Switching from dairy products to plant-based alternatives could lead to deficiencies in vital micronutrients, especially among young people and women, a study has found.
Even moving partly to vegan alternatives to milk, cheese and yoghurt could lead to falls in iodine, calcium, riboflavin and vitamin B12 if the substitutes, often based on soya, almonds or oats, are not fortified, scientists said.
The greatest concerns surround iodine, a trace element used by the thyroid gland to produce hormones that regulate metabolism and support healthy growth and brain development. More than half of UK teenage girls already have inadequate iodine intake, the researchers said.
Replacing a fifth to a third of dairy intake with plant-based alternatives would lead to prevalence of iodine deficiency rising from 54% to 65% of adolescent girls and from 32% to 42% of women aged 19 to 49 years old, according to modelling based on typical market levels of fortification.
"There are known health effects of iodine deficiency and that's why we want to raise awareness of this," said Dr Sarah Bath, an associate professor in public health nutrition at the University of Surrey. "The population groups that seem to be at risk and have the lowest intakes were the young women and women of childbearing age, and that's the key life stage where iodine is particularly important."
Plant-based alternatives to milk, cheese and yoghurt have grown in popularity, though there are signs some consumers are shifting back.
In the UK, children get about half, and adults about a third, of their total iodine intake from dairy products, but there is no formal requirement for vegan alternatives to be fortified with micronutrients.
The researchers looked at the impact of replacing dairy with plant-based alternatives on the UK market, including 146 non-dairy milks, 76 yoghurts and 67 cheeses. While 61% had added calcium and 46% added vitamin B12, only 19% were fortified with riboflavin and 12% with iodine.
At these levels, the scientists' modelling showed that swapping a third of dairy intake for vegan alternatives led to a 9% to 21% drop in iodine intake, with calcium, riboflavin and vitamin B12 also falling. Switching to 100% non-dairy alternatives led to inadequate levels of iodine reaching 80% in teenage girls and 72% in teenage boys.
Requiring all non-dairy alternatives to be fortified with iodine would prevent average declines, the study found. Adding iodised salt to bread helped reduce the proportion of teenage girls with inadequate iodine intake in the modelled scenarios. The study is published in the Lancet Planetary Health.
Some companies already fortify their dairy substitutes. Niamh Brannelly, the head of nutrition and science communications for Danone in the UK, said its core range of Alpro products was fortified for calcium, iodine and vitamins B2 and B12.
Caroline Orfila Jenkins, a vice-president for science and technology at Oatly, said all its unflavoured, non-organic oat drinks were fortified with nutrients including iodine, calcium, riboflavin and vitamins B12 and D. "This research underlines the importance of appropriate fortification as diets become more plant-based," she said.
Nichola Ludlam-Raine, a registered dietitian and spokesperson for the British Dietetic Association, said the work raised an important population-level concern but did not mean that everyone who switched would become nutrient-deficient because overall diet mattered too.
"For anyone choosing plant-based milk, I'd recommend checking the label and choosing one fortified with iodine, such as Alpro," she said. "Organic drinks aren't fortified with added nutrients, so they're unlikely to provide iodine. White fish such as cod or haddock, as well as eggs and yoghurt and kefir for those who consume them, can also contribute iodine. I wouldn't recommend relying on seaweed or kelp supplements as an iodine source, as the iodine content can vary widely and may be excessive."
