Although it's been around for some time, modern medicine is still baffled by the condition. The symptoms-including tremors, muscle rigidity and slowed movements-can so closely resemble a number of other disorders that PD is, in fact, notoriously difficult to diagnose.
Indeed, a recent study has reported that at least one in 20 Parkinson's cases is a misdiagnosis (Mov Disord, 2009; 24: 2379-85). This means that over 6000 people in the UK could be taking dangerous anti-Parkinson's drugs unnecessarily. Alarmingly, many of these drugs can even cause the symptoms they're meant to treat-such as confusion and involuntary movements-and such side-effects are not always reversible (Am Fam Physician, 2007; 75: 1045-8).
Medicine is also confused as to what exactly causes PD. The symptoms are thought to arise from a lack of the chemical messenger dopamine in the brain, which happens when the specific brain cells that produce it die or become impaired. However, researchers still don't know what triggers such a chain of events in the first place.
Also, recent evidence suggests that ageing is less important than has been previously believed (Environ Health Perspect, 2005; 113: 1234-8). Indeed, what's emerging is that environ-mental factors throughout life-such as what we eat, where we live and what we do for a living-are crucial pieces of the puzzle.
So far, it appears that exposures to particular toxins or foods can increase the risk of PD.
o Pesticides. Numerous animal and human studies link pesticides to PD. People living within 500 metres of land sprayed with pesticides have a 75-per-cent increased chance of developing the disease. In addition, those exposed to agricultural pesti-cides as a child or young adult have an even greater risk (Am J Epidemiol, 2009; 169: 919-26).
Household pesticide use is also associated with PD. US researchers reported that using insecticides and herbicides in your home or garden can double your risk of developing the disease (Lancet, 2000; 335: 1701; http://news.bbc.co.uk/2/hi/ health/738020.stm).
o Polychlorinated biphenyls (PCBs). These man-made organic com-pounds, formerly widely used in electrical and hydraulic equipment, were linked to PD in two US occupational studies, which found that female workers exposed to PCBs were around two to three times more likely to die with PD compared with the general population (Environ Health, 2006; 5: 13; Epidemiology, 2006; 17: 8-13). There's also considerable animal and laboratory evidence to back this up. In fact, even low levels of PCB exposure-as seen in the general population-may have the poten-tial to disrupt normal dopamine functioning in the brain, which could eventually lead to PD (Toxicol Sci, 2006; 92: 490-9).
o Heavy metals. One study found that those with the highest lifetime lead exposures are twice as likely
to have PD as those with the lowest exposures (Environ Health Perspect, 2006; 114: 1872-6). Other metals, including aluminium, mercury, copper, manganese and iron, may also be risk factors (Neuroepidemiol-ogy, 1999; 18: 303-8).
o Dairy. Harvard researchers found that high intakes of dairy foods nearly doubled the risk of PD in men (Ann Neurol, 2002; 52: 793-801), and there's a slightly increased risk in women, too (Am J Epidemiol, 2007; 165: 998-1006).
o Fruit. Researchers at the University of Hawaii found a connection between high intakes of fruit and fruit juice, and PD in middle-aged men. Those who ate more than three servings a day had a 70-per-cent higher risk, while those eating only one or more servings a day increased their risk by 55 per cent. The researchers noted that it is unlikely that fruit itself is the problem but, rather, the increased exposure to plant-borne toxins, pesticides or herbicides (Presentation at the American Academy of Neurology Annual Meeting in Honolulu, 2003).
These data suggest that lifestyle changes, such as choosing organic fruit, limiting dairy, and avoiding pesticides and other toxic chemicals, may help to prevent PD. Also, drinking tea (CNS Neurosci Ther, 2008; 14: 352-65), taking regular exercise (Mov Disord, 2008; 23: 69-74) and maintaining a healthy weight (Neurology, 2006; 67: 1955-9) all appear to reduce PD risk.
Interestingly, experts now reckon that genes alone are responsible for less than 10 per cent of PD cases-and even then, the environment may play a part (Environ Health Perspect, 2009; 117: 117-21). It's likely that environmental factors, such as diet and pesticide exposure, interact with genes to bring about the disease, suggesting that, with more research, the vast majority of cases may be preventable.
WDDTY VOL 20 NO 11