<qa>  What is the name of the serum biomarker that reflects type 1 collagen synthesis inStudies by Diezs group in hypertensive heart disease subjects have identified a reliable serum biomarker that reflects type 1 collagen synthesis in human heart- Carboxy-terminal propeptide of procollagen type 1 PICP15. Serum PICP along with free Matrix metalloproteinases 1 MMP-1 and free Tissue inhibitor of metalloproteinases 1 TIMP 1, as markers of collagen degradation accurately reflect collagen metabolism in the heart15. PICP is released in a 1:1 ratio during the synthesis of type 1 collagen, from its precursor procollagen type 1. Furthermore, peripheral serum PICP accurately reflect amount of collagen type 1 fibres in the heart16 and can therefore be used to monitor the effects of treatment on collagen content of the heart17. However, no studies thus far have shown an effect of vitamin D therapy on changes in ECM composition within the human heart. 