Calcium bioavailability from high oxalate vegetables: Chinese vegetables, sweet potatoes and rhubarb

Absorption of calcium from high calcium vegetables endogenously labeled with ⁴⁵Ca was studied in premenopausal women using a randomized cross over design. Chinese (C.) vegetables are a major source of calcium, but the bioavailability is unknown and likely affected by the oxalic acid content. Calcium absorption from Chinese vegetables, sweet potatoes, and rhubarb, was compared to milk at the same calcium level for calculation of an absorption index. Calcium absorption generally reflected oxalic acid content. Calcium absorption index (X ± SEM) was least for C spinach (0.257 ± 0.0228) and rhubarb (0.235 ± 0.0233), intermediate for sweet potatoes (0.423 ± 0.0255), and highest for C. mustard greens (1097 ± 0.0532) and C. cabbage flower leaves (1.097 ± 0.0532).