However, two other small US studies have failed to confirm such findings (34,38).
The functions of other selenoproteins are less well characterised but recent work has shown that selenoproteins H, L, T and W (Sel H, Sel L, Sel T and Sel W) and the 15 k Da selenoprotein are members of a novel family of selenoproteins that contain a thioredoxin-like redox fold (6).
Sel S, Sel N, 15 k Da selenoprotein and Sel M are endoplasmic reticulum (ER) proteins that appear involved in redox balance and the unfolded protein response (6,15–18).
The second stimulus was the outcome of the randomised controlled National Prevention of Cancer (NPC) trial carried out in the USA.
In this trial, 1000 subjects with a history of non-melanoma skin cancer were given a Se supplement (Se-enriched yeast; 200 μg/day) or placebo for 4.5 years and then followed up for a further 6.5 years.
Thus, for example, GPx1 protein and m RNA levels are more sensitive to Se deficiency that GPx4 in many tissues, GPx4 more sensitive to deficiency in the liver than the heart and deiodinase activity is less sensitive to Se deficiency in the thyroid than in the liver (19).