For women, the decline in reasoning approached 5 percent for those aged 45 to 49 and about 7 percent for those 65 to 70, the researchers found.
"Greater awareness of the fact that our cognitive status is not intact until deep old age might lead individuals to make changes in their lifestyle and improve [their] cardiovascular health, to reduce risk of adverse cognitive outcomes in old age," Singh-Manoux said.
Research shows that "what is good for the heart is good for the head," which makes living a healthy lifestyle a part of slowing cognitive decline, she said.
Targeting patients who have risk factors for heart disease such as obesity, high blood pressure and high cholesterol might not only protect their hearts but also prevent dementia in old age, the researchers said.
"Understanding cognitive aging will be one of the challenges of this century," especially as people are living longer, they added.
In addition, knowing when cognitive decline is likely to start can help in treatment, because the earlier treatment starts the more likely it is to be effective, the researchers noted.
Francine Grodstein, an associate professor of medicine at Brigham and Women's Hospital in Boston and author of an accompanying editorial, said more research is needed into how to prevent early cognitive decline.
"If cognitive decline may start at younger ages, then efforts to prevent cognitive decline may need to start at younger ages," she said.
"New research should focus on understanding what factors may contribute to cognitive decline in younger persons," Grodstein added.
"This is consistent with what we have seen in other studies and the cognitive changes that occur as we age," said Heather M. Snyder, senior associate director of medical & scientific relations at the Alzheimer's Association.
These changes do not mean that all these people will go on to develop Alzheimer's d
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