A healthy gut lining is essential for Vitamin D absorption. Conditions like IBS, celiac disease, or even chronic bloating can interfere with nutrient uptake. Vitamin D, being fat-soluble, depends on proper bile flow and enzyme activity from the intestines. A sluggish or inflamed gut might be silently sabotaging the supplement.

Fermented foods, probiotics, and fiber diversity can help strengthen the gut and, in turn, boost Vitamin D effectiveness.