Eating purple coloured fruit can ward off age-related diseases such as Alzheimer’s, heart problems and cancer, scientists believe. The odds of developing multiple sclerosis and Parkinson’s disease may also be reduced by consuming blueberries, blackberries, blackcurrants or plums, according to a study by the University of Manchester. Researchers say one or two of the recommended five daily portions of fruit and vegetable should be purple fruit.

It is thought that a compound in purple fruit helps fight the harmful effects of iron, which can damage cells if it makes its way through the digestive system in the wrong form. Although we are often told of the healthy effects of the mineral, benefits are only felt if it reacts with other compounds in the body. Iron that does not react can prove poisonous to tissue.Compounds called polyphenols that make blueberries and other fruits purple are able to grab iron and keep it out of harm’s way. Green tea contains a similar compound, as does curcumin, the key ingredient of the curry spice turmeric.

Even chocolate may help but unfortunately red wine, does not have the healthy effects, the journal Archives of Toxicology reports. Lead researcher Professor Douglas Kell said: ‘We normally think of iron as something that is good for us.  And, in the right form, it is. But in the wrong form it is not good for you because what it does is react with things that are always knocking around in the body to make something very nasty indeed.’

Too much free iron could also stop vitamin C from helping the body fend off infections. Parkinson’s UK welcomed the research, saying that it reinforced the message that a healthy diet is essential to stay healthy. But the charity and the Alzheimer’s Research Trust said that more research was needed.