Egg whites contain albumen, an important source of protein, and no fat, the researchers say.

Eggs are an excellent source of B vitamins, which are needed for vital functions in the body, and also provide good quantities of vitamin A, essential for normal growth and development, the researchers said.

An egg's vitamin E content protects against heart disease and some cancers; there's also vitamin D, which promotes mineral absorption and good bone health.

Eggs are rich in iodine, for making thyroid hormones, and phosphorus, essential for healthy bones and teeth.

Girls who eat an egg a day in their teens may give themselves additional protection against breast cancer in later life.

It is the essential nutrients in eggs, such as amino acids, vitamins and minerals that may be responsible for this protection.

Eggs are also low in calories - a large egg contains only 75 calories and 5 grams of fat - and other research suggests they can help you lose weight.

Health experts used to recommend a maximum egg consumption of three a week to avoid a rise in blood cholesterol levels. But since evidence has shown that it is saturated fat intake that affects cholesterol, advice has changed.

Now Britain's government's Foods Standards Agency (FSA) says there is no limit as long as they form part of a healthy, balanced diet.