Reduced plasma half-life of radio-labelled 25-hydroxyvitamin D3in subjects receiving a high-fibre diet

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Abstract
1. The plasma disappearance of3H-labelled 25-hydroxyvitamin D3(25(OH)D3) was studied in healthy volunteers on normal and high-fibre diets, using3H-labelled tracer doses given intravenously.2. The mean (±SEM) plasma half-life in the high-fibre-diet group was 19·2±1·7d, which was significantly shorter than in the group on normal diets (27·5±2·1 d,P< 0·02).3. This finding suggests that a high-fibre diet leads to enhanced elimination of 25(OH)D3by an action within the intestinal lumen. This may involve interference with an enterohepatic circulation of the metabolite, perhaps by binding of 25(OH)D3to dietary fibre.4. The reduced plasma half-life of3H-labelled 25(OH)D3associated with a high-fibre diet may explain the development of vitamin D deficiency in Asian immigrants with normal exposure to u.v. light.