AS the single most important element of earthly existence, oxygen has its life-and-death devotees in every one of us. However, while we're all the unwitting beneficiaries of dear old oxygen's essential presence in the air we breathe and the water we drink, a new cast of fans has recently become actively attracted to the taste-free, odourless gas which bears the chemical symbol O.

It's the A-list who've become O-lovers, and they're keen to put oxygen's vital properties to fresh use. Injured Manchester United and England soccer superstar David Beckham is just the latest in a long line of high-profile fans of oxygen, thus joining Hollywood health faddists like Uma Thurman, Kim Basinger, Sharon Stone, Woody Harrelson, Alec and William Baldwin, plus both Arquette sisters, Rosanna and Patricia.

Beckham's recent recourse to purer oxygen has a strictly medical purpose, however, unlike his silver-screen equivalents in body-conscious, new-age California. So, while Becks is apparently using a hyperbaric chamber in a bid to speed the recovery of his broken foot, Hollywood stars are simply investing in LA bars on Sunset Boulevard which dispense over-the-counter blasts of purified air to paying punters.

On this side of the Atlantic, Oxygen is a bar near Leicester Square in London which also offers both optics and oxygen canisters. In contrast, Bar Oxygen in Edinburgh stopped dispensing O two years ago, KO'd by the local fire department.

Meanwhile, in Glasgow, there's now no charge for the air in Air Organic: the bar-restaurant's owners felt that their special system for dispensing extra oxygen wasn't giving its clientele value for money. Elsewhere in the city, though, at the New Athena Health and Beauty Salon, you can have an hour in their hyperbaric chamber for (pounds) 35.

Oxygen's sudden emergence as a fashionable and profits-producing cosmetic accessory, as well as a staple of sports-page headlines, hasn't pleased those who have long used it medically. David Hinds is one man who can't disguise his chagrin at oxygen's new association with gloss and floss.

Hinds is the operator of the two hyperbaric chambers which, since 1994, have daily been assisting MS sufferers at the Multiple Sclerosis Therapy Centre in Maryhill, Glasgow.

''Our chambers aren't available to folk walking in off the street,'' Hinds stresses. ''They're comparable to the decompression chambers used for divers suffering from the bends, although we use less pressure in our hyperbaric process.

''We might occasionally take a non-MS referral from a consultant, but no-one ever receives treatment without their GP's knowledge. Everyone's MS is different to everyone else's, with

different symptoms and different reactions to our therapy.

''Nevertheless, on a weekly basis, we currently have 70 to 80 MS sufferers who feel some benefit from the hyperbaric chambers. Not everyone does, but there can be a help with bladder function or a reduction in fatigue.''

Folk suffering from exercise injuries - ie, sportsmen - are another group who can benefit from hyperbaric chambers. Why does oxygen help those, like Becks, suffering with mangled metatarsals? Simply put by one sports injuries specialist: ''Oxygen is the basic principle of every cell in our bodies. If any tissue requires regeneration, additional oxygen will help accelerate the healing process. In addition, there have been American scientific studies of college athletes using hyperbaric chambers, suggesting an increase in muscular efficiency and performance for those who do.''

Seeking to pluck cash out of the air, big business has naturally jumped on the oxygen bandwagon, offering a range of allegedly oxygen-suffused beauty products. Cosmetics companies Lancaster and Karin Herzog offer skincare creams and lotions filled with the stuff, claiming they're able to remedy ageing by boosting oxygen-starved skin cells.

Such bold claims induce an audible gasp from Professor Susan Ward, director of the Centre for Exercise Science and Medicine at Glasgow University. She's sceptical about oxygen being cited as a miracle rub-on cure, or as every city-centre pub's universal panacea.

''Oxygen doesn't dissolve well in water or into the body, so the problem with a lot of oxygen-laden products is that it escapes as soon as you take the cap off,'' Professor Ward says.

Skincare experts likewise take the view that the best way to deliver oxygen to the skin isn't via the daub-it-on-and-hope-it-soaks-through-the-skin route. They moreover feel sure that delivering oxygen to, say, acne would do nothing more than encourage acne bacteria to flourish.

Oxygen on tap in bars? Professor Ward continues: ''Oxygen levels drop in a crowded room or a confined space with poor ventilation. Equally, there is less oxygen at high altitude - but since Glasgow, for example, is effectively at sea-level we have all the oxygen we need.

''A normal lungful of fresh air contains 80% oxygen and 20% nitrogen, but the volume of oxygen in our body depends how efficient our lungs are in extracting oxygen from the air and transferring it into the bloodstream.''

At best, she feels, ingesting extra oxygen might result in the well-kent placebo effect, or lead to a fleeting cerebral high. Lung efficiency is

truly what counts in any case, and

Professor Ward goes on to add that this is inhibited by ageing: ''An 80-year-old doesn't exchange as much oxygen as someone younger.''

A spokesman for the New Athena Health and Beauty Salon in Glasgow carefully avoids all claims to medical efficacy with its hyperbaric chamber. ''It's a tool for relaxation and de-stressing,'' he says. ''The sensation is like being aboard a pressurised plane - your ears pop.

''Like every other commercial concern offering extra oxygen, what we're actually offering is cleaner air that's been filtered - pure oxygen is highly flammable, of course.''

Oddly, it would seem that the worse you feel before you enter the hyperbaric chamber, the better you'll feel stepping out of it after 60 minutes. What's the one thing that's best for a hangover? Drinking heavily the night before, of course - although a hyperbaric session the morning after is good, too.

Even this benefit, however, won't extend the life of the oxygen dispenser at Air Organic in Glasgow, as its spokesperson confirmed.

''It's still sitting in the bar, but it's not in use as its operation was proving too costly, both for us and for our customers. Most folk reckoned it cleared their head and made them feel relaxed. There was a benefit if you were feeling a bit ropey from the night before, but we're now open to offers for it.

''It cost us around (pounds) 2000, but with the agreement of the company who actually supervise it being turned on, we're now thinking of donating it to an old folk's home, or wherever it might do the most good.''

Perhaps some Tartan Army sub-branch of the David Beckham Fan Club might like to step forward and claim it - not for their own hangovers, but to send it down to Old Trafford. After all, every little bit helps in the pan-British battle to get England's hero ready for the World Cup.

Aye, right, they will. Don't hold your breath.

IT'S ALL IN THE BLOOD

A hyperbaric chamber contains air at an increased pressure. Increasing air pressure increases the concentration of oxygen in the air. Increasing the intake of oxygen loads the red blood cells, thus promoting healing.

Increased levels of oxygen can alleviate some symptoms of MS for sufferers.

Pub-goers offered the chance to inhale oxygen should note that it can lead to throat problems, if the oxygen is in dry and unhumidified form.