(HealthDay News) – Plaques in the brain linked to decreased cognition in the elderly take about 15 years to accumulate, according to a study published online Feb. 27 in Neurology.

Clifford R. Jack Jr., MD, from the Mayo Clinic in Rochester, MN, and colleagues examined 260 participants aged 70–92 years enrolled in aging or Alzheimer’s disease studies. All participants underwent two or more amyloid positron-emission tomography (PET) examinations, which included baseline amyloid PET-relative standardized uptake values (SUVR), and then, for each participant, the researchers estimated a slope representing their annual amyloid accumulation rate.

Two hundred five participants were classified as cognitively normal and 55 as cognitively impaired (47 with mild cognitive impairment and eight with Alzheimer’s dementia). The researchers found that with low baseline SUVR the rates of amyloid accumulation were low. With baseline SUVR around 2, rates increased to a maximum, above which rates declined, reaching zero at baseline SUVR above 2.7. There was an inverted U shape when rate of amyloid accumulation was assessed as a function of baseline SUVR. There was a sigmoid curve with integration relating amyloid PET SUVR to time. To travel from an SUVR of 1.5–2.5 was estimated to take an average time of approximately 15 years.

“This roughly 15-year interval where the slope of the amyloid SUVR vs. time curve is greatest and roughly linear represents a large therapeutic window for secondary preventive interventions,” the authors write.

Several authors disclosed financial ties to the pharmaceutical industry.

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