Older adults who have shifting levels of fatty compounds in the blood (cholesterol and triglycerides) may face a higher likelihood of developing Alzheimer’s disease and related dementias compared with people who have steady levels, according to a new study.Published online this week in the journal Neurology, the research adds to growing evidence suggesting a connection between dementia risk and cholesterol, per a retrospective cohort study, and triglycerides, per another study.“Routine screenings for cholesterol and triglyceride levels are commonly done as part of standard medical care,” said study author Suzette J. Bielinski, PhD, a genetic epidemiologist with the Mayo Clinic in Rochester, Minnesota, in a statement.“Fluctuations in these results over time could potentially help us identify who is at greater risk for dementia, help us understand mechanisms for the development of dementia, and ultimately determine whether leveling out these fluctuations could play a role in reducing dementia risk.”
Dr. Bielinski and her collaborators used health data from nearly 12,000 adults 60 or older (average age 71) who did not have a prior diagnosis of Alzheimer’s disease or dementia. The team then reviewed measurements of total cholesterol, triglycerides, low-density lipoprotein cholesterol (LDL or “bad cholesterol”
) and high-density lipoprotein cholesterol (HDL or “good cholesterol”
) on at least three different days in the five years before the study start.Over an average follow-up period of 13 years, 2,473 participants developed Alzheimer’s disease or another form of dementia
.Those who had the greatest swings (either up or down) in total cholesterol had a 19 percent higher risk of dementia compared with those with the least variability in these levels. Individuals with the most variation in triglyceride levels had a 23 percent greater likelihood of developing dementia.When looking specifically at fluctuations in HDL
, however, study authors did not find any link to increased dementia risk.
The Connection Between Cholesterol and Alzheimer’s DiseaseFor Hussein Yassine, MD
, an endocrinologist with Keck Medicine of USC and an associate professor of medicine with the Keck School of Medicine of USC in Los Angeles, the results are not surprising.Cholesterol and triglycerides are fats in the blood known as lipids. The brain is highly enriched in lipids, according to research
, and disruption in lipid levels has been associated with neurologic disorders as well as neurodegenerative diseases such as Alzheimer’s disease, according to Dr. Yassine, who was not involved in the study.“We’ve known that lipid metabolism [the breakdown and processing of fats] is associated with the risk of developing Alzheimer’s,” he says. “Whether they are triglycerides, HDL, or LDL, they all affect that risk. The people who fluctuate tend to be more in association with disease than people who do not fluctuate.” Yassine says that changes in diet and lack of exercise can cause lipid levels to change over time.
Previous studies have linked high levels of bad cholesterol and triglycerides to dementia, but research is conflicting. For example, this current analysis mentions evidence showing that high cholesterol in late life may be associated with decreased dementia risk.How an imbalance in lipids may affect the brain is not certain, but Yassine indicates that changes in lipid levels may contribute to insulin resistance, when the cells in your body don’t respond well to the hormone insulin and can’t easily use glucose from the blood. Insulin resistance in the body may lead to type 2 diabetes and possibly to the plaques and tangles of Alzheimer’s disease, per a past review.Another theory is that changes in lipid levels may impair blood flow in the brain.Lifestyle Changes May Help Improve Insulin SensitivityDiet and exercise are two lifestyle interventions that may improve insulin sensitivity — not only reducing dementia risk but diabetes risk as well.The Alzheimer’s Society stresses the benefits of aerobic activity, pointing to evidence that exercise to boost your heart rate may improve thinking and memory, and reduce rates of dementia in middle-aged or older adults.As far as diet is concerned, research suggests that the Mediterranean diet may help keep dementia at bay. This eating plan emphasizes plant-based foods and healthy fats. The diet often features vegetables, fruit, beans, lentils, nuts, whole grains, olive oil, and a moderate amount of fish.Whether medications may help, remains a question. Yassine notes that the study accounted for medication use, but authors found “no statistical difference in terms of those who are on medications versus those who are not.”Ultimately, the researchers recognized that more investigation is needed. “It remains unclear why and how fluctuating levels of cholesterol and triglycerides are related to the risk of Alzheimer’s disease,” said Bielinski. “Further studies looking at the changes over time for this relationship are needed in order to confirm our results and potentially consider preventive strategies.”