Health: Take two leeches before meals

Iron is essential for good health, but you can have too much - which is why blood-letting still has a role in medicine.

Fussy children are still told to "eat your greens" by concerned parents. One spinach-canning company even invented a pipe-smoking character with improbable forearms and a cruel facial disfigurement in an attempt to improve the image of green, leafy vegetables.

The wonder ingredient in spinach is iron, which is, indeed, necessary for good health. With no iron in your diet, you won't last very long. But, like everything else, excess can be harmful. A team in Finland, whose research was reported last week in New Scientist has even suggested that too much iron may increase the risk of a heart attack.

The place in the body you will find most iron is the blood. Blood contains red cells; red cells contain haemoglobin; and each haemoglobin molecule contains four atoms of iron. The function of haemoglobin is to transport oxygen from the lungs to the tissues, and a healthy adult carries about 150 grams of haemoglobin in every litre of blood. Anaemia can occur if the level falls below about 90, although some patients have survived with levels as low as 15 or 20. Such cases are not that uncommon, occurring in Jehovah's Witnesses who bleed from emergency surgery and refuse blood transfusion. So there is a wide margin within which the haemoglobin level can drop before it becomes fatal (although anyone with significant anaemia is likely to get tired and short of breath easily). This is why humans can donate a pint of blood without ill effects and, it seems now, with possible benefits. The Finnish team looked at those who donated blood regularly and those who did not. Of their donors 0.77 per cent had heart attacks, while a staggering 12 per cent of non-donors were apparently at risk.

The postulated, rather complex, mechanism for this apparent protective effect is that high iron levels lead to the formation of a particularly damaging form of cholesterol, well known for causing heart disease. Cynics have already suggested a more simple and prosaic explanation: that blood donors are more likely to be conscious of their health in general, to be non-smokers, to take regular exercise and so to be at lower risk of heart disease. As usual with scientific medical papers these days, all that the research really throws up is that a far bigger and better designed trial is needed.

The idea that blood-letting may have health benefits smacks of witchcraft or, at least, of very old-fashioned medicine. But that is far from the truth. For example, the condition of polycythaemia is often fatal if left unchecked. It is essentially the over-production of red blood cells (akin to the effect leukaemia has on white ones) and can give victims a haemoglobin level of 200 or more. The over-concentrated blood takes on the viscosity of treacle, and cells begin to clog up delicate organs such as the eye. The immediate solution, even these days, is to bleed the patient by up to a litre at a time. The liquid components of blood are renewed within hours, rather than the weeks it takes to make new cells, so in a very short time the patient's blood is thinner and flows more freely. Other rare conditions that either result in or are caused by iron overload, such as thalassaemia and some forms of porphyria, are also treated by blood- letting. Unfortunately blood from these patients is not thought suitable for transfusion.

These days we bleed patients scientifically. We use sterile needles, local anaesthetic and pre-prepared plastic bags. In times gone by, physicians used leeches. Thankfully, those days are long gone. Physicians would never now dream of applying a leech. Plastic surgeons, however, would and sometimes do. When a small part of the body, such as a finger, is sewn back on after accidental amputation, it is the thin, fine veins, rather than the robust arteries, that are most difficult to identify and reconnect. Blood flows into the finger, but cannot escape. The injured part becomes engorged with blood and is at risk of gangrene. Enter the leech. It can remove just the right amount of blood from the fingertip to keep things moving nicely, producing its own local anaesthetic and anticoagulant.

Spinach, though, has an altogether more modern counterpart. Erythropoeitin, or "epo", is a naturally occurring hormone that stimulates production of red cells in the bone marrow. The basic aim is the same - to boost the oxygen-carrying capacity of the blood; this, along with the fact that it is undetectable in drug screens, is why epo is used surreptitiously by some athletes. It is used by doctors to treat some forms of anaemia caused by chronic disease, but athletes who use the drug to raise their haemoglobin levels run the same risks as someone with untreated polycythaemia - stroke, blindness and kidney failure.

Unfortunately, if the Finnish researchers have indeed made a breakthrough, it may have come just at the wrong time. Within the next 10 years, doctors expect to be using synthetic rather than donated blood. Donor product has a lot of problems. For a start, every bag these days carries a label stating that it is not guaranteed free from infection. Great lengths are taken to ensure that it is free from known viruses such as Hepatitis C and HIV; the big worry is viruses that have not yet been identified. Earlier this year, the Department of Health announced the start of a program of "leukodepletion", to reduce the number of white cells present in a bag of blood for transfusion - white cells are thought most likely to transmit new-variant CJD, better known as the "human form of Mad Cow Disease". Then there are the problems of "massive transfusion", usually defined as replacement of more than half the recipient's normal blood volume. Blood in a bag does not clot. It's not supposed to, of course, but it won't clot inside the recipient either. It has added preservative chemicals and is usually very cold. "Massive transfusion" is a complete disease in itself.

The limited findings from this study may well be pounced upon by the Blood Transfusion Service, always desperate for new recruits. All you used to get was gratitude and a cup of tea. A 20-fold drop in the risk of heart disease would be a much stronger incentive. But even if iron is eventually shown to play a part, its role will probably be a very small one when measured against other risk factors. So the advice is still the same - stop smoking, have a low-fat diet, exercise and carry on eating your greens. At least for now.