Smoking History May Not Be Linked to Parkinson’s
Smoking history may not influence the severity of symptoms in Parkinson’s disease, a small study suggests.
Moreover, in some individuals, exposure to cigarette smoke may worsen motor symptoms, which could lead patients to quit smoking and explain why smoking is more common among people without the disease.
The study, “Influence of current and previous smoking on current phenotype in Parkinson’s disease,” was published in the Journal of Neurological Sciences.
Research has linked smoking with a decreased risk of developing Parkinson’s disease. The exact compound responsible for the link remains unknown, but nicotine has been put forward as a potential candidate.
Recent clinical trials, however, indicate that nicotine may not necessarily relieve the symptoms of Parkinson’s after onset of the disease.
A team of Japanese researchers now attempted to clarify the impact of a previous smoking history on a patient’s current symptoms of Parkinson’s disease. “Elucidating a suitable population that is associated with the smoking-induced clinical fluctuation in [Parkinson’s disease] would open the door to the future use of a nicotine treatment strategy,” the researchers wrote.
The study included 110 patients with Parkinson’s disease who attended a single neurology clinic between 2010 and 2018. Their mean age was 71 years, ranging from 41 to 87. The mean age at disease onset was 64 years. Most patients (84.5%) were being treated with levodopa.
Data on smoking history, motor and non-motor symptoms, and mood during exposure to cigarette smoke were collected and compared to those of an age- and sex-matched control group of 110 individuals without Parkinson’s disease.
The results showed that, compared to patients with Parkinson’s disease, current smoking was about three times as common in those without the disease (5.5% versus 15.5%).
A larger proportion of patients with Parkinson’s disease reported subjective smell loss (36.3% versus 5.5%) and severe smell loss, including the inability to smell cigarette smoke (17.6% versus 1.0%).
Among former smokers, those with Parkinson’s disease smoked fewer cigarettes daily before quitting (a mean of 16.8 versus 26.4). The proportions of former smokers and never smokers, however, were similar in the two groups.
Of note, among Parkinson’s patients who were former smokers, most (97.3%) had quit smoking prior to disease onset.
To further understand the role of smoking in the development of Parkinson’s disease, the researchers compared patients with and without a history of smoking.
In general, there were no differences between the two groups. The exceptions were the proportion of men, which was higher, and mood during exposure to cigarette smoke, which was worse in the group with a history of smoking. Furthermore, negative mood during exposure to cigarette smoke was increased over the entire life of Parkinson’s patients with a history of smoking compared to those without.
According to the researchers, “cigarette smoke-related negative mood could be a confounder for quitting smoking.”
Three (2.7%) patients with Parkinson’s reported worsening of symptoms during exposure to cigarette smoke. Two of these patients were current smokers, and one quit smoking due to difficulty in gait at eight months after the onset of Parkinson’s.
Age seemed to be a factor that could be used to discriminate between Parkinson’s patients with and without this smoking-induced deterioration. These three patients tended to be younger than those who never experienced worsening of motor symptoms due to smoking (57.0 vs. 71.4 years). Age at disease onset also seemed to be earlier in the patients with versus those without deterioration (51.0 vs. 64.7 years).
Further studies are needed to evaluate the possibility of smoking-induced worsening of motor symptoms, especially in non-elderly patients.
Although researchers noted that “it is possible that there is a neuroprotective effect of nicotine for developing PD [Parkinson’s disease],” current disease manifestations were not linked to a previous smoking history.
“Although there was only a small sample size, study results showed there was no difference in the current phenotype in PD depending on the previous smoking history. The impact of previous smoking exposure on the current neuroprotective effect after the onset will require further investigation, however, it is important to note that current results indicate that smoking could potentially promote smoking-induced deterioration in non-elderly patients,” the researchers concluded.
“These findings collectively highlight the potential target patient that could be used in future study designs,” they added.