Vitamin E deficiency, including in cystic fibrosis, chronic cholestatic liver disease, short bowel and other fat malabsorption states, and in premature infants under specialist care. It is also taken widely as a skin and general-health supplement.

Cell membranes are built from fats that are easily damaged by oxidation, a chain reaction that spreads once it starts. Vitamin E sits inside the membrane and absorbs the damaging free radical, breaking the chain before it can travel further. That is why it is described as protecting cells from oxidative stress.

Usually none at ordinary doses. High doses can cause nausea, diarrhoea, stomach cramps, tiredness and headache.

High-dose vitamin E over long periods increases the risk of bleeding, particularly in anyone taking warfarin or another blood thinner, and it is usually stopped before surgery. More is not better: large doses have not been shown to prevent heart disease or cancer and have been linked to harm in some studies. Tell your doctor about a bleeding disorder, vitamin K deficiency, or if you are pregnant.