Folate bioavailability from milk-containing diets is affected by altered intestinal biosynthesis of folate in rats

This study was designed to assess the effect of succinylsulfathiazole on the apparent bioavailability of folate added to milk-containing diets. We also evaluated the impact of milk type on the relative bioavailability (bioavailability) of folate following pasteurization (62.5 degrees C, 30 min) and on the bioavailability of folic acid (PteGlu) vs. pteroylhexa-gamma-L-glutamic acid (PteGlu6). Following folate depletion (5 wk), 108 rats (six per group) were fed for 4 wk diets with or without 20 g milk solids/100 g diet and containing PteGlu, PteGlu + 5 g/kg succinylsulfathiazole, or PteGlu6. Folate bioavailability was determined using plasma folate concentration and a standard curve generated from rats fed milk-free diets with graded levels of PteGlu. The PteGlu and PteGlu6 bioavailability from human milk-containing diets was twice that of diets containing cow or goat milk (P < 0.05). Incorporation of a sulfa drug into diets containing human or cow milk reduced PteGlu bioavailability by one half (P < 0.05). Further, the values for bioavailability of PteGlu from diets containing human or goat milk no longer differed (0.86 and 0.75, respectively), and bioavailabilities from human milk- and goat milk-containing diets were greater than that of the cow-milk-containing diet (0.54) (P < 0.05). Pasteurization of milk did not influence folate bioavailability. The bioavailability of PteGlu6 was 49-71% that of PteGlu (P < 0.05). In summary, milk type differentially affects intestinal folate biosynthesis, and the superior folate bioavailability from human milk-containing diets is due in part to enhanced intestinal biosynthesis of folate.