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A study of nearly half a million people in China suggests a daily egg may reduce the risk of heart disease and strokes.

Experts stress any egg consumption needs to be part of a healthy lifestyle to be beneficial.

But fears that eating too many eggs can be bad for you appear to have been laid to rest.

"One can deliberate on the many limitations and caveats of nutritional research, but the take-home message of this research from a large study from China is that at the very least up to one egg a day is not linked with raised cardiovascular risk, and at best up to one egg a day may even have health benefits," says Prof Nita Forouhi, of the University of Cambridge, commenting on the work.

The study, in the journal Heart, follows years of bad press for the humble egg - from salmonella scares to cholesterol fears.

BBC News takes a crack at separating the issues.

How many?

These days most doctors encourage the eating of eggs as part of a healthy diet, as they are one of nature's most nutritionally dense foods - containing high levels of protein, Vitamins A, D, B and B12, as well as lutein and zeaxanthin that can help prevent eye damage in old age.

"One - even two - a day is absolutely fine," says Dr Frankie Phillips, of the British Dietetic Association.

"People shouldn't be frightened of eating too many eggs."

Perhaps the only caveat, says Dr Phillips, is that eating too much of any one particular food "means missing out on other nutrients in other foods".

Also, while eggs are "a great source of protein", Dr Phillips cautions that typically we already have plenty of protein in our diets and too much (two or three times the recommended daily amount) "can put a strain on kidneys".

The British Heart Foundation (BHF) dropped its advice to limit egg consumption to three a week in 2007 in light of new evidence about cholesterol.

Cholesterol

According to current NHS advice, "although eggs contain some cholesterol, the amount of saturated fat we eat has more of an effect on the amount of cholesterol in our blood than the cholesterol we get from eating eggs".

In other words, when it comes to cholesterol, eggs are not the problem - saturated fat is. So it's important how you cook them.

Image copyright PA Image caption The benefits of an egg have been embraced by many diets, including the high-protein Atkins diet

According to Heart UK, one average egg (58g; 2oz) contains about 4.6g of fat, about a teaspoon. But only a quarter of this is saturated, the type that increases cholesterol levels in the body.

Add butter or cream, and it's a different story.

Salmonella

Former Health Minister Edwina Currie will forever be associated with the health scare she prompted after comments about eggs and salmonella.

In December 1988, she said: "Most of the egg production in this country, sadly, is now affected with salmonella."

Mrs Currie's statement eventually led to her resignation.

However, there was a problem with salmonella in eggs at the time. And by the 1990s producers had started a vaccination programme.

Now, 30 years on, UK eggs are among the safest in the world - at least where salmonella is concerned.

The Lion Mark, found on most commercially available eggs, shows the egg has been laid by a hen vaccinated against salmonella.

And last year, eggs with the Lion Mark were declared safe even for vulnerable groups such as pregnant women and young children.

Experts said the risk of salmonella in a runny egg "is now so low you needn't worry".

Image copyright Getty Images Image caption How we eat our eggs plays a significant part in their health benefits

How to cook them?

In terms of how we cook an egg, they are arguably at their most simple and nutritious boiled or poached.

Most dietitians do not recommend frying an egg, because of the associated fat content and increased cholesterol intake.

Raw or lightly cooked eggs, as found in popular foodstuffs such as mayonnaise and ice cream, are fine provided they have the Lion Mark and are hens' eggs (not duck or quail) sourced in the UK.

Cooking eggs thoroughly is the safest option if you are still concerned about food poisoning.

How to store them?

Never buy eggs that are broken or cracked, in case they have been infected by dirt or bacteria.

BBC Good Food recommends storing eggs in the fridge, in their box or a separate covered compartment.

Whites last for up to three weeks in a container. Yolks will last up to three days. Both should be covered in cling film. Both can also be frozen for up to three months.

Many will know the trick of putting an egg in a bowl of cold water to check it is still fresh. If the egg sinks to the bottom of the bowl, it is fresh. If it sits on the surface, it is less so.

Image copyright Reuters

Best-before dates should be heeded. Most eggs have a shelf-life of 28 days from the date they were laid.

And basic kitchen hygiene should be followed.

Egg allergy

Some people are allergic to eggs. It is quite common in children under five but rare for it to develop in adulthood.

Most reactions are mild:

redness and swelling around the mouth

stomach ache

vomiting

diarrhoea

Rarely, there is a severe, life-threatening reaction. Always seek medical advice.

For anybody not allergic, "all advice and evidence is they are good to eat in all their forms... but how you cook them needs to be looked at", says Dr Phillips.

And hold the salt.