Ironically, many people may have a chronic low intake of iron as a result of trying to eat more healthily.

Alternatively, the researchers said the protective effect could be because some patients with low intake were actually in the terminal phase of their lives.

Those eating the most, 1¼ extra teaspoons or more, were 72 per cent more likely to get it than those on low intake.

Low intake of vegetables accounted for 7.6 per cent and low in-take of fruits 7.5 per cent.

It failed to adjust for the overall balance of a diet, for instance, meaning those with high protein diets might also have low intakes of fruit and vegetables.