An analysis of published studies on the relationship between Alzheimer’s disease and smoking indicates that smoking cigarettes is a significant risk factor for Alzheimer’s disease. After controlling for study design, quality of the journals, time of publication, and tobacco industry affiliation of the authors, the researchers also found an association between tobacco industry affiliation and the conclusions of individual studies.Industry-affiliated studies indicated that smoking protects against the development of Alzheimer’s disease, while independent studies showed that smoking increased the risk of developing Alzheimer’s disease.
“For many years, published studies and popular media have perpetuated the myth that smoking is protective against the development of Alzheimer’s disease. The disease’s impact on quality of life and health care costs continues to rise. It is therefore critical that we better understand its causes, in particular, the role of cigarette smoking,” said Janine K. Cataldo, lead author of the study.
According to the Alzheimer’s Association, 5.3 million Americans currently have the disease, and that number will escalate rapidly as the baby boom generation ages. Alzheimer’s disease also triples health care costs for Americans aged 65 and older, the organization states.
The researchers reviewed 43 published studies from 1984 to 2007. Authors of one-fourth of the studies had an affiliation with the tobacco industry.
They determined that the average risk of a smoker developing Alzheimer’s disease, based on studies without tobacco industry affiliation, was estimated to be 1.72, meaning that smoking nearly doubled the risk of Alzheimer’s disease. In contrast, the team found that studies authored by individuals with tobacco industry affiliations, showed a risk factor of .86 (less than one), suggesting that smoking protects against Alzheimer’s disease. When all studies were considered together, the risk factor for developing Alzheimer’s disease from smoking was essentially neutral at a statistically insignificant 1.05.
Previous reviews of the association between smoking and Alzheimer’s disease have not controlled for study design and author affiliation with the tobacco industry, according to Cataldo. To determine if study authors had connections to the tobacco industry, the researchers analyzed 877 previously secret tobacco industry documents.
They used an inclusive definition of “tobacco industry affiliation” and examined authors’ current or past funding, employment, paid consultation, and collaboration or co-authorship on a study with someone who had current or previous tobacco industry funding within 10 years of publication.
“We know that industry-sponsored research is more likely to reach conclusions favorable to the sponsor,” said Stanton A. Glantz, a study co-author. “Our findings point to the ongoing corrosive nature of tobacco industry funding and point to the need for academic institutions to decline tobacco industry funding to protect the research process.”
References:
1. Janine K. Cataldo, et al. Cigarette Smoking is a Risk Factor for Alzheimer’s Disease: An Analysis Controlling for Tobacco Industry Affiliation. Journal of Alzheimer’s Disease, Volume 19, Number 2 / 2010. DOI: 10.3233/JAD-2010-1240
