Of all substances purported to be responsible for triggering health scares, mercury does seem to possess an uncanny knack of cropping up more frequently than most. This week it has once again regained the media spotlight because of its supposed damaging presence in amalgam fillings. Mary Stephenson, a 59-year-old from Hampshire, claims that she was lifted from a 40-year black hole of depression when 19 silver fillings were removed from her mouth. Since a dentist replaced them with white plastic, Stephenson says she is "a new person", convinced that mercury poisoning was to blame for her illness. Whether or not her diagnosis is accurate, its premise is nothing new.
Debate has raged since the 1970s about the potential risks of amalgam fillings which contain 52% mercury and 48% copper, zinc and silver. Although used by dentists for 150 years, mercury's safety had been in doubt ever since its use in the preparation of felt hats was blamed for causing St Vitus's Dance among hatmakers. Today, a growing band of medical professionals link amalgam fillings to conditions ranging from gum disease, migraine and depression to Alzheimer's, kidney disease and multiple sclerosis. Dr Jack Levenson, founder of the British Society for Mercury-Free Dentistry and co-author of The Menace in Your Mouth, goes as far as stating that mercury poisoning is an epidemic in the UK. Having removed the fillings of more than 6,000 patients over the past 20 years, he claims that nearly all those he has treated have reported a general improvement in their health.
"The British Dental Association's (BDA) figures say 3% of the population are particularly sensitive to mercury, but when you have an outbreak of flu, 0.4% counts as an epidemic," Levenson says. "I believe that many conditions fashionably attributed to viruses could in fact be caused by mercury toxicity." He is not alone. Harley Street dentist and president of the International Academy of Oral Medicine and Toxicology, Dr Anthony Newbury, was among the first UK-based dentists to introduce the idea of a mercury-free practice in 1979. He did so after attending a lecture in the USA where mercury leakage from fillings was linked, controversially, to chronic muscle and joint problems and excessive fatigue. Says Newbury: "Everybody knows mercury is toxic, and if they brought it out now for use in fillings they'd be laughed out of the country."
Such vociferous campaigning cannot be taken lightly. Mercury is, after all, known to be the second most toxic metal on the planet after plutonium. Most dentists, including those who are against an amalgam filling ban, now agree that the substance does not, as previously believed, become "safely sealed" when mixed with other metals and that it does have the potential to release toxic vapours in the mouth, particularly during chewing. Mercury fillings are already banned in Sweden, so why not here? It is a question curtly dismissed in an official statement distributed by the BDA whenever another mercury scare arises. "Each year around nine million fillings are carried out in England and Wales alone, yet sensitivity to amalgam is incredibly rare," it reads. "The BDA takes its guidance on the use of amalgam from the Department of Health's Committee on Toxicology, which has found no reason why its use should be withdrawn."
In the UK, the majority of dentists continue to use amalgam fillings because, says Jo Tanner, a BDA spokesperson, "they are hard-wearing, long-lasting and relatively cheap compared with plastic ones." Although it is acknowledged that toxic vapours can be released from mercury-containing fillings, pro-amalgam experts argue that they are present in minute amounts and affect those only with an extreme hypersensitivity to mercury. Indeed, removing the fillings can cause more vapours to be released than leaving them in place. Plenty of research proves they are safe to use, even in children. In a study published in the journal Pediatric Dentistry, researchers at the University of North Carolina found children were unaffected by amalgam fillings and concluded that "very little mercury is ever going to be absorbed by the body".
Were it not for the emergence of potential mercury risks unrelated to dentistry, it might indeed be written off as scare-mongering. Yet unwelcome warnings about mercury poisoning persistently seep in from other avenues of the medical and scientific professions. In August 2004, a decision was made to take mercury, a known neurotoxin, out of vaccines given to very young British babies following its links with autism. Doctors were told via a letter, that despite the Department of Health's instance that thiomersal, the form of mercury used in medication, was perfectly safe, it was to be phased out of infant vaccinations and replaced by a new 5-in-1 jab. It was a move welcomed by Professor John Oxford, professor of virology at St Bartholemew's Hospital in London, who said that "any doubt whatsoever" over the safety of mercury should lead to it being removed.
Exposure to mercury in the environment - through food and household products - is also consistently highlighted as harmful by some experts. Of particular concern is the consumption of seafood and oily fish, both high in mercury, by vulnerable groups such as women of childbearing age and young children. In the environment, mercury is released naturally into the ocean through the earth's crust but it is also absorbed into the sea by industrial pollution. Once present in water it is converted into methyl mercury, a more toxic form of the substance when eaten by human beings. "Predatory fish at the top of the food chain tend to contain much higher levels of mercury than others - it is stored in the fatty tissue of fish and passed up the food chain," says Dr Hannah Theobald, a nutrition scientist at the British Nutrition Foundation. "For that reason, pregnant and breast-feeding women and anyone under 16 are now advised not to eat swordfish, sharkfish and marlin and should consume only one piece of oily fish, such as mackerel, each week."
But researchers continue to unearth other findings that fuel the mercury debate. Following a study in America, the government last year introduced precautionary guidelines about the amount of tuna fish consumed by young women. Anyone of childbearing age should eat no more than two medium-sized cans of tuna or one fresh tuna steak each week - the equivalent of six rounds of tuna sandwiches - in order to protect the nervous system of an unborn foetus, say government advisers. Mercury levels in the foetal brain are up to seven times higher than in maternal blood. "It is thought that a woman's blood mercury levels during pregnancy depend partly on how much she has been exposed to methyl mercury in the months beforehand," Theobald says. "It is only advice and people must not assume that the health benefits of oily fish, which are immense, don't still hold true for most of us."
Professor Tom Sanders, of the nutrition department at King's College London insists the risks of mercury poisoning in the diet remain low and that even those who eat fish more than once a week are unlikely to be affected. It is true that, as Sanders claims, evidence against mercury is inconclusive. Many, though, remain adamant that the removal of mercury in any form has transformed their lives for the better. Ruth Moult, 31, from Somerset, has multiple sclerosis but found many of her symptoms improved when three leaking mercury fillings were removed. "The effects on my MS have been a great improvement in energy levels, regular sleep patterns, a general sense of well being that I didn't have before, and I no longer have that 'heavy legs' feeling," she says. "Now, I always insist to friends and family not to have mercury fillings put in their mouths. Standard NHS dentists can appear exasperated when you ask for a white, but don't let this put you off."
