Availability of food folate in humans

The aim of our study was to determine whether the area-under-the-plasma-response-curve method with the positive area (AUC+) as primary analysis variable is suitable to evaluate the availability of food folate in humans. Healthy volunteers (n = 20) received four test meals in a randomized, four-period cross-over design as follows: meal A, 600 g spinach; meal B, 300 g spinach; meal C, 0.4 mg folic acid in water; meal D, folate-free control meal. Blood samples were drawn before administration of the test meals and up to 10 h postprandially. Plasma folate was significantly increased for up to 6 h after uptake of spinach and folic acid (P < 0.007), whereas the response curve after the control meal decreased slightly but significantly (P < 0.007). To calculate the net increase of plasma folate, the values were corrected by the individual predose concentrations. The AUC+ was calculated with these corrected values. The mean AUC+ was highest after consumption of meal A (71.2 +/- 24.0 h x nmol/L) followed by meal C (61.8 +/- 23.8 h x nmol/L) and meal B (41.4 +/- 19.4 h x nmol/L). The AUC+ after meal B was significantly lower than after the other two meals (P < 0.05). The results suggest that the AUC method with multiple blood sampling is useful for assessing the availability of food folate in humans.