If the threat of a heart attack is not enough to compel Americans to trade in their cheeseburgers and recliners for salmon and exercise bikes, how about mounting evidence that cardiovascular disease may greatly increase one’s risk of developing mind-destroying Alzheimer’s disease?
As scientists delve further into the twin pathologies of cardiovascular disease and dementia, they are increasingly convinced that afflictions of the heart and brain share common triggers and biochemical characteristics, including inflammation, oxidative stress, and hypoxia, an oxygen deficit caused by impaired blood flow.
Fortunately, many nutritional and botanical agents that have shown great efficacy in preventing and treating cardiovascular disease also appear to work via several important mechanisms to preserve healthy cognitive function and ward off the crippling effects of Alzheimer’s and other forms of senile dementia.
In this article, we examine the growing evidence indicating that cardiovascular disease may greatly increase one’s likelihood of developing Alzheimer’s, as well as strategies you can adopt today to safeguard the health of your heart and your mind.
Twin Afflictions of Heart Disease and Alzheimer’s
The latest data show that more than 60 million Americans suffer from some form of heart disease, including coronary artery disease, congestive heart failure, and cardiac arrhythmias (abnormal rhythms of the heart). Coronary artery disease in particular affects more than 13 million Americans.1 Although heart disease traditionally has been thought of as a “man’s disease,” nearly half of the 600,000 Americans who will die from heart disease this year are women. With its alarming growth rate and lack of a cure, Alzheimer’s disease is poised to become one of the most insidious medical problems of the twenty-first century. This devastating neurological condition progressively destroys one’s memory and ability to think. Alzheimer’s now affects more than 5 million Americans, including one of eight Americans aged 65 or older and nearly half of those over the age of 85. Someone in the United States develops Alzheimer’s every 72 seconds, and according to current projections, by 2050 a new case of Alzheimer’s disease will emerge every 33 seconds.
Alzheimer’s Destroys Memory in Multiple Ways
While scientists have not yet been able to pinpoint the exact cause of Alzheimer’s, they have been able to elucidate some of the biochemical processes that produce the hallmark mental changes characteristic of the disease. First, Alzheimer’s involves a significant decline in brain levels of acetylcholine, a neurochemical that is vitally important for memory formation and retention. Second, the disease is accompanied by an accumulation of harmful amyloid-beta deposits, or senile plaques, in the brain. Third, brain autopsies of Alzheimer’s patients show evidence of substantial oxidative damage wrought by free radicals. When energy is generated, free radicals are produced in every cell in the body, particularly brain cells; however, in Alzheimer’s disease, free radicals are produced in much greater amounts then normal, leading to significant damage to the brain. In a recent article on this topic in the Annals of the New York Academy of Sciences, the investigators concluded that “altogether, our findings emphasize the importance of . . . oxidative stress in the pathogenesis of [Alzheimer’s disease].”
Deadly Connections: Hypoxia, Amyloid-Beta, and Oxidative Stress
While researchers certainly know much more today about how Alzheimer’s affects the brain, we still do not know why this disease afflicts some people and spares others. However, groundbreaking research strongly suggests an intimate link between Alzheimer’s and cardiovascular diseases such as atherosclerosis, hypertension, and stroke.
Considerable evidence suggests that Alzheimer’s disease could be considered primarily a vascular disorder in which the brain does not receive enough blood flow to function optimally. This hypothesis is supported by numerous observations: 1) impaired blood flow to the brain can set in motion cognitive and neurodegenerative changes similar to those seen in Alzheimer’s disease; 2) medications that improve cerebral blood flow improve Alzheimer’s disease symptoms; and 3) decreased cerebral blood flow may be detectable even before symptoms of Alzheimer’s disease manifest.
A recent report in the Proceedings of the New York Academy of Sciences has shown that hypoxia- the reduction in oxygen received by the brain due to decreased blood flow- may be a “trigger” that contributes to the pathogenesis of Alzheimer’s disease. The authors of this important research have shown that hypoxia increases the activity of a gene called BACE1, which is involved in the production of damaging amyloid-beta plaques found in the brains of Alzheimer’s patients. The researchers found that hypoxia markedly increased amyloid-beta deposition and plaque formation in central neurons. Since a decrease in the amount of oxygen delivered to the brain may very well set off a cascade of events that culminates in Alzheimer’s disease, conditions like heart disease- a cause of brain hypoxia- provide a stark connection between heart disease and Alzheimer’s.
Besides increasing amyloid-beta production, hypoxic conditions in the brain also heighten levels of oxidative stress, an increase that poses serious dangers for the delicate cells of the central nervous system. Scientists believe that chronic oxidative stress may cause neuronal cell death, which ultimately manifests as the cognitive impairment and brain pathology known as Alzheimer’s disease.
Finally, hypoxia caused by heart disease may also contribute to the lower levels of acetylcholine observed in Alzheimer’s disease.
In a study of rats, researchers showed that chronic hypoxia (the same type typically seen in heart disease) induced by decreased blood flow to the brain caused a substantial drop in acetylcholine levels, as well as brain cell damage. While the theory that Alzheimer’s disease is primarily an ischemic (impaired blood flow) rather than degenerative type of brain disease is intriguing, many scientists suggest that both vascular and degenerative mechanisms contribute to the development of dementia, especially in very old age.
Cardiovascular Disease Impairs Blood Flow to the Brain
Comprising the heart and the body’s blood vessels, the cardiovascular system is responsible for carrying nutrients and oxygen to the body’s tissues and removing carbon dioxide and other wastes from them. These key functions are markedly impaired by cardiovascular diseases such as coronary heart disease, atherosclerosis, and heart failure.
The brain- a tremendous consumer of energy and one of the most metabolically active tissues in the body- may be especially vulnerable to the effects of impaired delivery of oxygen and nutrients, along with impaired removal of wastes. Hypoxia occurs when tissues fail to receive adequate oxygen. Scientists are discovering that conditions that reduce blood flow contribute to hypoxia, with potentially devastating consequences for the brain.