“Optimising iodine intake is therefore challenging, since globally there seems to be as much concern about excessive rather than inadequate intake.”

In the USA, China, Brazil and many European countries, where Iodine fortified salt is widely used, elevated levels of iodine in milk may increase the risk of excessive intake for individuals with high dairy consumption. For this reason the European Food Safety Authority (EFSA) has proposed a reduction in the permitted level of iodine in cattle feed from 5 to 2 mg iodine per kg of feed.

However, in the UK, where iodized salt is not widely available, the population relies more on milk and dairy products for adequate iodine supply. National Diet and Nutrition Survey data (NDNS) suggest that milk and dairy products supply between 31-52% of iodine in the UK diet.

The daily recommended intake of iodine in the UK is 140 µg/day and just over half comes from dietary sources other than milk/dairy products. Based on results from the study, half a litre of milk would provide 53% of and 88% of the daily recommended intake from organic and conventional milk respectively. However, pregnant and breastfeeding women have a higher iodine requirement (250 µg/day) and are therefore more at risk of iodine deficiency, which could affect neurological development in babies.

Further evidence of the health benefits of organic food

The work builds on a previous study by the team - involving experts from the UK, US, France, Italy, Switzerland, Norway and Poland - investigating the composition of organic and conventionally-grown crops.

This previous study - also published in the British Journal of Nutrition - showed that organic crops and crop-based foods are up to 60% higher in a number of key antioxidants than conventionally-grown crops and contained less of the toxic metal cadmium.

“We have shown without doubt there are composition differences between organic and conventional food. Taken together, the three studies on crops, meat and milk suggest that a switch to organic fruit, vegetables, meat and dairy products would provide significantly higher amounts of dietary antioxidants and omega-3 fatty acids,” concludes Professor Leifert.

“We need substantially more, well designed studies and surveys before we can accurately estimate composition differences in meat from different farm animals and for many nutritionally important compounds (vitamins, minerals, toxic metal and pesticide residues), as there is currently too little data to make comparisons.

“However, the fact that there are now several mother and child cohort studies linking organic food consumption to positive health impacts shows why it is important to further investigate the impact of the way we produce our food on human health.

The authors highlight that only a small number of studies have been carried out comparing organic and non-organic meat, and that even significant results may still carry a high level of uncertainty.

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Carlo Leifert
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Newcastle University