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You can modify the risk factors that a new study has found may lead to the steepest declines in thinking skills in middle age. The study is published in the July 15, 2020, online issue of Neurology, the medical journal of the American Academy of Neurology. At the same time, the risk factors that were not associated with cognitive decline might surprise you.

"Cardiovascular risk factors, especially high blood pressure and diabetes, become more common in midlife. We found those two risk factors, as well as smoking, are associated with higher odds of having accelerated cognitive decline, even over just a short span of five years," said study author Kristine Yaffe, M.D., of the University of California, San Francisco and a member of the American Academy of Neurology. "In other words, people with these risk factors had a greater chance of having faster cognitive decline than a group of their peers who did not smoke, or have high blood pressure or diabetes. It's encouraging to know that there are behaviors people can modify in midlife to help prevent the steepest declines in thinking and memory as they age."

The study involved 2,675 people with an average age of 50 who did not have dementia. Researchers measured their cardiovascular risk factors at the start of the study: 43% were considered obese, 31% had high blood pressure, 15% were smokers, 11% had diabetes, and 9% had high cholesterol. Participants were given thinking and memory tests at the beginning of the study and five years later. Then researchers estimated the association of the five cardiovascular risk factors with decline in their performance on the thinking and memory tests that was not defined as dementia but was faster than what was seen in a group of adults of similar ages.

Five percent of the participants had accelerated cognitive decline over five years. A total of 7.5% of those with high blood pressure had faster decline, compared to 4.3% of those who did not have high blood pressure. And 10.3% of those with diabetes had faster decline, compared to 4.7% of those who did not have diabetes. A total of 7.7% of current smokers had faster decline, compared to 4.3% of those who never smoked.

After adjusting for age, race, education and other factors that could affect the risk of cognitive decline, researchers found that people who smoked were 65% more likely to have accelerated cognitive decline, those with high blood pressure were 87% more likely and those with diabetes had a nearly three times as likely to have accelerated cognitive decline.

"Surprisingly, people who were considered obese and those with high cholesterol did not have a greater risk of cognitive decline," said Yaffe. "Other studies have shown a link between obesity and dementia, but mostly in older adults. Meanwhile, the studies that examine high cholesterol and dementia have had mixed results, so our research adds to those studies."

People who had one or two of the risk factors were nearly twice as likely to have accelerated decline than people with no risk factors. People with three or more of the risk factors were nearly three times as likely to have faster decline than those with no risk factors. Of the 1,381 people with one or two risk factors, 71 had faster decline, or 5.1%, compared to 19 of the 700 people with no risk factors, which is 2.7%, and 53 of the 594 people with three or more risk factors, which is 8.9%.

"Most public health prevention efforts focus on older adults, but our study suggests the need to look at cognitive performance across a person's life span," said Yaffe. "Middle-aged adults who have one or more cardiovascular risk factors like smoking, high blood pressure, and diabetes may be people we should be monitoring and educating on healthy lifestyle choices earlier in life."

Yaffe said a limitation of the study is that researchers were unable to measure every aspect of the participants' thinking skills, but did have sensitive tests for memory, executive function, and processing speed.