CARDIOVASCULAR DISEASE RISK FACTORS AND THE RISK FOR ALZHEIMER’S DISEASE: WHAT CAN WE DO TO INTERVENE?

Submitted by: Patricia C. Heyn, PhD, ACRM Neurodegenerative Diseases Networking Group Executive Committee Member; PM & R Department, University of Colorado Anschutz Medical Campus, Denver, CO

Sedentary behavior, defined by the College of Sports Medicine and the American Heart Association (2007 ACSM/AHA Panel Expert) as less than 30 minutes of accumulated moderate physical activity on most days of the week, increases the risk of many chronic health conditions. Chronic condition is defined as a disease that is slow in its progress and long in its continuance. Thus, the physiological mechanisms underlying these diseases have usually been active long before a particular symptom is clinically detected. Major examples of chronic diseases are dyslipidemia, hypertension, obesity, and Type 2 Diabetes Mellitus (T2DM).

Many individuals with disabilities are affected by the devastating consequences of one or more chronic diseases, especially as they get older. Without proper intervention and treatment these individuals may then fall into a dependent state for the rest of their lives, resulting in limitations in their ability to fully benefit from rehabilitation treatments.

Obesity is one of the most common secondary complications found in individuals with disabilities. Similar to obesity in the able-bodied population, obesity in individuals with severe motor impairments is associated with numerous metabolic sequelae, including glucose intolerance, insulin resistance, hyperlipidemia, and coronary artery disease. A rising treatment to maintain and increase fitness levels as well as prevent muscle and bone degeneration in individuals with disabilities is endurance exercise training (EET) that is also one of the most effective treatments for T2DM and related cardiovascular diseases (CVDs).

Remarkably, studies of the epidemiology and pathogenesis of Alzheimer’s disease (AD) suggest a strong association with cardiovascular risk factors. This evidence suggests that many of the same risk factors that promote T2DM, CVD, hypertension, and stroke, also may aggravate, or may accelerate the development of cognitive impairment. CVD is strongly associated with the future development of T2DM36-39as well as Metabolic Syndrome (MetSyn).

MetSyn is defined as clinical manifestations of at least three cardiovascular disease risk factors: (1) hypertension, (2) hyperglycemia, (3) hypertriglycemia, (4) reduced high-density lipoprotein cholesterol, and (5) abdominal obesity. In the U.S., it is estimated that 20% of adults have MetSyn, with the prevalence approaching 50% in elderly individuals. It is most frequently seen in those who are inactive and significantly overweight (with a central or intra-abdominal distribution of adiposity) which is extremely concerning to individuals who have a sedentary-induced lifestyle due to their disability.

In addition, the incidence of MetSyn is clearly higher in the disabled population. While all of the factors associated with MetSyn are CVD interrelated, the cardinal feature is insulin resistance (IR). Both central obesity and sedentary lifestyle lead to IR (and hyperinsulinemia). IR adversely affects lipid production, increasing low-density lipoprotein (LDL), and triglyceride levels and decreasing high-density lipoprotein (HDL). These changes can lead to arterial plaque deposits and CVD.

IR also predisposes an individual to hypertension. A rising treatment to maintain and increase fitness levels as well as prevent muscle and bone degeneration in individuals with disabilities is endurance exercise training (EET) that is also one of the most effective treatments for T2DM and related cardiovascular diseases (CVDs).

Very concerning is the association between pre-exiting cardiovascular risk factors and cognitive decline, suggesting that dyslipidemia and Insulin IR should be considered a risk factor for AD and other related dementias. A large (n=10,000) 27-year prospective study noted a 74% increased risk of dementia in patients that were obese at baseline. There was a further increased risk for dementia when other CVD risk factors (hyperglycemia, dyslipidemia or hypertension) were present showing a cumulative risk factor effect. 

 In the InCHIANTI study, IR was related to cognitive decline with subcortical features and with impaired frontal cortex function. Although the presence of a subjective memory complaint is a central criteria of mild cognitive impairment, it is largely studied in the older adult population with few investigations aimed at the nature and severity of subjective memory complaints in individuals with disabilities.  Studies consistently report that individuals with MCI experience more memory complaints than controls.

Therefore, there is an opportunity for identifying early cognitive decline (MCI) in individuals with disabilities who are at higher risk of developing dementia due to their inactivity status and the presence of CVDs risk factors. MCI screening could be an important preventive concept in the rehabilitation field and it should be further investigated in individuals with disabilities, especially if they also have MetSyn and related CVDs.

This group of individuals should be under vigilant care and receive lifestyle behavior enhancement therapies (i.e. weight reduction treatment, healthy eating education, exercise and adequate access to physical activity) with the goal to intervene in the process of CVDs and the possible risk of developing Alzheimer’s type cognitive impairments. In addition EET has been showing to be an important protective factor against the development of Alzheimer’s. So, it is never too late to start a healthy lifestyle behavior and it should be part of every patient’s treatment plan.

References are available from the author upon request at Patricia.Heyn@ucdenver.edu