An analysis of 44 non-fortified milk-alternative drinks revealed iodine concentrations of under 2% of that found in conventional cows’ milk. The study examined soya, almond, coconut, oat, rice, hazelnut and hemp beverages and was carried out by the University of Surrey (UoS).
Analysis of the samples was performed by LGC, the UK National Measurement Laboratory and Designated Institute for chemical and bio-measurement.
The researchers found that conventional non-organic milk contained 438 micrograms/ kilo (mcg/kg), whereas the median concentration in the unfortified alternative drinks was 7.3 mcg/kg.
Iodine is widely recognised as essential for normal foetal brain development. Therefore, adequate maternal status is important during pregnancy. Previous research by UoS identified an association between poor maternal iodine status and lower IQ and reading scores in their offspring. A recent Norwegian study covered by NutraIngredients showed a link between inadequate iodine in pregnancy and reduced language and fine motor skills in 3-year olds.
“We wanted to raise awareness of the low concentration of iodine in these drinks,” commented first author Dr. Sarah Bath, Lecturer in Public Health Nutrition at UoS.
“Public awareness of iodine is really poor,” she continued. “Iodine is particularly important during pregnancy and for women planning a pregnancy.
“Many women who are consuming these drinks may not be aware they are missing out on the iodine from cows’ milk.”
Putting into practical terms how little iodine is contained in these milk-alternatives, Margaret Rayman, Professor of Nutritional Medicine at UoS explained, “A glass of a milk-alternative drink would only provide around 2 mcg of iodine which is a very small proportion of the adult recommended iodine intake of 150 mcg/day. In pregnancy, that recommendation goes up to 200 mcg/day."
The only manufacturer who fortified some their milk-alternative drinks was Marks & Spencer. The researchers found iodine levels of 280 mcg/kg, 287 mcg/kg, and 266mcg/kg in their soya, oat and rice drinks respectively.
The study is the first in the UK to examine the iodine content of milk alternatives and is also larger and more comprehensive than any previous US study on this topic.
Other sources of iodine
As part of the objective of raising awareness on iodine, the researchers highlighted the British Dietetic Association (BDA) Iodine Food Fact Sheet as a good source of information on the mineral.
“Iodine is not just found in cows’ milk, but it is the main source in the UK,” explained Bath.
“If avoiding milk and dairy products, consumers need to ensure that they have iodine from other dietary sources, where possible.
“Other good sources [of iodine] are fish, particularly white fish, and eggs,” she advised.
If consumers, such as vegans, are unable to obtain sufficient iodine from dietary sources, then supplementation could be an alternative.
However, Bath emphasised that choice of supplement type was important.
“If people do consider an iodine supplement, it is important that they don’t choose a kelp or seaweed supplement as a source of iodine.”
Supplements sourced from kelp or seaweed can contain excessive (and potentially unsafe) levels of iodine. The BDA Iodine Food Fact Sheet therefore recommends supplements in the form of potassium iodide or potassium iodate.
Organic versus inorganic milk
Consumers may decide to drink organic milk for a variety of perceived health reasons. The researchers found an average concentration of 324 mcg/ kg in organic milk, around 75% of the level in non-organic winter milk.
Seasonal variations occur in the iodine content of milk. Iodine-fortified concentrates are fed to cattle (particularly in the winter months) and iodine-containing disinfectants (used in the UK), increase the iodine content of conventional non-organic milk.
This study used cows’ milk samples drawn in November/ December 2015, reflecting ‘winter’ iodine content. To enable an estimation of an ‘all-year-round’ iodine content in non-organic milk, the researchers also used a median value from their previous 2009 study of 80 cows’ milk samples from the summer.
In this earlier study, the ‘summer’ iodine content was measured at 250 mcg/kg for non-organic milk and 145 mcg/kg for organic milk.
“Organic milk is still a good source of iodine in the UK,” commented Bath.
Source: British Journal of Nutrition
Published online 26th September 2017. DOI: 10.1017/S0007114517002136
“Iodine concentration of milk-alternative drinks available in the UK in comparison with cows’ milk.”
Authors: Sarah C. Bath, Sarah Hill, Heidi Goenaga Infante, Sarah Elghul, Carolina J. Nezianya, Margaret P. Rayman.