“…The investigated vitamin D metabolites were 25(OH)D (11 studies) [14,[17][18][19]21,[23][24][25][26]28,31], 1,25(OH) 2 D (6 studies) [14,17,24,25,27,31], and 24,25(OH) 2 D (2 studies) [24,31]. Six studies did not report the investigated metabolite [15,16,20,22,29,30], declaring that they analyzed "serum vitamin D". The other concomitant and most frequently analyzed parameters were bone mineral density (nine studies) [14,16,17,[19][20][21]23,26,30], serum estradiol level (three studies) [14,17,25] and other bone metabolism biomarkers, as part of the studies focused on bone density and risk of osteoporosis after gastric cancer surgery with vitamin D and its metabolites evaluated only as indicators.…”