Calcium absorbability from spinach

Abstract

The absorbability of calcium from spinach was compared with the absorbability of Ca from milk in 13 healthy adults in a randomized cross-over design in which the test meal of either milk or spinach had 200 mg of Ca labeled with 45Ca. Absorption was measured by the standard double-isotope method in which both the test food and the miscible Ca pool are labeled with different Ca tracers. Measurement of both Ca and oxalate in our test spinach revealed a very slight stoichiometric excess of oxalate; hence it is likely that all of the spinach Ca was effectively bound. Absorption was higher from milk in every case, with the mean absorption from milk averaging 27.6% and from spinach, 5.1%. The mean within-subject difference between Ca absorption from milk and from spinach was 22.5 +/- 9.5% (P less than 0.0001). These results conclusively establish that spinach Ca is much less readily available than milk Ca.

Invited review: Dairy intake and bone health: A viewpoint from the state of the art

“…Gueguen and Pontillart (2000) reviewed the literature comparing the bioavailability of calcium in different foods. In humans, the calcium in milk and several milk derivatives (yogurts, cheeses, chocolate) is not more efficiently used than calcium salts (carbonate, gluconolactate, citramalate, lactate, acetate, and citrate) but is much better absorbed than the calcium in spinach or water cress, as these plants have high oxalate content, inhibiting intestinal absorption of calcium (Weaver et al, 1987;Heaney et al, 1988). Studies in rats show that calcium in whey is as efficiently absorbed and utilized for bone mineralization as that bound to CN.…”

Nutritional impact of elevated calcium transport activity in carrots

“…Many vegetables contain antinutritients that can interfere with calcium absorption in the gut (18). These compounds can bind the calcium freely, and some plants also can bind calcium during the growth process (18)(19)(20).…”

“…Many vegetables contain antinutritients that can interfere with calcium absorption in the gut (18). These compounds can bind the calcium freely, and some plants also can bind calcium during the growth process (18)(19)(20). In the case of spinach, a poor source of bioavailable calcium, the incorporation of a 45 Ca tracer in bone is reduced by 50% in the intrinsically labeled diets compared with the extrinsic diets when fed to rats or mice (14,15).…”

Oxalic acid does not influence nonhaem iron absorption in humans: a comparison of kale and spinach meals

“…OA is a well-known inhibitor of calcium absorption in humans (Heaney et al, 1988;Heaney and Weaver, 1989), and has been reported to decrease zinc (Kelsay and Prather, 1983) and magnesium (Bohn, 2003) absorption. Formation of insoluble oxalate complexes is the most likely explanation based on the observation that addition of calcium decreased OA absorption from the diet in a dose-dependent fashion (von Unruh et al, 2004).…”