Smoking may be deadly but it does not cause Alzheimer’s, a new study has found.
It has been proven that tobacco smoking increases the risk for cancer, heart disease, diabetes and even blindness.
Previous studies have described smoking as a modifiable risk factor for the incurable disease.
But a new study by the University of Kentucky’s Sanders-Brown Center on Aging demonstrated that smoking is not associated with a higher risk of dementia.
The findings were based examining the risk of dementia associated with lifetime smoking on 531 individuals who did not have any cognitive impairment at the start with a high prevalence of current and former smoking.
Previous studies have described smoking as a modifiable risk factor for the incurable disease. But a new study by the University of Kentucky found smoking does not increase risk of dementia (file image)
Dr Erin Abner, an associate professor, said: ‘To be clear, we are absolutely not promoting smoking in any way.
‘We’re saying that smoking doesn’t appear to cause dementia in this population.’
Explaining how previous studies may have led to the conclusion she added: ‘The underlying data (in those studies) was solid, but the analysis didn’t take into account the idea of competing risk of mortality, which we felt was an important factor to consider in this case since smoking is so strongly associated with earlier death.
She added competing risk is a complicated concept which can change how data is ‘counted’ in a study and ultimately change study conclusions.
Dr Abner said: ‘If, for example, we were studying cancer deaths and smoking, and one of the people in the study died from heart disease, what do we do with that person’s data?’
‘That person can’t possibly die from cancer since a competing event (death from heart disease) has occurred.
‘If we ignore that information, the data are not telling the right story’
‘In the case of our study, if smoking kills someone before they show signs of dementia, how can you accurately count that person?
‘We think that those deaths should be accounted for when predicting dementia risk.’
The study examined longitudinal data from the 531 initially cognitively-normal people who were part of the SBCoA BRAiNS study, which has followed hundreds of volunteers an average of more than 11 years to explore the effects of ageing on cognition.
The mean age at enrollment was 73.2 and nearly two thirds – 63.1 per cent – were women and highly educated.
It used a statistical method called Competing Risk Analysis to determine whether there was a connection between smoking and dementia once the competing risk of death was included.
The data demonstrated that smoking was associated with a risk of earlier death, but not for dementia.
Dr Abner said: ‘Most importantly, we had sufficient numbers of events (111 incident dementia diagnoses versus 242 deaths without dementia) to make the case that smoking was a risk for earlier death but not for dementia.
‘Large autopsy numbers – 302 – were used to support this finding since pathology shows that a smoking history was associated with a lower probability of Alzheimer’s disease or other neuropathology at death.
‘These results were further supported by our analysis of causes of death, which showed that smokers tended to die of causes of death that were not associated with dementia.
‘The top two reported causes of death (heart disease and cancer) were dominated by smokers (64.2 percent of deaths due to these causes were among smokers).
‘Where cause of death was reported, consistent with the smoking literature, heart disease and cancer accounted for 56.0 percent of deaths among those who died without dementia but only 27.7 percent of those who died with dementia.
‘The conclusion that smoking did not increase the incidence of dementia, or cognitive impairment more generally, conflicts with the results of prior studies.
‘In conclusion, this study shows that when adjusted for the competing risk of death without dementia, smoking was not associated with increased risk of dementia or Alzheimer’s disease pathology in a cohort with high prevalence of lifetime smoking.
‘This may have implications for the current focus on smoking cessation as a modifiable risk for dementia.
‘We emphasize that this is not to say that efforts invested in smoking cessation are misguided or unimportant, since smoking clearly increases the risk of multiple other chronic diseases, including cardiovascular disease and cancer, as well as earlier mortality.
‘However, smoking cessation efforts focused on preventing dementia may not provide the expected benefit at the population level.’
The exact cause of Alzheimer’s is not clear. Doctors recommend stopping smoking, cutting down on drinking, eating healthier and exercising, to reduce the risk or delay the onset of dementia.
Dr Abner said their conclusions support several earlier neuropathological studies, which did not find that Alzheimer’s disease pathology was more prevalent in smokers.
She also noted that while Competing Risk Analysis is well-known and has been adapted successfully in other areas of research, it is not the standard approach in the field of dementia research, where the competing risk of death is ever-present.
She said: ‘While our study results could influence smoking cessation policy and practice, we feel that the most important consequence of our work is to demonstrate how this method could change the way we approach dementia research and to advocate for its adoption in the appropriate areas of study.’
The study was published in the Journal of Alzheimer’s Disease.