Dementia may be three times more common in people with essential tremor than in the general population, scientists have found.

The results of the study are published on the website of the American Academy of Neurology.

Essential tremor is the most common tremor disorder, occurring more often than Parkinson's disease. In addition to tremor of the arms and hands, people may experience involuntary shaking of the head, jaw and voice.

The study involved 222 people with essential tremor, with an average age of 79 at the start of the study. They underwent thinking and memory tests to determine whether they had normal cognitive abilities, mild cognitive impairment or dementia at the start of the study.

The participants then had follow-up examinations every 1.5 years for five years. Of this group, 168 had normal cognitive skills, 35 had mild cognitive impairment and 19 had dementia at the start of the study.

During the study, 59 people developed mild cognitive impairment and 41 developed dementia.

The researchers then compared the rate at which people developed mild cognitive impairment and dementia, and the prevalence of these conditions with the rates and prevalence in the general population. They also compared the participants' rates to the rates and prevalence in people with Parkinson's disease.

Researchers found that 19% of participants developed dementia during the study, and each year an average of 12% of people diagnosed with mild cognitive impairment developed dementia. These rates were three times higher than in the general population. However, these rates were lower than in people with Parkinson's disease, among whom dementia is more common.

The researchers also found that 27 per cent of participants experienced or developed mild cognitive impairment during the study, almost double the 14.5 per cent rate in the general population, but less than the 40 per cent rate in people with Parkinson's disease.