Relative folate bioavailability from diets containing human, bovine and goat milk

The present study was designed to determine the relative folate bioavailability from diets containing human, bovine or goat milk and the relative sensitivity of various response criteria used in assessing folate bioavailability. Following a 12-wk depletion period, 16 groups of male rats (n = 5/group) were fed experimental diets with or without 20% milk solids and graded levels of folic acid for 4 wk. Total folates were measured in plasma, erythrocytes, liver and kidney. Bioavailability of dietary folate was determined using slope-ratio statistics. Plasma response was found to be the most sensitive indicator of folate bioavailability based on steepness of slope, goodness of fit (r = 0.96, P less than 0.01) and linearity of response over the entire range of folate intakes. Kidney folate concentration also showed a significant linear relationship to total folate intake (r = 0.69, P less than 0.01). Liver and erythrocyte folate concentrations were not correlated with folate intake (r = 0.33 and r = 0.22, respectively). Using plasma folate as the response criterion, dietary incorporation of human milk significantly enhanced folate bioavailability by 75% (P less than 0.01). With kidney as the response tissue, folate bioavailability from diets containing human and bovine milk was significantly enhanced over milk-free diets. These results show that incorporation of human or bovine milk into diets enhances folate bioavailability and that plasma and kidney folate concentrations are sensitive and specific indicators of folate bioavailability.