A study published in the Lancet Planetary Health journal suggests that replacing dairy products with plant-based alternatives, such as oat and almond milks, could lead to people missing out on essential vitamins and minerals. Even partial swaps may result in deficiencies in nutrients like iodine, which is crucial for thyroid function and brain health.
Impact on vulnerable groups
The research found that children, teenagers and women appeared to be worst affected by any swap to plant-based milks, yoghurt and cheese. Researchers examined the risks of dropping dairy in favour of plant-based items, including 146 plant-based milks, 76 yoghurts and 67 cheese products.
The team, from the University of Surrey and Queen’s University Belfast, looked at the effect on micronutrient intake for iodine, calcium and vitamins B2 and B12. They also found variations in the extent to which plant-based foods are fortified with added vitamins. Some 12% of plant-based items in the research contained added iodine, 61% had added calcium, 46% had vitamin B12 and 19% had riboflavin (vitamin B2).
Findings on iodine and calcium
The researchers found that even modest replacements of dairy intake with plant-based dairy alternatives, including fortified ones, led to declines in all four micronutrients, but particularly iodine. For example, replacing 20-35% of dairy products with plant-based ones increased the inadequate intake of iodine among girls aged 14-18 from 54% to 65%, and from 32% to 42% in women aged 19-49.
If all dairy was replaced, iodine inadequacy rose to 80% in teenage girls and 72% in boys of the same age. If all dairy was swapped for plant-based products, inadequate calcium intake rose from 30% in the usual diet to 47% among boys aged 14 to 18, and from 54% to 70% among girls the same age. For riboflavin (vitamin B2), if all products were swapped, inadequate intakes in men aged 19-49 rose from 14% to 26%, while the figure was from 29% to 50% for women. There was also a meaningful increase to 39% in this group if only half of usual dairy was swapped for plant-based items.
According to the NHS, calcium is important for building healthy bones and teeth as well as regulating muscle contractions, including heartbeat. Vitamin B12 helps keep the nervous system and blood cells healthy, while B2 is important for skin, eyes and the nervous system.
Calls for fortification
Dr Sarah Bath, associate professor at the University of Surrey and lead author, said: “The UK is particularly vulnerable to iodine insufficiency due to a lack of an iodine fortification policy such as universal salt iodisation, which many other countries have. People may also be unaware of the importance of iodine, which is needed to make thyroid hormones to regulate our metabolism, support healthy growth and brain development.
“Iodine is particularly important during pregnancy, when the requirement increases, but it is also essential prior to pregnancy to ensure that stores are optimised. People are also unaware that dairy products are a major source of iodine, particularly in the UK, and that plant-based alternatives, unless fortified, have a very low iodine content.”
The research included data from more than 3,500 people in the National Diet and Nutrition Survey. The team also used modelling to look at the impact of fortification, including through introducing laws around it. The study suggested mandatory rules to fortify plant-based foods would help increase nutrient intake, although levels of iodine remained inadequate in 59% of teen girls. However, fortifying bread with iodine would lead to a further cut in iodine deficiency.
Dr Katie Nicol, co-author of the study and research fellow at the University of Surrey, said: “Nutrition policy must evolve in tandem with environmental targets however it is important that shifts towards more sustainable diets do not compromise on public health. Fortification of foods is one way that this could be achieved. However, government policy is needed to make this happen.”
Professor Mairead Kiely, from the Cork Centre for Vitamin D and Nutrition Research, said: “Vitamins and minerals that are supplied by animal source foods will need to be replaced in a transition to diets that substantially reduce intakes of these foods and replace them with plant-based alternatives. Plant-based dairy alternatives, unless fortified appropriately, do not contain equivalent amounts of calcium, iodine, riboflavin and vitamin B12 as milk, yoghurt and cheese. Nutrients such as iodine and calcium are already in short supply in the usual diet of people who avoid dairy, and are therefore of public health concern.
“Certain population groups, especially adolescents and women of reproductive age already have low intakes of calcium, iodine and riboflavin. While moderate population-based reductions in dairy are unlikely to cause problems for most people, among those who already consume little, reductions will further reduce the already inadequate intakes of these nutrients.”
Dr Janette Walton, lead investigator for national dietary surveys in Ireland, said: “With dietary guidelines now recommending a large shift from animal-based diets to more plant-based diets in response to meeting global sustainability goals, unintended consequences for the health of teenage girls and young women must be considered.”
Tom Sanders, Professor emeritus of nutrition and dietetics at King’s College London, said a weakness in the study was that “iodine deficiency cannot be reliably predicted from dietary intake records because the iodine content is dependent on the amount in the soil in which plant foods are grown”. He added: “Milk is not naturally high in iodine: the high levels found in milk are because dairy cattle are given ‘salt licks’ that contain supplemental iodine… Seafood is the best natural source of iodine. Iodine deficiency is rare in the UK (as assessed by urinary iodine excretion) because food is now sourced from many countries.”
Emily Angus, senior dietitian at The Vegan Society, said: “To say that ‘replacing dairy in UK diets with the plant-based alternatives currently on sale could reduce the average intake of iodine’ is misleading. The majority of plant-based milk alternatives available to UK consumers are fortified with calcium and vitamin D as a minimum. The Vegan Society has always recommended that people choose fortified dairy alternatives, which, according to the 2025 SACN guidance, are an acceptable and safe alternative to cows’ milk from the age of one.”
Elisa Allen, vice-president of programmes and operations at People for the Ethical Treatment of Animals, said: “The NHS confirms that a well-planned vegan diet can provide the nutrients we need and even the researchers’ own modelling points towards fortification as the solution. It’s time for Britain’s adults to wean.”
