High cholesterol, hypertension, diabetes and smoking may increase risk of dementia

High cholesterol, hypertension, diabetes and smoking have long been considered -- and aggressively treated -- as risk factors for cardiovascular disease.

These same cardiovascular (CV) risk factors in middle age may also increase significantly the risk of dementia in old age, according to Kaiser Permanente researchers. The study, of nearly 9,000 northern Californians, appears in the January 25 issue of Neurology, the scientific journal of the American Academy of Neurology.

Compared to those with no risk factors, those with two of the risk factors were 1.7 times more likely to be diagnosed with dementia. Those with three risk factors were more than twice as likely, and those with all four risk factors had a 2.37 times greater risk of being diagnosed with dementia, according to lead investigator Rachel A. Whitmer, PhD, a researcher with the Kaiser Permanente Division of Research in Oakland, California.

Correspondingly, treating one's risk factors for heart disease may also reduce the risk for dementia, said Whitmer. And earlier treatment may have an even greater benefit by virtue of the cumulative effect of longer exposure to protective therapies, she said.

Each of these four CV risk factors identified at mid-life (age 40 to 44) was associated with a 20 to 40 percent increased risk of dementia in later life. Those with diabetes were 46 percent more likely than those without diabetes to develop dementia. Similarly, those with high total cholesterol were 42 percent more likely, and those with hypertension were 24 percent more likely. Participants who reported ever smoking at mid-life were 26 percent more likely to develop dementia. The effects of cardiovascular risk factors on risk of dementia were the same across race and gender groups.

While previous studies have reported an association between individual CV risk factors and dementia, whether these risk factors in mid-life are associated with risk of dementia in older age had not been thoroughly investigated. "The real strength of our study is the large, multiethnic cohort of mid-life men and women, followed for an average of 27 years, all with equal access to medical care," said Whitmer.

Researchers studied records for Kaiser Permanente Northern California members who underwent health evaluations from 1964 to 1973 when they were between the ages of 40 and 44. Diagnoses of dementia were also obtained from inpatient and outpatient medical records.

Additional researchers include Stephen Sidney, MD, MPH, associate director for clinical research, Division of Research, Kaiser Permanente Northern California; Joseph Selby, MD, MPH, director of the Division of Research, Kaiser Permanente Northern California; S. Claiborne Johnston, MD, PhD, UCSF associate professor of neurology and epidemiology; and Kristine Yaffe, MD, UCSF associate professor of psychiatry, neurology and epidemiology. This study was funded by a grant from the National Institutes of Health.