Having dementia in later life more than doubles the risk of death, and this risk is independent of known midlife sociodemographic and cardiovascular risk factors, according to a new prospective historical study published in the January issue of the American Journal of Geriatric Psychiatry.
"This study is suggesting that dementia per se kills," lead author Michal Beeri, PhD, from Mount Sinai School of Medicine in New York City, told Medscape Medical News.
"Our original hypothesis was that one of the reasons why demented people die more and faster is because they have a bunch of other risk factors that increase their mortality, but we are finding that that is not the case."
The aim of the study was to compare the mortality rates of elderly patients with and without dementia and the differential association of midlife risk factors with mortality according to dementia status.
Study participants were drawn from a large study of 10,059 male Jewish civil servants who participated in the Israel Ischemic Heart Disease study, which began in 1963. In 1999 and 2000, 1713 of the surviving participants were evaluated for dementia and for midlife sociodemographic and cardiovascular risk factors, late-life dementia (dementia occurring older than age 65 years), and mortality.
During a period of 6 years, 718 of the participants died (42%); of the 307 participants with dementia, 71.8% died, and of the 1407 patients without dementia, 35.4% died.
On multivariate survival analysis, patients with dementia had a hazard ratio (HR) for mortality of 2.27 compared with patients without dementia (95% confidence interval [CI], 1.92 - 2.68). The study also found that other risk factors associated with mortality were socioeconomic status (HR, 0.94; 95% CI, 0.88 - 1.00), higher systolic blood pressure (HR, 1.16 per 20 mm Hg; 95% CI, 1.06 - 1.28 mm Hg), higher diastolic blood pressure (HR, 1.15 per 10 mm Hg, 95% CI, 1.06 - 1.25 mm Hg), and ever smoking (HR, 1.38; 95% CI, 1.18 - 1.61).
However, midlife total cholesterol was not associated with mortality.
Moreover, none of the interactions of the risk factors with dementia was significant.
"You would assume that those cardiovascular risk factors that were measured in midlife would be associated with mortality 35 years later, so people who had high blood pressure, higher systolic, low sociodemographic status, higher diastolic, and having ever smoked had higher mortality in this study, which is what everybody else has shown too," Dr. Beeri said.
"But when you try and see an interaction, whether the fact that you have high blood pressure and dementia is what is increasing your risk of death, you don't find that."
Dr. Beeri also emphasized that her study does not have information on the cause of death. She hopes that this information will be forthcoming in another upcoming study.
However, she added, this research demonstrates that "midlife risk factors associated with increasing mortality, including in our study, were not the explanation for the increased death of demented people," she said.
The fact that people with dementia are at increased risk for mortality is something that is well known and has been well known for a long time, said David Knopman, MD, professor of medicine at the Mayo Clinic in Rochester, Minnesota, who was asked by Medscape Medical News to comment on the findings.
"The diagnosis of dementia definitely has a large impact on survival. That's well known. It roughly halves survival rate in older people. The issue about this paper is that these researchers looked at midlife cardiovascular risk factors and found that there was not an interaction between the presence of the cardiovascular risk factors and dementia — that having had hypertension or diabetes or smoking in midlife didn't make the mortality rate rise or reduce the survival for dementia additionally," said Dr. Knopman, who is also deputy editor of Neurology and a fellow of the American Academy of Neurology.
The fact that dementia in and of itself is associated with a greater mortality risk has been repeatedly demonstrated in many studies.
"A clinical diagnosis of Alzheimer's disease is associated with about a halving of the survival rate. If you have vascular dementia from a stroke, and have cognitive impairment or meet criteria for vascular dementia, that's even worse in terms of survival, so this is pretty well known. I would say that this study confirms what we already know," Dr. Knopman said.
Dr. Beeri and Dr. Knopman have disclosed no relevant financial relationships