Patients with a body mass index (BMI) of 30 or higher (obese) during middle age had twice the risk of developing a degenerative neurological disease, according to a study they reported in the October issue of the Archives of Neurology. Yet a BMI between 25 and 30 (overweight) did not increase the risk.
Other bad-news markers included a systolic blood pressure of 140 mm Hg or more and total cholesterol levels exceeding 251 mg/dL Each individually doubled the risk for dementia and Alzheimerâ€™s disease.
â€œClustering of these vascular risk factors at midlife increased the risk of dementia and Alzheimerâ€™s disease in an additive manner so that persons with all three risk factors had around a six times higher risk for dementia than persons with no risk factors,â€ wrote the research team led by Mila Kivipelto, M.D., Ph.D., at the Karolinska Institute here.
A â€œhigh BMI can serve as a useful indicator of the increased risk of dementia,â€ the authors wrote. The findings, they said, add to the growing body of evidence linking vascular conditions and dementia and also introduce a high BMI as another potential risk factor. Dr. Kivipelto and colleagues noted that measuring patientsâ€™ BMI is cheap, easy, and could prove a useful screening tool.
The results were derived from the Cardiovascular Risk Factors, Aging, and Dementia (CAIDE) study, a series of four random, population-based surveys carried out during the 1970s and 1980s.
From these four surveys, the researchers studied 900 women and 549 men in 1998 who had been followed for an average of 21 years. At the time of their midlife examination, the participantsâ€™ mean age was 50.6, while at follow-up their mean age was 71.6.
At midlife, one-third of the 1,449 patients had a normal BMI that was 25 or lower. Half the group had a BMI of 25 to 30 (overweight), and 16% had a BMI of 30 or more (obese).
When the patients were re-examined, the investigators found that even after adjusting for sociodemographic variables, a BMI of 30 or higher was associated with an almost two-and-a half times greater risk for dementia and Alzheimerâ€™s (odds ratio, 2.45 [95% confidence interval, 1.2-5.1]).
The association was somewhat modified to about twice the risk for dementia after taking into account high cholesterol, midlife blood pressure, and smoking (OR, 2.1 [95% CI, 1.0-4.6]) and also after adjusting for the presence of the apolipoprotein E gene and a history of vascular disorders (OR, 1.9 [95% CI, 0.8-4.6]).
Analyzing other risks independent of obesity, the results showed a systolic blood pressure greater than 140 mm Hg correlated with almost double the dementia risk (OR, 1.97 [95% CI, 1.03-3.77]) compared with a systolic reading below 140.
A total cholesterol level of more than 251 mg/dL was also a significant risk factor (OR, 1.89 [95% CI, 1.02-3.49]). Gender and education were no-shows.
Although midlife obesity proved to be significant, Dr. Kivipelto and colleagues noted that obesityâ€™s effects on dementia risk â€œmay be partly mediated through other vascular factors.â€
However, they added, â€œthis does not mean that body weight control should be viewed as less important. On the contrary, lowering BMI has beneficial effects on a range of other risk factors, and thus, one could hypothesize that it may prevent dementia more than estimated from analyses of BMI alone.â€
As the authors point out, this study cannot establish that midlife weight loss will lower the risk of dementia and further prospective studies need to be performed.
Zalman S. Agus, MD Emeritus Professor
University of Pennsylvania School of Medicine