Low levels of high-density lipoproteins (HDL)
- the "good" cholesterol - in middle age may increase the risk of memory loss
and lead to dementia later in life, researchers reported in Arteriosclerosis,
Thrombosis and Vascular Biology: Journal of the American Heart Association.
Observing 3,673 participants (26.8 percent women) from the Whitehall II study,
researchers found that falling levels of HDL cholesterol were predictors of
declining memory by age 60. Whitehall II, which began in 1985, is long-term
health examination 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."
Researchers defined low HDL as less than 40 mg/dL and high HDL as 60 mg/dL or
higher. The team compared blood-fat and memory data collected in phases 5 (1995)
and 7 (2002) of Whitehall II, when the average ages of the study members were 55
and 61 years, respectively.
Researchers measured lipid concentrations in blood samples collected after an
eight-hour fast, or at least four hours after a light, fat-free breakfast. They
assessed short-term verbal memory using 20 one- or two-syllable words read aloud
at two-second intervals. Study participants then had two minutes to write down
as many of the words as they could remember.
Their main findings are:
* At age 55, participants with low HDL cholesterol showed a 27 percent increased
risk of memory loss when compared to those with high HDL.
* At age 60, participants with low HDL had a 53 percent increased risk of memory
loss compared to the high HDL group.
* During the five years between phases 5 and 7, study members with decreasing
HDL had a 61 percent increased risk of decline in their ability to remember
words versus those with high HDL.
* Men and women did not differ significantly in the link between lipids and
memory loss, so researchers combined data from both sexes for analysis.
* Total cholesterol and triglycerides did not show a link with memory decline.
* Using statin drugs to raise HDL and/or lower low-density lipoprotein (LDL or
"bad" cholesterol) showed no association with memory loss.
HDL
cholesterol, which at high levels decreases the risk of heart attacks, serves
several vital biological functions. It helps clear excess cholesterol from the
blood; assists nerve-cell synapses to mature; and helps control the formation of
beta-amyloid, the major component of the protein plaques found in the brains of
Alzheimer's patients. Dementia most often occurs in people 65 years or older,
the fastest growing age group in the industrialized world.
The precise mechanism linking HDL cholesterol to dementia remains unclear. "But
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.
"Many previous investigations into the association between lipids and memory in
the elderly have focused on total or LDL cholesterol because of their status as
proven risk factors for cardiovascular disease," Singh-Manoux said. "Our results
show HDL cholesterol to be important for memory. Thus, physicians and patients
should be encouraged to monitor levels of HDL cholesterol."
In an accompanying editorial, Anatol Kontush, Ph.D. and M. John Chapman, Ph.D.,
D.Sc., at INSERM and University Pierre and Marie Curie in Paris, France, note,
"It is tempting to speculate that increasing levels of HDL-C, or "good
cholesterol" might protect our memories. However, unfortunate results in large
interventional trials with dietary antioxidants suggest that we should remain
cautious when proposing therapeutic intervention on the basis of observational
studies which do not allow causation to be inferred. Nonetheless, these studies
demand that we focus more effort on research at the interface between HDL and
brain function."
To raise HDL and lower LDL cholesterol, the American Heart Association
recommends exercising regularly; eliminating trans fats from the diet; reducing
the intake of all fats, especially saturated fats; and consuming monounsaturated
fats, such as olive, canola and peanut oils. Statins can also improve HDL and
LDL cholesterol levels, when they pose a heart risk.
Source : Medical News Today.
