Researchers at the Karolinska Institute, Sweden's leading medical research centre, looked at the medical and death records of sets of Swedish twins, in which one smoked and the other did not.

 

"Many studies have shown a protective effect of cigarette smoking on Parkinson's disease," said the study published online this month by the Annals of Neurology - but many have argued that this may have been due to genetic factors.

 

Studying twins

 

By studying twins with different lifestyles, the researchers said they sought to exclude the genetic factor.

 

They found no association between Parkinson's disease, a degenerative neurological condition, and alcohol, coffee or place of residence.

 

But smokers appeared to be less affected, which the researchers said confirmed the protective effect of smoking on Parkinson's disease and established that the association "is only partially explained by genetic and familial environmental factors".