Bioavailability of Zinc from milk and rice using a stable isotope method

Zinc deficiency is widespread globally. Some estimates indicate that 20% of the
total world population has some degree of zinc deficiency. Zinc is one of the
many essential nutrients found in milk. With a concentration of ~0.4 mg Zn per
100 g of milk, it forms an important source of Zn in dairy consuming
populations such as in the Netherlands. There are indications in the literature
that milk could enhance Zn absorption from plant-based foods, but this needs to
be confirmed. To our knowledge, information on zinc absorption from regular
dairy products in human subjects is scarce, as well as information on the
effect of enhancing factors (proteins) in milk.

Study I: To assess the bioavailability of Zinc from full cream UHT milk,
fortified full cream UHT milk, a supplement, and raw milk.

Study II: To assess the potential enhancing effect of milk on Zn absorption
from intrinsically labelled rice (as a model for a phytate containing staple
food)

Open, partially randomized, cross-over study.

Study I: Intake of
1) Two times 400 ml full cream *Langlekker* milk, extrinsically labelled with 1
mg of 67Zn, consumed with a 1-hr interval;
2) Two times 200 ml Zn-fortified full cream *Langlekker* milk + 200 mL water
(to keep volume the same), extrinsically labeled with 1 mg of 67Zn , consumed
with a 1-hr interval;
3) Two times 400 ml water + Zn supplement, extrinsically labelled with 1 mg of
67Zn, consumed with a 1-hr interval.
4) Two times 400 ml raw milk

Study II: Intake of
1) Two times 45 g intrinsically 67Zn labelled rice + 300 mL of full cream
*Langlekker* milk , consumed with a 1-hr interval;
2) Two times 45 g intrinsically 67Zn labelled rice + 300 mL of Zn fortified
water, consumed with a 1-hr interval.

Each meal will contain ~ 4 mg of Zn. In between meals, subjects will receive an
intravenous dose of 0.2 mg 70Zn, dissolved in 10 mL saline.

The risks associated with participation can be considered minimal. The
intervention products and stable isotopes are safe for human use; apart from
possible gastrointestinal discomfort from consuming 800 mL of milk, and no side
effects are expected for the subjects (except rare complications of
venepuncture and intravenous injection such as bleeding and bruising). The
burden consists of 4 (study I) or 2 (study II) test days; on each test day the
subjects consume one of the test products, undergo a venepuncture and an
intravenous injection. Four days later subjects will collect a urine sample.
The subjects will not experience any health benefit from participation. Similar
studies on Zn bioavailability from intrinsically labelled rice and millet have
been performed in the past four years in a collaborative project between WU and
ETH Zürich at study sites in China, Switzerland and Burkina Faso. Therefore,
ample experience with these stable isotope studies is at hand.