Over 1 billion people on Earth smoke tobacco. WHO figures tell us that 80% of the smoking population live in low-middle income countries, most of which are not protected by any kind of smoke-free public health legislation.

China is a particular black-spot in this regard. It has the largest tobacco smoking population in the world (350 million) and 50% of the population are exposed to environmental tobacco smoke (ETS) on a daily basis, despite numerous failed attempts from government to implement smoke-free environments.

Previous studies have shown that ETS is harmful and is linked to cancer, respiratory disease and cardiovascular disease. Recent research has also shown links between smoking and dementia, but no studies have yet linked ETS with dementia.

A new cross-sectional study has been published by a team of researchers from China, the UK and USA, which claims to have found a link between passive smoking and syndromes of dementia.

Methods

The researchers used a cluster random sampling method to select 5,921 participants from urban and rural populations in the Anhui province in China. The target population were aged ≥60 years and had lived in their area for 5 years or more.

People were studied and interviewed by skilled teams of local researchers in a series of research waves:

• Baseline data were collected for dementia syndromes (2001-3)
• Follow-up data looked at ETS exposure and dementia syndromes (2007-9)

The follow-up response rate of surviving cohort members was 82.4%.

Interviews measured the levels of ETS exposure, smoking habits and dementia syndromes. General health and risk factor questionnaires were used to measure smoking exposure and dementia was measured using the Geriatric Mental State Examination (GMS). Standard methods were also used to assess blood pressure, weight and waist circumference in all participants.

The researchers used a Cox regression model to calculate the relative risk of increased dementia syndromes among participants with ETS compared to those without.

Results

• 10.6% of study participants had severe dementia
• 14.7% had moderate dementia
• People exposed to ETS had a significantly increased risk of severe dementia (adjusted RR 1.29, 95% CI 1.05 to 1.59)
• The adjusted relative risk of severe dementia was:
  • 0.99 (95% CI 0.76 to 1.28) for >0–24 level years of exposure
  • 1.15 (95% CI 0.93 to 1.42) for 25–49 level years of exposure
  • 1.18 (95% CI 0.87 to 1.59) for 59–74 level years of exposure
  • 1.39 (95% CI 1.03 to 1.84) for 75–99 level years of exposure
  • 1.95 (95% CI 1.34 to 2.83) for ≥100 level years of exposure
• Never smokers, former smokers and current smokers were all significantly associated with severe syndromes
• No links were found between ETS exposure and body mass index, annual income, hypertension, diabetes, stroke or depression

Conclusions

The authors concluded:

Environmental tobacco smoke (ETS) should be considered an important risk factor for severe dementia syndromes. Avoidance of ETS may reduce the rates of severe dementia syndromes worldwide.

The authors claim that this is the first study to investigate the links between ETS exposure and dementia. The study highlights an association between ETS exposure and severe dementia, which appears to be dose-independent, and something that affects never smokers, former smokers and current smokers.

This is a cross-sectional study and as such can never prove a causal relationship between passive smoking and dementia. Clearly, more high quality prospective longitudinal research is needed to confirm these findings, but it seems that the case is building for further smoke-free public health campaigns to protect those at risk of dementia, particular in low- and middle- income countries where smoking levels remain high and effective public health legislation is rare.

Links

Chen R, Wilson K, Chen Y, et al. Association between environmental tobacco smoke exposure and dementia syndromes. Occup Environ Med published online October 26, 2012.

Chen R. Association of environmental tobacco smoke with dementia and Alzheimer’s disease among never smokers. Alzheimer’s & dementia : the journal of the Alzheimer’s Association 1 November 2012 (volume 8 issue 6 Pages 590-595 DOI: 10.1016/j.jalz.2011.09.231) [PubMed abstract]