1. Nutrition Innovation Centre for food and HEalth (NICHE)
‘Global Excellence in Nutrition Research & Education’
Factors influencing iodine and selenium concentrations of cow’s milk in Northern Ireland
A.J. Yeates1, S.M.O’Kane1, L.K.Pourshahidi1, M.S. Mulhern1 and J.J. Strain1
1Nutrition Innovation Centre for Food and Health (NICHE), Ulster University, Coleraine, BT52 1SA
Introduction
Cow’s milk is the major dietary source of iodine for UK consumers(1)
Iodine, together with selenium, are required for thyroid hormone synthesis and are thus important for growth, metabolism and neurodevelopment(2)
Concentrations of iodine and selenium are known to be highly variable within cow’s milk(3)
Such variability could influence the contribution of milk to total dietary intakes of iodine and selenium
Results
Year-round mean (SD) concentrations of iodine and selenium were 475 (63.5) µg/kg and 17.8 (2.7) µg/kg
Results showed iodine, but not selenium, concentrations to differ significantly by season
Neither iodine nor selenium concentrations differed by fat class (whole, semi-skimmed or skimmed) or between raw and pasteurised milk
Table 1. Mean (SD) iodine and selenium concentrations according to milk fat class, pasteurisation and season
† Mean of skimmed, semi-skimmed and whole milk samples
‡ Samples were collected pre-pasteurisation and pre-homogenisation
a,b,c values within a column with different superscript letters represent significance (P< 0.05).
Iodine (µg/kg)
Selenium (µg/kg)
Milk type n
Mean SD P
Pasteurised† 36
 475.9
63.5 
 0.275
17.76
2.73
0.438
Raw‡ 12
 451.7
 71.9
18.44
2.04
Skimmed
 472.6
 76.0
18.45
2.03
0.545
Semi-Skimmed
 466.6
 62.6
 0.696
17.61
3.31
Whole
 488.5
 53.3
17.22
2.8
Winter 9
498.1a,b
30.6
<0.001
17.8
0.18
Spring
534.3a
53.7
18.8
2.4
Summer
437.4b,c
48.9
16.1
2.5
Autumn
433.6c
57.8
18.4
2.9
Objective
To analyse iodine and selenium concentrations in NI milk over a full year
To examine the effect of milk fat class, pasteurisation and season on iodine and selenium concentrations
Methods
Milk Collection
Raw & pasteurised (semi-skimmed, skimmed and whole) milk samples collected weekly from two large creameries
April May 2014; n=376 samples
Samples stored at -20oC at Ulster University
Milk Digestion
Iodine: 5% TMAH + Oven digestion (90oC 3 hrs)
Selenium: Nitric acid + Microwave digestion → 30% H2O2 + H20
Internal standard: Tellurium
Milk Analysis
Milk digests analysed by LGC Standards by ICP-QQQ-MS (Agilent)
Quality control ensured with external calibration & use of certified reference material for which mean recoveries for iodine and selenium were 97% and 108%
Statistical Analysis
Weekly milks pooled → monthly samples (n=48) → seasonal samples of each type (n=12)
Independent samples t-test & One way ANOVA used to compare differences by season, fat class and pasteurization (SPSS v22.0)
Conclusions
Season is the major factor influencing variation in iodine concentrations in cow’s milk; likely reflecting the animal diet
Overall, iodine concentrations of NI milk are higher than previous UK(3) and Ireland reports (4)
Further research is required to understand factors contributing to seasonal variability in iodine concentrations
Acknowledgments
We acknowledge the LGC Group for the analysis of milks in this study and the Dairy Council for Northern Ireland for their support in the studentship
This work was supported by funding from the Department of Agriculture, Environment and Rural Affairs (DAERA) through a postgraduate studentship (2013 – 2016)
References
Bates et al (2015) National Diet and Nutrition Survey Results of the Rolling Programme. Food Standards Agency/ Public Health Agency
Bath et al (2015) Lancet 382, 337-7
Payling et al (2015) Food Chemistry 178,
Food Safety Authority of Ireland (FSAI) Total Diet Study. Dublin:FSAI (2011)
Web: