Vitamin D (25-OH)

Vitamin D (25-OH), also known as 25(OH)D, is a vitamin-related biomarker. It is presented as a focused marker within the vitamins category, with measurements reported in ng/mL.

Vitamin D (25-OH) is measured from a serum blood sample. The test assesses the circulating 25-OH form of Vitamin D, and the result is interpreted against the reference and optimal ranges shown with the test. Because higher values are treated as better within the provided interpretation, a result is considered in relation to where it falls across those ranges rather than viewed in isolation.

Fasting is not required for this measurement, so the sample does not require food restriction beforehand. When arranging testing, confirm the sample type and the laboratory’s reporting units so the result can be read correctly alongside the displayed ranges.

Vitamin D status may also be considered with Calcium Total, Pth, and Phosphorus. These related markers can provide additional context when a clinician is evaluating the result, particularly where mineral balance or other medical considerations are relevant. Interpretation should account for the individual’s circumstances and the laboratory’s reference information.

This result is measured in serum and reported in ng/mL. The reference range is the broader interval used to describe results within the stated reference boundaries, while the optimal range is a narrower interval within it. Because the direction is higher is better, readings are interpreted with that direction in mind, while still being considered against the relevant range.

Use the ranges displayed with the report when interpreting a number rather than judging the number on its own. A single value is not a diagnosis, and an out-of-range result should be discussed with a clinician. Fasting is not required for this measurement.

For Vitamin D (25-OH), higher values are the favorable direction. The clearest direct signal comes from Whey Protein, which increased this marker in trials, including evidence from a meta-analysis. This is the strongest basis for linking the intervention with a change in Vitamin D (25-OH) itself.

Direct trials of Resveratrol, Citrulline, Saccharomyces Boulardii, and Krill Oil did not establish a reliable change in the marker. These results should be read as unchanged overall rather than as evidence that any of these interventions consistently raise or lower Vitamin D (25-OH). Across the direct studies, rechecking occurred about 6.0 to 13.0 weeks after the intervention period.

Other interventions are listed because they target related effects, including nutrient deficiency replenishment, bone health improvement, or immune system support. These target what Vitamin D (25-OH) tracks, though trials did not measure the marker directly. Examples include Vitamin E, L-Carnitine, Vitamin B1 (Thiamine), Tai Chi, Resveratrol, Melatonin, Yoga, Cordyceps, Garlic, and Vitamin C. Their findings therefore should not be interpreted as proof that Vitamin D (25-OH) itself changes. Evidence may also differ according to the health status and population studied, so people with a medical condition should discuss the relevance of these findings with a clinician.