Lack of 'Good' HDL Cholesterol Linked to Memory Loss

News today that low levels of the "good" HDL cholesterol raises a person's risk of memory loss and dementia may send many folks rushing to their doctor for a cholesterol check. Indeed, the findings are pretty scary. Study participants with the lowest HDL levels—defined as less than 40 mg/dL—were 53 percent more likely to perform poorly on short-term memory tests compared to those with high HDL, defined as 60 mg/dL or greater. (These healthy participants were age 61, on average, experiencing the earliest signs of dementia that typically start in middle age.) Those whose HDL levels plunged over the six-year study also experienced a decrease in the number of words they were able to recall on the memory test, says study leader Archana Singh-Manoux, senior research fellow in epidemiology at the University College London.

Video: Cholesterol: The Good and the Bad

The study, published in Arteriosclerosis, Thrombosis and Vascular Biology: Journal of the American Heart Association, underscores the dangers of allowing HDL levels to fall as you age, which often occurs with a sedentary lifestyle and expanding waistline; in fact, low HDL levels along with abdominal obesity were partially blamed for journalist Tim Russert's sudden death by heart attack, according to Michael Newman, the internist who was Russert's regular physician. The main function of HDL is to remove cholesterol from the artery wall, which reduces plaque buildup, explains cardiologist Karol Watson, codirector of the UCLA Center for Cholesterol and Lipid Management. "It also protects against oxidation and inflammation," she adds, "which can damage the vascular system that provides blood flow to the brain." Without adequate HDL, Watson speculates, blood flow may be blocked to the brain, triggering "mini" strokes that cause lingering effects like memory decline and senility similar to Alzheimer's disease.

There's currently no quick fix for low HDL levels. Statin drugs, which are great at lowering the "bad" LDL cholesterol, only modestly boost HDL. Plus, today's study found that statins had no protective effect against memory loss. The experimental HDL-boosting drug torcetrapib, which sent HDL levels soaring to above 70 mg/dL, fell by the wayside last year when it was found to cause an 80 percent spike in deaths from heart disease, cancer, and infections. Prescription niacin may be helpful at increasing HDL levels, says Watson, but many people can't tolerate the drug's side effects, which include flushing, itching, and upset stomach.

And while low HDL levels clearly are bad, having a high HDL level may not always be protective. Researchers are just learning about the complexities of HDL—how in some people, for example, it may actually fuel inflammation in the arteries and spur cardiovascular disease. Watson points to a review study she conducted showing that those with metabolic syndrome (typical in those with a large waist circumference and high glucose levels) who had naturally high HDL levels didn't lower have any lower risk of heart attacks compared with those with lower levels. "People certainly shouldn't be reassured if they're overweight and have a high HDL," Watson emphasizes.