The lower your cholesterol, the better your heart health. But a man's heart and his head don't always agree. In fact, the relationships among cholesterol levels, psychological function, and neurologic disorders are complex and sometimes controversial, reports the March issue Harvard Men's Health Watch.

There are two major forms of dementia: vascular dementia and Alzheimer's disease. Vascular dementia results when blood vessel damage deprives the brain of oxygen. Brain cells die as a result, and mental function suffers. Some studies link high cholesterol levels to an increased risk of cognitive impairment, but others report the opposite. More research is needed to sort this out, but even now, investigations of HDL (good) cholesterol and mental function have consistently reported that high HDL levels appear to help preserve mental function in older people.

The connection between Alzheimer's disease and cholesterol is even more complex. Scientists have learned much of the damage of Alzheimer's comes from deposits of a sticky protein, called beta-amyloid, in vital areas of the brain. In some studies, high cholesterol levels appear to accelerate the formation of beta-amyloid plaques. People with the genetic trait that increases the level of a particular cholesterol transport protein have a greatly increased risk of late-onset Alzheimer's.

The urgent question is whether cholesterol-lowering drugs, such as statins, can reduce the risk of Alzheimer's disease. In the most recent studies, people who took statins did not appear to be at lower risk for the disease. Additional research is under way. Right now, it is too early for firm conclusions on the relationships among cholesterol, cognitive function, and statin therapy.