In a study published Wednesday in Alzheimer's & Dementia, longitudinal data from the Framingham Heart Study (FHS) showed that high-density lipoprotein (HDL) cholesterol and triglyceride levels contributed to the risk of future Alzheimer's dementia "starting as early as age 35."

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Study details and key findings

For the study, researchers evaluated the influence of vascular risk factors on incident Alzheimer's dementia over time in participants from the FHS—a group that has been under evaluation since 1971. Researchers collected data from 4932 FHS participants, including data on lipid fractions, glucose, blood pressure, BMI, and smoking habits.

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In total, 271 participants, including 167 women and 104 men, diagnosed with Alzheimer's dementia were included in their analysis. Among those participants, 225 of them had not had any strokes, 24 of them had both Alzheimer's and a stroke, and 24 of them had mixed Alzheimer's and vascular dementia. In addition, they included 4,867 individuals who were cognitively normal as controls. People with a diagnosis of non-Alzheimer's dementia were not included in the study.

To evaluate different risk factors, researchers tested age-, sex-, and education-adjusted models for each risk factor among early adults (35 to 50 years old), middle adults (51 to 60 years old), and late adults (61 to 70 years old).

On average, follow-up periods for participants in the early, middle, and late age groups were 35.2 years, 25.8 years, and 18.5 years, respectively. As participants aged, they typically had higher triglyceride and glucose levels, higher systolic and diastolic blood pressure, and lower HDL cholesterol levels. In addition, they were more likely to receive treatment for diabetes, hypertension, and dyslipidemia.

According to Xiaoling Zhang, one of the study's co-authors from Boston University School of Medicine, the risk of Alzheimer's dementia fell by 15.4% in early adulthood, and by 17.8% in middle adulthood, for every 15 mg/dL increase in HDL cholesterol.

A 15 mg/dL increase in blood glucose during middle adulthood coincided with a 14.5% increase in Alzheimer's risk. However, triglyceride levels were only associated with Alzheimer's in the early adulthood group. Notably, researchers said these findings remained significant after they adjusted for other treatments.

Commentary

"These findings show for the first time that cardiovascular risk factors, including HDL, which has not been consistently reported as a strong risk factor for Alzheimer's disease, contribute to future risk of Alzheimer's disease starting as early as age 35," Zhang said.

"While our findings confirm other studies that linked cholesterol and glucose levels measured in blood with future risk of Alzheimer's disease, we have shown for the first time that these associations extend much earlier in life than previously thought," said Lindsay Farrer, another co-author from Boston University.

According to Farrer, the study's results are significant since "Intervention targeting cholesterol and glucose management starting in early adulthood can help maximize cognitive health in later life."

Zhang and the other co-authors cited additional supporting evidence from another study in which participants in the Framingham Offspring Study who had elevated coronary heart disease risk and metabolic syndrome exhibited lower cognitive performance at age 55.

"However, our results do not distinguish whether the influences of these risk factors on the development of Alzheimer's disease may be particularly damaging during early adulthood and midlife or reflect longer accumulated risk exposure," the co-authors noted. (George, MedPage Today, 3/25)