What do studies say about Vitamin D Labor?

The evidence on Vitamin D laboratory testing and supplementation is nuanced. Observational studies consistently link low 25-hydroxyvitamin D levels with increased risk of fractures, infections, cardiovascular disease, and some cancers. However, large randomized controlled trials (RCTs) such as VITAL (PMID: 31959942) found limited benefits of supplementation in generally healthy adults without deficiency. A meta-analysis (PMID: 25664854) reported a modest reduction in all-cause mortality but no significant effect on cardiovascular events. Strong evidence supports vitamin D supplementation for preventing rickets and osteomalacia in confirmed deficiency. For general health, routine testing and supplementation in unselected populations remain controversial. Many direct-to-consumer tests overstate the clinical relevance of single measurements. Interpretation depends on assay method (e.g., LC-MS/MS vs. immunoassay) and reference ranges. Deficiency is defined as <30 nmol/L (12 ng/mL), insufficiency as 30–50 nmol/L. Levels above 125 nmol/L may be toxic. Overall evidence is moderate to strong for specific risk groups (elderly, dark skin, limited sun exposure) but not for the general population.