Myths vs facts: Vitamin D 25-OH and weight loss

The claim that vitamin D (25-OH) directly causes weight loss is a myth. Large randomized controlled trials (RCTs) show no significant effect of vitamin D supplementation on weight reduction. The observed correlation between low vitamin D levels and obesity is largely reverse causation: adipose tissue sequesters vitamin D, lowering blood levels. However, vitamin D deficiency can impair overall health (bone, immune, mood), which may indirectly affect exercise capacity and motivation. MyBody-X tests measure 25-OH levels accurately, but marketing it as a weight-loss tool is not evidence-based. Supplementation is only recommended for confirmed deficiency, not for weight loss. Evidence: human-moderate (RCTs show no weight loss benefit, but associations are well-documented).