The guidelines also recommend testing with an assay that measures levels of circulating 25-hydroxy vitamin D
or 25(OH) D.
The researchers measured blood levels of 25-hydroxy vitamin D
with an immunoassay.
Serum 25-hydroxy vitamin D
and the incidence of acute viral respiratory tract infections in healthy adults.
The results indicated that supplementation with the equivalent of about 8,500 IU of vitamin D3 daily significantly increased serum 25-hydroxy vitamin D
levels and improved insulin sensitivity (p=0.
Vitamin D deficiency is an important concern, but assays for serum 25-hydroxy vitamin D
(25-OH-D), (1) the accepted marker for vitamin D nutritional status, are not standardized.
Whereas calcium intake at baseline was already high, women entering the study had fairly low vitamin D levels at baseline; 85% of women had a serum 25-hydroxy vitamin D
level below 30 ng/mL, suggesting vitamin D insufficiency.
Other studies have shown that people who have relatively high blood levels of 25-hydroxy vitamin D
(a marker of vitamin D nutritional status) have a lower incidence of breast, prostate and colon cancer compared to people with lower vitamin D status (Garland et al.
Four had a serum 25-hydroxy vitamin D
(25-OHD) level greater than 30 ng/mL, a value considered to be optimal.
Once vitamin D is available, the body converts it first into 25-hydroxy vitamin D
and then into 1,25-dihydroxy vitamin D (1,25-D).
The D3 form of the vitamin has been demonstrated as far more potent than D2, the other commonly used supplemental form, in raising circulating levels of 25-hydroxy vitamin D
, the blood marker that best indicates the body's vitamin D status.
In the kidney, 25-hydroxy vitamin D
converts into the active form of the vitamin that helps regulate calcium and phosphate levels and can be measured in blood.
It is intended for the quantitative determination of 25-hydroxy vitamin D
in human serum and plasma to aid in the assessment of vitamin D sufficiency.