Selenomethionine is the form found in food and is well absorbed and retained by the body, making it the standard choice for everyday use. Methylselenocysteine (SeMSC) is the form found in brassica vegetables and garlic and is handled differently by the body, so some practitioners choose it for specific protocols. Tri-Selenium combines three forms to cover both routes. If you simply want to top up a low dietary intake, selenomethionine is the straightforward option.

The UK reference intake is 55 micrograms a day, and most supplements provide between 50 and 200 micrograms. The safe upper level is 255 micrograms a day from all sources, and this is one mineral where more is not better: intakes well above that over time can cause hair loss, brittle nails and a garlic odour on the breath. Check the label, count any selenium in a multivitamin you take, and stay within the guidance.

Brazil nuts are the richest source, and two or three a day can cover the reference intake, although the amount varies a lot between nuts. Fish, meat, eggs and wholegrains contribute as well. Because UK-grown cereals are lower in selenium than those grown elsewhere, people on plant-based diets who do not eat Brazil nuts are the group most likely to fall short.

The thyroid contains more selenium per gram than any other organ, because selenium-dependent enzymes convert thyroid hormone into its active form. Selenium contributes to normal thyroid function, and it appears alongside iodine in our Thyroid Support Formula for that reason. If you have a diagnosed thyroid condition, discuss any supplement with your doctor, as timing and dose can interact with medication.

Selenium works alongside vitamin E and vitamin C in the body's antioxidant systems, and with iodine and zinc in thyroid function. It does not compete for absorption in the way calcium, iron and zinc do, so it can be taken with meals and other supplements without special timing. Our ionic liquid suits anyone who wants to start low and build up gradually.