Although poor memory in middle age has not been directly linked to Alzheimer's disease and other forms of dementia in old age, memory decline is key to the diagnosis of these conditions, lead researcher Archana Singh-Manoux, PhD, tells WebMD.
"Our research does not show a link between HDL and dementia," she says. "We looked at cognitive decline in midlife, but it may turn out that this decline is a risk factor for dementia."
HDL, LDL and Memory
Researchers have attempted to study HDL and other lipids like low-density lipoprotein (LDL), total cholesterol, and triglycerides in patients with Alzheimer's and other age-related dementias, but these studies have proven problematic, Singh-Manoux says.
"By the time people are diagnosed they have usually had the disease for many years, and the disease itself may have modified these lipid profiles," she says.
As a result, more and more researchers are focusing on potential risk factors for dementia that present long before the disease is identified.
This was the approach used by Singh-Manoux and colleagues from the University College London.
Their study included 3,673 civil servants enrolled in a British health trial, which included periodic analysis of blood lipid levels and testing for memory declines.
The data analyzed by the researchers were collected at two time periods -- when the average age of the participants was 55 and again when they were 61.
Low HDL cholesterol was defined as less than 40 mg/dL, and an HDL level of 60 mg/dL or more was considered high.
During the observation period, declines in HDL were found to be associated with corresponding declines in memory.
At age 61, study participants with low levels of "good" cholesterol had a 53% increased risk of memory loss compared to participants with high HDL levels.