Quantification of the bioavailability of riboflavin from foods by use of stable-isotope labels and kinetic modeling

Abstract

A large fraction of newly absorbed riboflavin is removed by the liver on "first pass." The plasma appearance method therefore underestimates riboflavin bioavailability and should not be used to estimate riboflavin bioavailability from foodstuffs. Urinary monitoring suggests that riboflavin from spinach is as bioavailable as is riboflavin from milk.

Dietary Reference Values for riboflavin

“…() using oral riboflavin doses, which calculated the maximum amount of riboflavin that can be absorbed as about 27 mg. IOM () based its discussion on bioavailability of riboflavin on Zempleni et al. (), which showed that absorption from the gut lumen was 95% complete within 4.4 h. In a study in 20 healthy women using 13 C‐labelled riboflavin in semiskimmed milk or 15 N‐labelled free riboflavin and FMN in spinach soup and urinary monitoring, there was no significant difference in true absorption between the spinach meal and the milk meal (Dainty et al., ).…”

Spinach and Health

“…Spinach is a superior supplier of vita min K, vitamin A, manganese, magnesium, fo lic acid, iron, vitamin C, vitamin B2, and potassium, and it includes a lot of dietary fiber, vitamin B6, vitamin E, and omega-3 fatty acids [25][26][27][28], which are essential for the main tenance, improvement, and regulation of human tissues. In addition, spinach includes major antioxidants of carotenoids and polyphenols (i.e.…”

Recent progress in stable isotope methods for assessing vitamin metabolism

“…Bluck, W.A. Coward, unpublished data); riboflavin from 15 N labelled spinach [27]; and vitamin K -2 H labelled Collard greens [28] and broccoli [29]. Intrinsic labelling does not produce substrates labelled at specific sites; the labelling pattern is quasirandom.…”

“…It must be strongly emphasized that the adequate description of the observed data does not on its own confer legitimacy on any particular model; rather the model must also have some physiological basis. The various models that have been proposed for vitamin A metabolism have been reviewed [31], and models proposed for riboflavin [27], folate [32], vitamin C [5] and vitamin K; [23 ] In general, the fat-soluble vitamins require a more complex model to fully account for their uptake and tissue distribution. Once absorbed, these vitamins (or their precursors) are transported to the liver in chylomicrons, and then rereleased into the bloodstream bound in the lipoprotein fractions.…”

“…It appears that when a labelled oral test dose is given, there is a concurrent release of preexisting unlabelled material from tissues into the plasma. The source of this efflux is not understood, but there is evidence that it may be hepatic in origin, and similar processes may occur for vitamins B 2 [27] and B 6 [39], and possibly all watersoluble vitamins. …”