Soil levels of iodine and selenium are low in the UK and much of Europe, and the amounts in plants reflect the amounts in the soil.
In North America iodised salt is used while in most of Europe, including the UK and Ireland, most people get their iodine from dairy products without even realising it has been deliberately added via the cattle feed. Vegans, however, avoid the hidden supplement along with the saturated fat.
Selenium intakes in all sections of the UK population tend to be lower than ideal.
Natural plant foods such as kelp and Brazil nuts can boost intakes of iodine and selenium respectively, though an ideal but not excessive level may be hard to achieve as the amounts contained can vary significantly.