Experts query findings of recent paper in BJN highlighting nutritional benefits of organic milk
Two sets of scientists have written commentaries in the latest issue of the British Journal of Nutrition querying the findings of a recent article published in the same journal by scientists from Newcastle University that suggested potential nutritional benefits of consuming organic milk.
Analysing data from around the world, the original article by Dr Dominika Średnicka-Tober et al. reviewed 196 papers on milk and found differences between organic and conventional milk, especially in terms of fatty acid composition, and the concentrations of certain minerals and vitamins including iron, Vitamin E and some carotenoids.
Publishing their findings in the British Journal of Nutrition in March 2016, the Newcastle team emphasised that the data showed a switch to organic milk would go some way towards increasing our intake of nutritionally important fatty acids based on the observation that organic milk contains around 50% more beneficial omega-3 fatty acids than conventionally produced milk.
However, experts from the University of Surrey and the University of Reading have written two separate commentaries in the May 2016 issue of the British Journal of Nutrition questioning some of these findings, which were widely reported by the mainstream media earlier this year.
In their commentary, Dr Sarah Bath and Professor Margaret Rayman from the University of Surrey’s Faculty of Health and Medical Sciences call into question the emphasis placed on the fatty acid composition of organic milk in the original article and in subsequent media reports about the nutritional benefits of organic milk. In fact, they suggest that the most significant difference revealed in the article between organic and conventional milk in terms of their contribution to meeting nutritional requirements is its iodine content.
Dr Bath and Prof Rayman report that milk is the single biggest contributor to iodine intake in many countries, and particularly in the UK where iodised salt is rarely used, whereas milk is a relatively inconsequential source of fatty acids in our daily diets. Their analysis of data from the original article found that drinking a glass of organic milk would provide 13.3% less of the daily recommended intake of iodine for an adult than drinking a glass of non-organic milk. These findings are of particular importance in the UK, they write, because iodine deficiency is prevalent in certain population groups, notably in pregnant women and women of childbearing age which can have significant implications for fetal brain development.
“The finding of lower iodine content in organic milk is an important message for consumers to hear,” they write, adding that this message must not be lost when promoting organic milk. “Consumers need to be directed to alternative dietary sources to ensure they have adequate iodine intake overall.”
“As nutritional differences are one of the factors that may influence the purchase of organic milk,” they conclude, “it is important that scientists ensure that consumers are given a balanced picture so that they can weigh up the potential benefits and disadvantages of its consumption.”
A second commentary by Professors Ian Givens and Julie Lovegrove from the University of Reading raise similar concerns about the findings of the original article by the Newcastle team.
“We have concerns over how the data have been presented, which has led to considerable misinterpretation by the media,” they write.
The experts from Reading emphasise that it is important to assess and discuss the impact of the observed differences in the context of the typical whole diet. And their analysis of the data in the original article leads them to very different conclusions from the original article:
“Overall differences in milk fatty acids in organic v. conventional systems are extremely small when examined in the context of total diets and would have very limited contribution to nutrition or health,” they write. “And the differences are because of the diet of the cow and not specifically because of organic production.”
Read the original Open Access paper in full:
‘Higher PUFA and n-3 PUFA, conjugated linoleic acid, α-tocopherol and iron, but lower iodine and selenium concentrations in organic milk: a systematic literature review and meta- and redundancy analyses.’ Dominika Średnicka-Tober et al. British Journal of Nutrition.
Read the two invited free to access commentaries:
‘Trace element concentration in organic and conventional milk: what are the nutritional implications of the recently reported differences?’ Sarah C. Bath and Margaret P. Rayman British Journal of Nutrition.
Higher PUFA and n-3 PUFA, conjugated linoleic acid, α-tocopherol and iron, but lower iodine and selenium concentrations in organic milk: a systematic literature review and meta- and redundancy analyses. D. I. Givens and J. A. Lovegrove. British Journal of Nutrition.