Case-control study of breast milk calcium in mothers of children with and without nutritional rickets

Aim: Despite similarly low calcium intakes and normal vitamin D status, only some Nigerian children develop nutritional rickets. We hypothesized that mothers with children who had developed rickets might have lower breast-milk calcium concentration than mothers with normal children and compared the breast-milk calcium concentration of mothers who had had children with rickets with those who had not (controls). Methods: We collected breast milk from 35 Nigerian mothers who had previously had children with nutritional rickets. For each case mother, we collected breast milk from three matched control mothers at the same stage of lactation (9/4 weeks) who had had no children with rickets. Data were collected about parity, stage of lactation, and the infant's intake. The mother's bone density was measured. Results: The mean breast milk calcium concentration of mothers of children with rickets (4.30 +/- 1.24 mmol/L) was less than that of control mothers (4.65 +/- 1.03 mmol/L; P = 0.034 in multivariate regression controlling for duration of lactation and resumption of menses). Forearm bone mineral content was significantly related to breast milk calcium concentration (r = 0.20) after adjusting for height, weight, and bone area (P = 0.028).