Mapping Iodine Sources for Human Nutrition in Portugal Considering Geography, Seasonality, and Processing: Milk and Plant-Based Milk Alternatives

Abstract

Background: Iodine is a micronutrient essential for the synthesis of thyroid hormones and crucial throughout life. Milk is potentially one of the major contributors to iodine intake in many countries, including Portugal, due to its consumption patterns. Objectives: This study characterizes iodine content seasonality in milk and plant-based milk alternatives commercially available in Portugal. Results: Milk products representing summer and winter seasonal pastures and plant-based alternatives were obtained from major Portuguese supermarkets. Iodine was quantified by the Sandell-Kolthoff reaction in 146 winter and 142 summer milk products, as well as in 128 plant-based alternatives. Cow's milk contained relevant iodine levels (Md = 19.9, IQR = 9.9 mu g/100 mL), with no influence of thermal processing, fat or lactose content, season, or being organic and/or from pasture. However, regional differences were observed. The iodine concentration in plant-based drinks was residual, except for four fortified products. Conclusions: This study provides evidence that milk is still a relevant source of iodine in Portugal, whereas most plant-based alternatives provide negligible iodine, unless fortified. Given shifts towards plant-based diets, monitoring iodine sources and adjusting health policies to fulfil nutritional requirements are pivotal to ensure iodine adequacy.