Image copyright Getty Images Image caption The effects of caffeine can vary from person to person

Moderate coffee drinking is safe, and three to four cups a day may have some health benefits, according to a large review of studies, in the BMJ.

It found a lower risk of liver disease and some cancers in coffee drinkers, and a lower risk of dying from stroke - but researchers could not prove coffee was the cause.

Too much coffee during pregnancy could be harmful, the review confirmed.

Experts said people should not start drinking coffee for health reasons.

The University of Southampton researchers collected data on the impact of coffee on all aspects of the human body, taking into account more than 200 studies - most of which were observational.

Compared with non-coffee drinkers, those who drank about three cups of coffee a day appeared to reduce their risk of getting heart problems or dying from them.

The strongest benefits of coffee consumption were seen in reduced risks of liver disease, including cancer.

But Prof Paul Roderick, co-author of the study, from the faculty of medicine at University of Southampton, said the review could not say if coffee intake had made the difference.

"Factors such as age, whether people smoked or not and how much exercise they took could all have had an effect," he said.

Image copyright Getty Images Image caption Everything in moderation, including coffee

The findings back up other recent reviews and studies of coffee drinking so, overall, his message on coffee was reassuring.

"There is a balance of risks in life, and the benefits of moderate consumption of coffee seem to outweigh the risks," he said.

The NHS recommends pregnant women have no more than 200mg of caffeine a day - two mugs of instant coffee - because too much can increase the risk of miscarriage.

This review suggests women at risk of fractures should also cut back on coffee.

For other adults, moderate caffeine intake equates to 400mg or less per day - or three to four cups of coffee - but that isn't the only drink (or food) to bear in mind.

How much caffeine in my drink?

one mug of filter coffee: 140mg

one mug of instant coffee: 100mg

one mug of tea: 75mg

one can of cola: 40mg

one 250ml can of energy drink: up to 80mg

bar of plain chocolate: less than 25mg

bar of milk chocolate: less than 10mg

The researchers say coffee drinkers should stick to "healthy coffees" - which avoid extra sugar, milk or cream, or a fatty snack on the side.

And they are calling for rigorous clinical trials on coffee intake to find out more about the potential benefits to health.

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At present, the researchers said pinning down exactly how coffee might have a positive impact on health was "difficult" but it could be down to the effects of anti-oxidants and anti-fibrotics, which prevent or slow damage to cells in the body.

Commenting on the BMJ review, Eliseo Guallar, from the John Hopkins Bloomberg School of Public Health, said there was still uncertainty about the effects of higher levels of coffee intake.

But he added: "Moderate coffee consumption seems remarkably safe, and it can be incorporated as part of a healthy diet by most of the adult population."

Image copyright Getty Images Image caption Best not to opt for sticky, sweet snacks with your espresso

Tom Sanders, professor emeritus of nutrition and dietetics at King's College London, said coffee drinkers may be healthier people to start with - and that could skew the findings.

"Coffee is known to cause headaches in some people and it also increases the urge to go to the toilet - some people chose not to drink coffee for these reasons.

"Patients with abnormal heart rhythms are often advised to drink de-caffeinated coffee. Caffeine also acutely increases blood pressure, albeit transiently. "