It was once thought to inhabit primarily the large intestine, but now it's understood to live primarily in the small intestine, according to Dr Gaier. When candida is permitted to proliferate, it can perform an astonishing metamorphosis, changing from a simple yeast cell into a much more harmful "mycelial" fungal form. Under the microscope, the cell appears to sprout roots and branches; these burrow their way into the walls of the intestine, and ultimately can spread throughout the body, with potentially widespread adverse effects (Current Biology, 1997; 7: 691-94).
In fact, we all have antibodies to candida in our blood, which suggests that symptomless, low level systemic invasions may be commonplace. However, when the immune system is under pressure, say, as a result of stress, illness or medication, the infection can take hold, causing a wide variety of symptoms apparently unrelated to the gut (see box, p 1). In particular, if the candida infection reaches the brain, it will cause a host of cerebral and mental symptoms, which again tends to reinforce the conventional dismissive diagnosis that the patient's problems are psychogenic in origin.
Dr Leo Galland, the noted US nutritional doctor, says there is new evidence suggesting that the antibodies directed against candida may cross react with organ tissues, particularly in the thymus gland and ovaries, producing a kind of auto immune reaction. This can lead, he says, to ovarian failure, premature menopause and infertility. Antithymus antibodies may interfere with immune function and lead to a vicious cycle: yeast infection leads to immune suppression, which leads to worse yeast infection (Lancet, 1991; 338: 1238-40; NE J Med, 1989; 320: 245-6).
Perhaps the most insidious damage, however, is to the lining of the gut. Besides penetrating the gut wall in its mycelial fungal form, candida overgrowth is often associated with an increase of toxins called polyamines, which attack the mucosal cells of the gut wall. This results in excessive intestinal permeability popularly known as "leaky gut". Because the gut wall leaks, it can no longer function as an effective barrier. Thus, all manner of substances, some toxic, can pass through in particular undigested food molecules (See WDDTY vol 8 no 5). Such foreign bodies, circulating in the blood, will sensitise the immune system and often cause adverse reactions to food, showing up as either as allergy or intolerance. These, in turn, can result in a bewildering array of symptoms, many of which overlap with those from C albicans. Diagnostically separating food sensitivity from candidiasis is therefore complex. Two recent laboratory tests, however, have made the clinician's life easier the ethanol test and the hydrogen breath test (available from Biolab in London: 0171 636 5959).
C albicans has also been found to be a major allergen in its own right, which can produce a hay fever type of reaction, resulting in hives, asthma and irritable bowel syndrome. Many women with chronic vaginitis have an allergic vaginitis provoked by candida (L Galland in R Jenkins et al, Post Viral Fatigue Syndrome, John Wiley & Sons, 1991).
The evidence is also building that C albicans either contains or produces toxic substances, which can interfere both with the immune system and brain function. Many of these toxins are alcohols which are produced by the reaction of sugars in the food and yeasts in the gut. One of the main "sugar alcohols" is arabinitol, which recent studies have shown to be a powerful neurotoxin. In America, two laboratories now offer tests for the presence of these alcohols in the blood. Dr Galland finds them particularly useful for patients complaining of neuropsychiatric disorders or autism.