High cholesterol is not only bad for heart, study finds

In a recent study conducted at the UC Davis Alzheimer’s Disease Center, a team of experts confirmed the relationship between unhealthy cholesterol fractions in the blood and an increased risk for Alzheimer’s disease. Led in part by Dr. Brian Reed of UC Davis, the study was the first of its kind to demonstrate the correlation between unhealthy cholesterol levels and cerebral amyloid plaque deposition in the brain. The study was published online as  “Associations Between Serum Cholesterol Levels and Cerebral Amyloidosis” on Dec. 30 in JAMA Neurology.

The study revealed that elevated circulating levels of cholesterol, specifically “bad” LDL (low density lipoprotein) cholesterol, and low levels of “good” HDL (high density lipoprotein) cholesterol, lead to the deposition of amyloid proteins in cerebral tissues; amyloid deposits are significant pathological markers for Alzheimer’s disease.

“Alzheimer’s disease is defined by a combination of clinical findings and pathology.  Clinically, the person has a dementia — a loss of multiple cognitive abilities severe enough to impair day-to-day function … this dementia is due to damage to the brain associated with amyloid plaques and neurofibrillary tangles,” said Bruce Reed, lead study author and associate director of the Alzheimer’s Disease Center.

The study itself was conducted on a diverse population of 74 men and women aged 70 years and older. The participants were recruited from California stroke clinics, support groups, senior facilities and the Alzheimer’s Disease Center itself. Of the participants, three of the recruits already suffered from mild dementia, 38 had slight cognitive impairment and the remaining 38 participants had normal cognitive function. The research team was able to measure the participants’ amyloid plaque levels by using a chemical tracer. It was confirmed that a trend of high levels of fasting LDL cholesterol (above 100mg/dL) and low levels of fasting HDL cholesterol (less than 40mg/dL) associated strongly with increased amyloid deposition in cerebral tissue.

“We have several ideas about how cholesterol levels might influence amyloid deposits.  Cholesterol in the brain plays several important roles in the production and transport of beta amyloid. Theoretically, cholesterol levels could influence the rate at which amyloid is created, or it could slow down the rate at which it is cleared from the brain,” Bruce Reed said.

Cholesterol is a hydrophobic, wax-like substance that is found in animal-derived foods; it is also produced naturally by the liver. It’s important to note that cholesterol itself is an important molecule with a myriad of biological functions and is not an antagonistic compound. Cholesterol-derived health problems arise when individuals consume it in extreme excess.

“Cholesterol’s main function in all tissues is to provide structure to cell membranes. In the liver it also undergoes its first conversion step to vitamin D. It also serves as a precursor for steroid hormones in the reproductive organs,” said Angela Zivcovic, member of the Nutrition Department faculty and part of the UC Davis Foods for Health Institute.

Some of the most common foods high in cholesterol include solid animal-fats (found in high-fat milk products, butter or lard), fatty meats (such as beef patties, and bacon), cheeses, egg yolks, non-vegan processed foods and some seafood (lobster being the most notorious). When consumed in moderation, most of the cholesterol from the diet is packaged into high or low density lipoproteins. A fraction of cholesterol is incorporated into bile and is lost through the dietary tract; this is the only way that the body may rid itself of excess cholesterol. Soluble fiber helps to expedite this necessary process by sequestering excess cholesterol in the dietary tract.

In extra-cerebral vasculature, “bad” LDL-packaged cholesterols (LDL) collide with arterial walls, causing microscopic injuries and the induction of immune response. Over time, these collisions lead to a scar-like plaque formation that remains on the arterial wall. Continuous plaque formation results in the narrowing of the arterial pathway. “Good” HDL-packaged cholesterol (HDL) helps to clear the arterial pathway by breaking up the plaque deposits and returning rampant cholesterol back to the liver. In individuals with cholesterol-derived health disorders, there are often sub-optimal blood concentrations of HDL cholesterol.

“HDL cholesterol can be difficult to raise in comparison to LDL cholesterol … but increasing physical activity does help to raise HDL levels in the blood,” said Francene Steinberg, chair of the UC Davis Nutrition Department.

The most commonly discussed consequence of unhealthy cholesterol levels are high blood pressure (due to the narrowing of the arteries), atherosclerosis (the hardening of arterial walls) and elevated risk for stroke and heart disease. As per the results of this study, Alzheimer’s disease has now joined the list.

Though the research team did not study the direct pathway by which unhealthy cholesterol levels cause amyloid plaque deposition in the brain, the confirmation that these levels are associated with amyloid plaque is a significant finding.

The typical American diet is highly conducive to a myriad of preventable health disorders. For atherosclerosis, high blood pressure, heart disease and stroke, elevated cholesterol is just the tip of the iceberg. Evidence that a disease as devastating and challenging as Alzheimer’s is a cholesterol-related health problem proves once again that significant steps should be taken to improve dietary choices and key lifestyle factors in individuals who are, or who may one day be, at risk. High-fiber, low-fat diets and regular physical activity are highly effective natural remedies that may help to mitigate preventable health disorders.