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expert reaction to study looking at feeding practices and metal concentrations in children’s blood

A study published in JAMA Network Open looks at infant feeding practices and metal concentrations in the blood. 


Prof Andy Smith, MRC Toxicology Unit, Cambridge, said:

“The paper by Smith et al in JAMA Network Open describes the comparison of 7 essential metals and 8 nonessential metals in the red blood cells of children approximately 3 years of age, and categorised whether over their first 6 months they had been totally breast fed, weaned from breast feeding or were mixed.  The results demonstrate the approach that could be taken to associate mothers’ milk or other sources of postnatal metal intake with early childhood erythrocyte blood levels.  However, this study itself does not provide any conclusions as to associations with health outcomes or maternal backgrounds although ages, ethnicity, education and household income were reported.”


Prof Andrew Meharg, Professor of Biological Sciences, Queen’s University Belfast, said:

“This is a really weak piece of research.  It is quite a brief paper and the details of the experimental design are not clear.

“The data appear to be statistically negative – i.e. no significant differences are reported – but then no stats are reported beyond confidence intervals.  Some of the elemental analysis is questionable without full analytical details, including analysis quality assurance/quality control.  Total arsenic reporting is irrelevant – it is the type of arsenic present that is all important – if breast feeding mothers had higher fish consumption this would be enough to explain the results as fish are high in a safe form of arsenic, arsenobetaine.

“I’m surprised this study got through peer review.

“We know from other data that there are many positive outcomes from breast feeding.  This study should not be taken as meaning that breast feeding is harmful.”



‘Infant Feeding Practices and Metal Concentrations in Children’s Blood’ by Anna R. Smith et al. was published in JAMA Network Open at 16:00 UK time on Monday 18 December 2023.

DOI: 10.1001/jamanetworkopen.2023.48230



Declared interests

Prof Andy Smith: “I have no conflicts of interest.”

Prof Andrew Meharg: “I have no conflicts of interest.”

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