TUESDAY July 1, 2008 (foodconsumer.org) -- Low levels of high density lipoproteins (HDL) or the good cholesterol in middle age may raise risk of memory loss and lead to dementia later in life, a new study suggests.

The study of 3,673 participants showed falling levels of HDL cholesterol was associated with declining memory by age 60.

The findings were reported in Arteriosclerosis, Thrombosis and Vascular Biology: Journal of the American Heart Association.

The WhiteHall II study began in 1985 and was meant to examine long-term health of more than 10,000 British Civil servants working in London.

"Memory problems are key in the diagnosis of dementia," said Archana Singh-Manoux, Ph.D., lead author of the study and Senior Research Fellow with the French National Institute for Health and Medical Research (INSERM, France) and the University College London in England.

"We found that a low level of HDL may be a risk factor for memory loss in late midlife. This suggests that low HDL cholesterol might also be a risk factor for dementia."

For the study, researchers measured lipid levels in blood samples collected after an eight hour fast or at least four hours after a light fat-free breakfast.   And participants were tested for their short-term verbal memory.

The researchers found at age 55 participants with low HDL cholesterol (less than 40 mg/dL) were at a 27 percent increased risk of memory loss compared to those with high HDL (more than 60 mg/dL).   At age 60, the risk was raised to 53 percent.

During a five-year span between phases 5 and 7 of the study, participants with decreasing HDL had a 61 percent increased risk of decline in their ability to remember words compared to those with high HDL.

High levels of HDL cholesterol have been linked to lower risk of heart attacks. HDL is believed to help control the formation of beta-amyloid, the major component for plaques found in the brains of Alzheimer's patients who have a memory problem.

"It is possible that HDL cholesterol prevents formation of beta-amyloid," Singh-Manoux said.

"HDL could also affect memory through its influence on atherosclerotic disease and stroke, or vascular injury. Finally, HDL cholesterol may influence memory through its anti-inflammatory and antioxidant effects.

A foodconsumer.org health observer cautioned that the study merely revealed an association between levels of HDL cholesterol and risk of memory loss, meaning that lower HDL levels could be a biomarker rather than the cause for the condition.

Anatol Kontush, Ph.D. and M. John Chapman, Ph.D., D.Sc., at INSERM and University Pierre and Marie Curie in Paris, France, cites trial results in an accompanying editorial to suggest that "we should remain cautious when proposing therapeutic intervention on the basis of observational studies which do not allow causation to be inferred."

Eliminating trans fats and reducing intake of all fats from the diet may raise HDL cholesterol, according to the American Heart Association.   Trans fat is known to lower HDL cholesterol.  Is it possible that trans fat is partially responsible for memory loss.