Smoking and dementia risk – the evidence

Smoking has been demonstrated to be a risk factor for dementia.  Two recent meta-analyses concluded that current smokers have an increased risk of any dementia, Alzheimer’s disease, vascular dementia and cognitive decline compared to non-smokers [1,2].

Former smokers were not found to be at increased risk compared to never-smokers, suggesting quitting smoking may be beneficial for dementia risk [1,2].

A recent study examined the association between a history of heavy alcohol use and smoking and age of disease onset in 685 people with Alzheimer's disease.  Heavy smoking (defined as one pack per day or more) was associated with a 2-3 year earlier onset of Alzheimer’s disease [3].

The adverse health effects of exposure to secondhand smoke are similar to those of active smoking.  There is some evidence that passive smoking may also be associated with increased risk of cognitive impairment and dementia [4].

These findings fit with other evidence of smoking as a risk factor for cardiovascular and cerebrovascular disease, stroke, increased oxidative stress, atherosclerosis and inflammation.  Smoking may affect dementia risk via its negative effects on the cardiovascular system, increasing risk for both Alzheimer’s disease and vascular dementia.  Smoking may also interact with other cardiovascular risk factors in an additive manner [1,2].

The evidence suggests that reducing the risk of dementia is another good reason for smokers to be advised to quit.

The Smoking Cessation Guidelines for Australian General Practice outline the evidence that interventions from health professionals increase rates of smoking cessation.  Identifying and documenting tobacco use, offering brief advice to quit smoking, and following up with the patient have been shown to improve patient motivation to quit and increase quit rates [5].

References

1. Anstey KJ, et al. Smoking as a risk factor for dementia and cognitive decline: a meta-analysis of prospective studies. American Journal of Epidemiology, 2007, 166:367-378.
2. Peters R, et al. Smoking, dementia and cognitive decline in the elderly, a systematic review. BMC Geriatrics, 2008, 8:36 doi:10.1186/1471-2318-8-36.
3. Harwood DG, et al. The effect of alcohol and tobacco consumption, and apolipoprotein E genotype, on the age of onset in Alzheimer's disease. Int J Geriatr Psychiatry, 2009, doi: 10.1002/gps.2372.
4. Llewellyn DJ, et al. Exposure to secondhand smoke and cognitive impairment in non-smokers: national cross sectional study with cotinine measurement. BMJ, 2009, 338: b462. doi: 10.1136/bmj.b462
5. Zwar N, et al. Smoking cessation guidelines for Australian general practice. 2004, Australian Government Department of Health and Ageing, Canberra.