To investigate whether the recommended dietary intake of Ca in anaemic infants compromises the expected Hb response, via home fortification with a new Ca- and Fe-containing Sprinkles™ micronutrient powder (MNP).

A double-blind, randomized controlled, 2-month trial was conducted in Bangladesh. Infants were randomized to one of two MNP intervention groups containing Fe and other micronutrients, with or without Ca. Hb, anthropometrics and dietary intake were measured pre- and post-intervention while family demographics were collected at baseline.

Twenty-six rural villages in the Kaliganj sub-district of Gazipur, Bangladesh.

One hundred infants aged 6–11 months.

A significant increase in Hb (MNP, 13·3 (sd 12·6) g/l v. Ca-MNP, 7·6 (sd 11·6) g/l; P < 0·0001) was noted in infants from both groups. However, infants receiving MNP without Ca had a significantly higher end-point Hb concentration (P = 0·024) and rate of anaemia recovery (P = 0·008). Infants receiving MNP with Ca were more likely to remain anaemic (OR 3·2; 95 % CI 1·4, 7·5). Groups did not differ in dietary intake or demographic and anthropometric indicators.

Although both groups showed significant improvement in Hb status, the nutrient–nutrient interaction between Fe and Ca may have diminished the Hb response in infants receiving the Ca-containing MNP.