Mary Oates suffered from a host of seemingly unconnected and unpleasant health issues for a decade. 'I had such severe yeast infections I was taking Diflucan [anti-fungal medication] preventatively every month,' says 40-year-old Oates. 'I started to think there was something really wrong with me, maybe I had cancer? My gynaecologist was at a loss. To add to my fungal problems, I was running to the toilet every time I ate with chronic stomach pain and diarrhoea. I lost one of my toenails to a fungus.' A friend suggested she see Susan Jamieson from the Holistic Healthcare Practice in Central. 'So I went to her with what I thought were my three unrelated problems: fungus, yeast and digestion.' Jamieson organised a battery of tests, including blood work, urine and hair sample analysis. When the results came back they showed a heavy metal imbalance in Oates' body. She was depleted in iron, and also had surprisingly elevated copper levels. Jamieson explains that while we can cope with small amounts of some heavy metals, problems start when the body becomes overloaded. 'She prescribed a strong prescription iron pill, zinc supplements, plus a probiotic [supplement containing good bacteria],' says Oates. 'I also eliminated yeast from my diet, and I haven't had a problem in two years.' So what exactly are heavy metals, and how can they harm the human body? Dense chemical elements, such as iron, copper, selenium and zinc are essential to maintain the body's metabolism, but only in small amounts. The heavy metals we hear most negative stories about - mercury, lead, arsenic and cadmium - are not found naturally in the body and can definitely be poisonous even at low concentrations. Cadmium, for instance, can be found in cigarettes and some long-life batteries. Long-term exposure to cadmium can cause lung and kidney problems. Lead residues can be found in food, water, plumbing, soil, dust and paint flakes in old houses or contaminated land. High levels of exposure can cause problems with kidneys, joints and the reproductive system, and acute or chronic damage to the nervous system. Heavy metals first made headlines in 1932, when sewage containing mercury was released by a chemical works into Japan's Minimata Bay. Mercury accumulated in sea life, eventually leading to severe mercury poisoning in local residents two decades later. In total, 500 people died as a direct result. Today, most people come into contact with small amounts of heavy metals on a daily basis from pollution, old plumbing and paint, drinking water, cigarettes, soil pollution, dental amalgam fillings - and from seafood. Many people are anxious about the alleged high mercury content in fish from China. In reality, how big is the threat for Hongkongers? Family GP Michael Cheng says there are no studies showing heavy metals are an everyday danger. 'A lot of people are concerned about heavy metals. To justify this worry, you have to be able to prove it, and there are no definitive answers out there,' Cheng says. 'Of course, heavy metals are no good, but the question is, at what level are they no good? We know mercury is dangerous; we know lead poisoning is dangerous, but we are talking about huge doses. I won't stop eating seafood. These foods contain important nutrients, you must be careful not to throw the baby out with the bathwater.' Paediatrics Professor Fok Tai-fai at the Chinese University of Hong Kong is an expert in the field of heavy metals. Fok says the only heavy metal Hongkongers should be concerned about is mercury, and then only if you are a woman of childbearing age who consumes a lot of fish. 'We carried out a study and looked at the mercury content of available fish in the markets in Hong Kong, and all were within safety limits. Local fish is safe. But every fish contains mercury, so [as a pregnant woman] if you eat a lot - even if the mercury limit is at safe levels - you are consuming too much mercury. Big predator fish, tuna and shark for example, have a higher mercury content. 'Fish is a good source of protein which is easily absorbed, and mothers need protein during pregnancy, but they shouldn't eat too much.' Fok says that although in North America the mean monthly fish consumption of women of childbearing age is 56 grams, in Hong Kong it is a staggering 2.012kg. 'If a pregnant woman consumes a lot of mercury it can cross the placenta and damage the foetus, including causing cerebral palsy and visual and hearing impairment.' Fok says no one else is significantly at risk. Jamieson, however, maintains the problem is far more widespread and is finding it increasingly prevalent in her patients' problems. 'Acute toxicity - mercury poisoning from drinking water after the industrial pollution of rivers - we all know about. But it's the chronic toxicity that may go on for years that people don't talk about. Doctors don't study this as part of their normal medical training. 'The more you look, the more you find low-grade toxicity - mercury from fillings, lead from water pipes. Our body should be able to excrete this, but people vary in their ability to do this. If your intake exceeds your ability to excrete, then you have a problem.' Jamieson says she sees at least four patients a day for anxiety and depression symptoms, and around 70 per cent have metal toxicity problems, mostly mercury related. She also says studies have shown attention deficit hyperactivity disorder and autism in children have been correlated to elevated levels of mercury or lead, and there are a host of other problems that can be attributed to the effect of different heavy metals. Jamieson suggests taking antioxidants and vitamin C supplements every day to help the body excrete heavy metals more effectively. Regardless of the experts' differing opinions about the dangers of heavy metals, people are increasingly worried about living in a toxic environment and the effect it has on their general health. Thirty-eight-year-old Katie Smith first became interested in heavy metals after she had a miscarriage. 'I wanted to know why, so I went to see a nutritionist and she had my hair tested to see if my heavy metals were out of balance. I'd read that too much mercury could affect pregnancy. The test did show I was particularly high in mercury so I stopped eating fish altogether. She also gave me homeopathic powders to flush my system of toxins. Something worked because I fell and stayed pregnant.' Eight year-old Luke has sensory processing disorder and his mother Stacey worries it could be as a result of being exposed to lead as a baby in London. They lived in an old house which she now suspects had lead pipes. She is waiting for results of a hair sample analysis. 'It's a totally safe, easy and non-invasive way to get an indicator.' No one would disagree that it is non-invasive, but there is contention among experts as to how accurate hair sample analysis really is. 'If you send the same hair to five different labs in America, you will get five different results,' says Fok. 'The heavy metal content measure in the hair is very inaccurate. The results are distorted because of contamination, the environment, shampoo, and so on.' Jamieson is quick to point out the Environmental Protection Agency in the US considers it a viable method of screening, and she has and does use it successfully for diagnostic purposes in her clinic. The fact is that more people are making the choice to investigate further because, like Mary Oates, they hope it may just give them the answer to their problem.