Regularly downing three units of alcohol a day can double the likelihood of developing involuntary (essential) tremor, suggests research published ahead of print in the Journal of Neurology Neurosurgery and Psychiatry.

Essential tremor is a common neurological disorder, with an estimated 650,000 people in the UK and five million in the US over the age of 60 affected.

The exact cause is unknown, but it is thought to be the result of damage to particular brain (Purkinje) cells and disrupted signalling between the nerve "junction boxes" or synapses.

The research team base their findings on an assessment of lifetime alcohol consumption and neurological symptoms in almost 3,300 people aged 65 and above.

All participants were part of a large population survey of major age related conditions in three areas of central Spain (Neurological Disorders in Central Spain study, or NEDICES). Just over half (56%) regularly drank alcohol.

They were first assessed between 1994 and 1995 and then again three years later between1997 and 1998, when essential tremor was diagnosed in 76 of them.

Compared with those who had not developed tremor, those who did were significantly more likely to have been drinking regularly and for longer.

After taking account of factors likely to influence the results, such as lifetime cigarette smoking and depression, those who drank at least three units a day more than doubled their risk of essential tremor.

Every additional year of regular daily drinking at this level upped the risk by 23%. Even those who drank fewer units, but who drank regularly, increased their risk, although not to the same extent.

Alcohol is a known brain toxin, particularly to the cerebellum, which is the part involved in involuntary tremor, say the authors.

Paradoxically, alcohol is often used to relieve symptoms in those who have already been diagnosed with essential tremor. But it may, in fact, hasten progression of the condition and worsen symptoms, they conclude.

"Population based study of baseline ethanol consumption and risk of incident essential tremor"
Online First J Neurol Neurosurg Psychiatry 2009; doi 10.1136/jnnp.2008.162701