Gluten is found in wheat, rye and barley and gives food a chewy texture and elasticity during the baking process.

Only around 1 per cent of people are genuinely gluten-intolerant, a condition called coeliac disease, however some estimates put the proportion of adults adhering to gluten-free diets in the UK at more than 12 per cent.

The researchers behind the study have suggested that people who are limiting their gluten intake who are not coeliacs should think again, and pointed out that there is no evidence that going gluten-free has any health benefits.

The Harvard team examined 30 years of medical data from nearly 200,000 patients.

They found that most participants had a gluten intake of below 12g a day, which is roughly the equivalent to two or three slices of wholemeal bread.