half of takeaway pizzas have the maximum daily recommended level of 6g of salt, a new survey has found.
Takeaway pizza has up to two and a half times more salt than supermarket varieties, according to a survey of 199 margherita and pepperoni pizzas.
One restaurant's pizza had 10.57g of salt, making it saltier than seawater.
But supermarket pizzas were still classified as unhealthy. None was found to be low in salt, fat or saturated fat.
Half of all takeaway pizzas surveyed contained the entire maximum daily recommendation of salt which is 6g.
Manufactured trans-fat, which presents a serious health risk and can cause heart attacks and strokes, was found in 84pc of the takeaway pizzas.
The target for salt content in pizza set by health experts is a maximum of 1.25g of salt per 100g. Only 16pc of the takeaway pizzas tested met this target compared to three quarters of the supermarket pizzas.
A Pizza Express margherita pizza from a supermarket contained almost half the amount of salt than the restaurant equivalent.
Survey organiser Professor Graham MacGregor said: "Atlantic seawater contains 2.5g of salt per 100g.
"This allows a comparison to be made between the amount of salt in food and seawater. It also allows consumers to realise the huge and unnecessary amount of salt added to food by the food industry."
Health expert Victoria Taylor added: "Nobody would choose to eat an entire teaspoon of salt in one go, yet by eating some of these pizzas, that's what we're doing.
"We need clear traffic light labelling to help us all understand what's really in the food we are buying."