Michael S Kramer1,2, Neil Davies3, Emily Oken4, Richard M Martin3,5, Mourad Dahhou1, Xun Zhang1, Seungmi Yang2. 1. Departments of Pediatrics and Epidemiology, Biostatistics and Occupational Health, McGill University Faculty of Medicine, Montreal, Canada. 2. Departments of Epidemiology, Biostatistics and Occupational Health, McGill University Faculty of Medicine, Montreal, Canada. 3. School of Social and Community Medicine, University of Bristol, Bristol, United Kingdom. 4. Division of Chronic Disease Research Across the Lifecourse, Department of Population Medicine, Harvard Medical School and Harvard Pilgrim Health Care Institute, Boston, MA. 5. National Institute for Health Research, Bristol Biomedical Research Center, Bristol, United Kingdom.
Abstract
Background: Previous observational studies have consistently shown slower weight and length gains in infants with prolonged breastfeeding than in those who were formula-fed from birth or breastfed for a shorter duration. These studies inferred that prolonged breastfeeding causes slower growth in infancy. Objective: We compared infant growth associated with ≥12 mo of breastfeeding with a shorter duration of breastfeeding on the basis of 3 different analytic approaches to the same data from a randomized trial: intention-to-treat (ITT; "as randomized"), observational ("as fed"), and instrumental variable (IV; by using randomization as an "instrument" to achieve ≥12 mo of breastfeeding). Design: This was a cluster-randomized trial of a breastfeeding-promotion intervention. Anthropometric measurements were obtained at birth and at 1, 2, 3, 6, 9, and 12 mo. Results: The 3 analytic approaches yielded different results. The ITT approach showed more rapid growth in the first 2 mo among infants randomly assigned to the breastfeeding-promotion intervention than among control infants, with a decreasing difference over the ensuing months and nearly identical weight, length, and body mass index by 12 mo. The observational analysis showed a different trend: higher weight and length in infants who were breastfed ≥12 mo than in those who were breastfed <12 mo during the first 3 mo and no difference by 6 mo, while infants who were breastfed <12 mo showed increasingly higher weight and length from 6 to 12 mo. The IV analysis showed a temporal pattern that was similar to that seen in the ITT analysis, but with larger (and less precise) differences between infants breastfed for ≥12 compared with <12 mo. Conclusions: We observed major differences in experimental (ITT and IV) compared with observational approaches to analyzing data obtained from the same children. These approaches lead to opposite causal inferences about the relation between infant feeding and growth and underline the importance of ensuring that the postulated cause (feeding) temporally precedes its hypothesized effect (growth). This trial is registered at http://www.isrctn.org/ as ISRCTN37687716.
Background: Previous observational studies have consistently shown slower weight and length gains in infants with prolonged breastfeeding than in those who were formula-fed from birth or breastfed for a shorter duration. These studies inferred that prolonged breastfeeding causes slower growth in infancy. Objective: We compared infant growth associated with ≥12 mo of breastfeeding with a shorter duration of breastfeeding on the basis of 3 different analytic approaches to the same data from a randomized trial: intention-to-treat (ITT; "as randomized"), observational ("as fed"), and instrumental variable (IV; by using randomization as an "instrument" to achieve ≥12 mo of breastfeeding). Design: This was a cluster-randomized trial of a breastfeeding-promotion intervention. Anthropometric measurements were obtained at birth and at 1, 2, 3, 6, 9, and 12 mo. Results: The 3 analytic approaches yielded different results. The ITT approach showed more rapid growth in the first 2 mo among infants randomly assigned to the breastfeeding-promotion intervention than among control infants, with a decreasing difference over the ensuing months and nearly identical weight, length, and body mass index by 12 mo. The observational analysis showed a different trend: higher weight and length in infants who were breastfed ≥12 mo than in those who were breastfed <12 mo during the first 3 mo and no difference by 6 mo, while infants who were breastfed <12 mo showed increasingly higher weight and length from 6 to 12 mo. The IV analysis showed a temporal pattern that was similar to that seen in the ITT analysis, but with larger (and less precise) differences between infants breastfed for ≥12 compared with <12 mo. Conclusions: We observed major differences in experimental (ITT and IV) compared with observational approaches to analyzing data obtained from the same children. These approaches lead to opposite causal inferences about the relation between infant feeding and growth and underline the importance of ensuring that the postulated cause (feeding) temporally precedes its hypothesized effect (growth). This trial is registered at http://www.isrctn.org/ as ISRCTN37687716.
Authors: Sarah L Silverberg; Huma Qamar; Farhana K Keya; Shaila S Shanta; M Munirul Islam; Tahmeed Ahmed; Joy Shi; Davidson H Hamer; Stanley Zlotkin; Abdullah Al Mahmud; Daniel E Roth Journal: Curr Dev Nutr Date: 2021-04-30
Authors: Stephanie A Richard; Benjamin J J McCormick; Laura E Murray-Kolb; Crystal L Patil; Ram K Chandyo; Cloupas Mahopo; Bruna L Maciel; Anuradha Bose; Mustafa Mahfuz; Ramya Ambikapathi; Maribel Paredes Olortegui; Laura E Caulfield Journal: Matern Child Nutr Date: 2021-03-04 Impact factor: 3.092