The findings showed that among study subjects aged 75–84, those whose total cholesterol was higher than it was in midlife had a 50 percent higher risk of marked cognitive decline.
However, among those aged 85–94 whose total cholesterol was higher than it was in midlife, risk for marked cognitive decline happened to be 32 percent lower.
"Our results," notes first study author Jeremy Silverman, who is a professor of psychiatry at the Icahn School of Medicine at Mount Sinai in New York City, NY, "have important implications for researching genetic and other factors associated with successful cognitive aging."
He and his co-author James Schmeidler, also of the Icahn School of Medicine at Mount Sinai, report their findings in the journal Alzheimer's & Dementia.
Cholesterol serves many functions
Cholesterol is a fat-like compound that is found in all of the body's cells. It has a complex biology and serves many functions.
Although we can get cholesterol from animal-based foods such as meat, milk, cheese, and eggs, our bodies can make all the cholesterol that our cells need.
To reach all the cells of the body, cholesterol travels in the bloodstream packed inside two types of lipoprotein: low-density lipoprotein and high-density lipoprotein.
Usually, headlines about cholesterol are dominated by its relation to heart disease risk. However, the new study reveals an intriguing connection to successful cognitive aging.
Five measures of total cholesterol over time
For their analysis, the researchers examined data on 1,897 participants from the Framingham Heart Study, all of whom had healthy cognitive function when they entered the study.
They investigated associations between total cholesterol levels and incidences of marked cognitive decline that emerged during the decades of follow-up as the participants progressed through their middle and later years of life.
The researchers used five "time-dependent" measures of total cholesterol. These were:
- average at age 40 (midlife)
- average at age 77 (late life)
- average since age 40
- whether the level went up or down ("linear change since midlife")
- whether any change in level slowed down or sped up (did the linear change accelerate or decelerate?)
The results showed that some of the measures were predictive of a higher risk of marked cognitive decline.
However, the study authors also found that "[s]ome associations of cholesterol with cognition diminish as outcome age increases," and that "[i]n the oldest-old, some relationships reverse from younger elderly samples."
More specifically, they found that among the cognitively healthy members of the group aged 85–94, having had a high total cholesterol level in midlife was linked to a reduced risk of marked cognitive decline.
A biomarker of successful cognitive aging?
The findings reveal the need to look more closely at different age groups in this type of research.
They challenge, for instance, studies that have concluded that cholesterol is linked to higher risk for cognitive decline in older people — but those studies have mainly focused on adults up to the age of 75.
Prof. Silverman points out that their findings should not be taken to mean that those aged 85 and older should now seek to raise their cholesterol levels.
"We don't think high cholesterol is good for cognition at 85," he adds, "but its presence might help us identify those who are less affected by it."
"We hope to identify genes or other protective factors for cognitive decline by focusing on cognitively healthy very old people who are more likely to carry protective factors."
Prof. Jeremy Silverman