For you Type 2 diabetics who are taking Metformin: maybe have your endocrinologist check your blood levels of B12 on your next blood draw. I just learned this morning that Metformin interferes with B12 absorption, so even if you’re getting enough in your diet, you could still be short due to the Metformin.

And, while you’re at it, have her/him also check your vitamin D levels. This seems worthwhile with all the reports of people having unsuspected vitamin deficiencies, especially given all the things that vitamin D does for you.

Here’s some useful info:

There are two vitamin D tests — 1,25(OH)D and 25(OH)D.

25(OH)D is the better marker of overall D status. It is this marker that is most strongly associated with overall health.

The correct test is 25(OH)D, also called 25-hydroxyvitamin D.

The optimal levels shown below are taken from healthy people from the tropical or subtropical parts of the world where they are receiving healthy sun exposures. It seems more than reasonable to assume that these values are in fact reflective of an optimal human requirement.

Dr. Michael Hollick is one of the top vitamin D researchers in the world and he has been advocating higher reference ranges, though not as high as the ones suggested here.

(Holick MF. Calcium and Vitamin D. Diagnostics and Therapeutics. Clin Lab Med. 2000 Sep;20(3):569-90)

Optimal 25-hydroxyvitamin D values are: 45-50 ng/ml or 115-128 nmol/l

Normal 25-hydroxyvitamin D lab values are: 20-56 ng/ml 50-140 nmol/l

If you have the above test performed, please recognize that many commercial labs are using the older dated reference ranges. The above values are the newest ones from the clinical research.

There are a number of different companies that have FDA approval to perform vitamin D testing. The gold standard company though is DiaSorin. Quest labs is the largest commercial lab in the US and they use this company to measure 25 hydroxy D levels. However, many other commercial labs don’t. So if you do not have your test done at Quest labs please contact the lab directly to find out which assay is being used. Your test results will not be accurate and you can not use the values in the table above unless the D is measured with a DiaSorin assay. The extra hassle is definitely worth it, believe me. You will only need to do this once though, as the labs do not switch assays. However, if your lab is not using the DiaSorin assay you could ask them to switch to the gold standard.