Partial Dairy Swaps Spike Iodine Deficiency Risk in Teens

Substituting just a fraction of daily dairy consumption with plant-based alternatives can sharply elevate the risk of nutrient deficiencies, particularly for young women. Data from the University of Surrey indicates that swapping 20% to 35% of milk, yogurt, and cheese products causes the estimated prevalence of inadequate iodine intake among adolescent girls to jump from 54% to 65%. For women aged 19 to 49, this figure rises from 32% to 42%.

Impact on Essential Micronutrients

The research highlights significant reductions not only in iodine but also in calcium, riboflavin, and vitamin B12 levels when dairy is partially replaced. While these shortfalls are concerning, the study suggests that fortifying plant-based alternatives and other food staples could mitigate these nutritional gaps. The findings underscore the complexity of aligning dietary shifts with public health requirements.

Study Methodology and Scope

This represents the first UK-based analysis of its kind, conducted by researchers at the University of Surrey and Queen’s University Belfast. The team examined dietary data from over 3,500 participants ranging in age from 18 months to 100 years. Using the National Diet and Nutrition Survey, they modeled the effects of replacing traditional dairy items with commercially available plant-based substitutes on four key micronutrients.

Dr Katie Nicol, a research fellow at the University of Surrey and co-author, noted the growing emphasis on plant-based diets due to environmental sustainability concerns. She emphasized the need to determine if these alternatives serve as true "like-for-like" replacements for dairy-derived micronutrients. This issue is especially critical for vulnerable groups, such as young children and adolescent females, who face higher risks of deficiency that could impact overall health.

Iodine Vulnerability in the UK

Iodine emerged as the most affected nutrient in the modeling scenarios. When researchers simulated a complete replacement of dairy with current plant-based options, inadequate iodine intake reached 80% among adolescent girls and 72% among adolescent boys. These figures reflect modeled dietary inadequacy rather than confirmed clinical deficiencies.

Dr Sarah Bath, associate professor at the University of Surrey and lead author, pointed out that the UK lacks an iodine fortification policy, such as universal salt iodization, which exists in many other nations. She explained that iodine is vital for producing thyroid hormones, regulating metabolism, and supporting growth and brain development. Requirements increase significantly before and during pregnancy, yet many people remain unaware that dairy is a major iodine source in the UK, while unfortified plant-based alternatives contain very little.

Policy Solutions and Fortification

Mandatory fortification of plant-based dairy alternatives appears capable of preventing declines in micronutrient intake. However, even with fortified alternatives, approximately 59% of adolescent girls would still experience inadequate iodine levels. Introducing iodine into bread reduced this percentage to 37%, indicating that combining multiple fortification strategies yields better results.

Dr Anne Nugent from Queen’s University Belfast detailed the analytical process, which involved identifying all foods containing milk, cheese, and yogurt in the national survey. The team then substituted these items with equal weights of plant-based alternatives, ensuring each identified product had an equal chance of selection to account for varying nutritional compositions. They tested whether specific fortification options could offset shortfalls without causing excessive nutrient intake.

Dr Nicol stressed that nutrition policy must evolve alongside environmental targets. She argued that shifts toward sustainable diets should not compromise public health, suggesting that government-led food fortification policies are essential to achieve this balance.

The study, titled “The impact of replacing dairy products with plant-based dairy alternatives on iodine and other micronutrients: a modelling study and evaluation of policy options to support population intake,” was authored by Katie Nicol, Anne P Nugent, Jayne V Woodside, Kathryn H Hart, and Sarah C Bath. It was published in The Lancet Planetary Health (DOI: 10.1016/j.lanplh.2026.101515).