-D infusion, and not 25-D, on the blood

pressure. Plus, there are other studies where they look at serum

level of 1,25-D and blood pressure, as was discussed before, and where

they find an INVERSE relationship (high 1,25-D associating with lower

blood pressures).