Is Vitamin D 25-OH useful for Stress?

Vitamin D 25-OH (25-hydroxyvitamin D) is the standard biomarker for vitamin D status. Observational studies link low levels to higher perceived stress, anxiety, and mood disturbances. However, evidence from randomized controlled trials (RCTs) is mixed: supplementation does not consistently reduce stress in non-deficient individuals. Vitamin D 25-OH is not a direct stress test; it reflects overall vitamin D sufficiency, which may indirectly influence stress pathways (e.g., via immune modulation, neurotransmitter synthesis). Consumer lab tests (e.g., MyBody-X) can measure this marker, but results must be interpreted cautiously. A deficiency should be corrected, but expecting a stress-relief effect from vitamin D alone is not strongly supported by current evidence. The effect size is small and context-dependent. Evidence grade: human-moderate (observational + limited RCT support). Caveat: no validated cutoff for stress; clinical assessment remains essential.