Every day, millions of people in the Middle East and growing numbers in the West smoke water pipes - most believing it is far safer than smoking cigarettes. But new Israeli research indicates that it is even more harmful.

Lea Bentur, head of the Paediatric Pulmonary Unit at the Rambam Health Care Campus in Haifa, decided to probe the acute effects of smoking them - widely known as hookah or nargilah - after becoming aware of how accepted it is among Israeli youngsters and how little research has been conducted.

She said: "Whenever I see a teenage patient who has asthma I ask them if they smoke. Usually, when they say 'no I don't', I say 'nargilah?' and they say 'nargilah yes, but never cigarettes.'"

In recent years, nargilah smoking has become widespread in the West and the equipment and consumables are sold on many British high streets. It is especially popular among Jewish youngsters who have tried it in Israel during study stints or gap years.

Dr Bentur recruited 45 people and gave each a nargilah with a single dose of flavoured tobacco, which they smoked for up to 30 minutes. Afterwards, she tested their carboxyhaemoglobin, meaning the level of the poison carbon monoxide bound to their haemoglobin - and found it to be within a "high toxic range".

Carboxyhaemoglobin, which can hinder delivery of oxygen to the body, is normally less than two per cent of a person's haemoglobin, and in a cigarette smoker would be expected to be three per cent to four per cent. In the nargilah test it increased to higher levels - reaching more than 20 per cent in three subjects including 26 per cent in one.

"If someone would come to the emergency room with 26 per cent I would admit him, give him oxygen, and consider treatment by hyperbaric chamber," said Dr Bentur.

She also observed significant increases in blood pressure, heart and respiratory rates.

The sweet, flavoured tobacco used in nargilahs is often presumed free from nicotine and other harmful substances, but Dr Bentur said that it contains a similar number of harmful components to conventional tobacco including nicotine.

It is a misconception, she added, that the water in the pipe filters harmful elements from the smoke - it makes the smoke more moist, and therefore, more pleasant.

The study will be published in Chest, the journal of the American College of Chest Physicians. It concludes that the immediate effect on the body indicates that nargilah is dangerous and that research should be undertaken into the long-term effects.

With the sale of nargilah tobacco less regulated than cigarettes in many countries, it also supports "interventions to control the continuing global spread of water pipe smoking, especially among youth".

While many British youngsters used to get their first taste of nargilah during post-GCSE Israel tours, youth-movements have now made these tours entirely non-smoking - despite the fact that in Israel nargilah is legal for under-18s - while permitting it during gap-year programmes.

Francesca Wolfe, national director of FZY, said that nargilah-smoking encourages "anti-social" behaviour, excluding from social groups youngsters who do not want to take part.