High cholesterol levels in midlife were associated with an increased risk of Alzheimer's disease and other forms of dementia many years later, according to scientists in California and Finland, who tracked almost 10,000 men and women for four decades.
"We found an association not only with high blood cholesterol, but also borderline high levels," said study senior author Rachel Whitmer, who is a research scientist and epidemiologist at the Kaiser Permanente division of research in Oakland. Researchers at the University of Kuopio in Finland also participated in the study.
Total cholesterol levels of 240 milligrams per deciliter or higher in middle age were associated with a 66 percent higher incidence of Alzheimer's disease decades later, the researchers found.
"But that wasn't a cutoff point," Whitmer said. "Around a level of 200, the risk of Alzheimer's disease started to go up."
For those in midlife with borderline-high readings between 200 mg/dl and 239 mg/dl, the increased incidence was 52 percent, according to the study, which was published online in the journal Dementia and Geriatric Cognitive Disorders and funded by the U.S. National Institutes of Health.
The Californians in the study were more ethnically diverse than the Finnish participants, and included blacks, Latinos and Asians, but "the association between high cholesterol and dementia was the same across all ethnic groups," Whitmer noted.
The other research, reported in the August issue of the Journal of Neurology, Neurosurgery and Psychiatry, followed more than 11,000 American participants in a study of atherosclerosis, the hardening of the arteries that can lead to heart attack, stroke and other major cardiovascular problems.
Researchers from the University of Minnesota, the University of North Carolina, John Hopkins and the University of Mississippi Medical Center measured smoking, high blood pressure and diabetes among the participants from 1990-1992. They then tracked them until 2004 to see how many were hospitalized for dementia.
Smokers were 70 percent more likely to develop dementia than nonsmokers; those with high blood pressure were 60 percent more likely, and those with diabetes were twice as likely as those without diabetes to develop dementia. However, there was no link between midlife obesity and later dementia.
The idea behind the study was that "if we find risk factors for dementia, maybe we can develop new treatments, preventive programs to reduce the risk of dementia later in life," said study author Dr. Alvaro Alonso, an assistant professor of epidemiology at the University of Minnesota's School of Public Health.
Post-mortem studies of brains of people who had dementia often show damage to small arteries, he said. "Maybe there have been small strokes, which are not great enough to cause clinical symptoms, but in time can lead to dementia," Alonso said.
Measures against dementia now usually start when its first signs are detected, Alonso said. "Showing that cardiovascular risk factors earlier in life have an impact on dementia later in life gives another reason why we need to intervene with those cardiovascular risk factors," he said.
The findings of both studies "are an extension of what already has been found," said Michelle Mielke, an assistant professor of psychiatry at Johns Hopkins University, who has done research on the causes of dementia.
"Both papers really point out the need to intervene in vascular factors in midlife," Mielke said. "They are as important in the risk of dementia as they are in the risk of heart disease and stroke."