Introduction

Alzheimer's disease (AD), the leading cause of dementia, is a progressive condition that impacts memory, thinking, and behaviour, often interfering with daily tasks as it progresses. While the exact cause of this decline in brain functioning remains unknown, there is evidence pointing to several risk factors associated with its development. These include increasing age, family history, mental disorders like depression, as well as factors linked to cardiovascular disease. While Alzheimer's is more prevalent in individuals over 65, it can also manifest earlier, known as early-onset Alzheimer’s disease.¹

Cardiovascular diseases (CVD) claim an estimated 17.9 million lives annually, making them the leading global cause of death. Cardiovascular health, which refers to the health of the heart and blood vessels, can be maintained through positive lifestyle habits such as healthy eating, regular exercise, abstaining from tobacco and alcohol, and reducing salt intake.²

The relationship between CVD and AD is linked to the intricate connection between the heart and the brain, involving neurovascular (where nerves and blood vessels travel to supply tissues with oxygen) and humoral (where hormones circulate in the bloodstream to regulate physiological processes) pathways. While research has explored the heart-brain axis, the exact connection remains unclear. However, there is evidence suggesting that CVD, along with ischaemic microvascular lesions found in the brains of Alzheimer's patients, may contribute to the development of the disease.³

Understanding Alzheimer's disease

Definition and symptoms of AD

Alzheimer's Disease (AD) is a progressive brain disorder caused by certain proteins building up in the brain, leading to neurological symptoms. Globally, out of around 55 million people diagnosed with dementia, it's estimated that 60% to 70% have Alzheimer's.⁴

The main symptom of AD is memory loss, which is often one of the earliest signs. This includes trouble remembering recent events or conversations, and it tends to worsen over time.

Other symptoms include:

• Difficulties with thinking and reasoning, especially with abstract concepts and multitasking; for example struggling with managing finances, balancing chequebooks, or making judgments and decisions, such as what to wear or when driving
• Challenges in planning and performing familiar tasks like dressing, bathing, cooking, or playing games
• Changes in personality and behaviour, including mood swings, depression, social withdrawal, or displays of anger or aggression

Risk factors for AD

AD is considered a multifactorial disease, meaning that no single factor solely causes it. Factors such as genetics, lifestyle, and environment can influence its onset.

• Age: The risk of AD and other dementias rises with age, particularly in individuals older than 85, where it becomes nearly one-third
• Sex: People assigned female at birth are at a higher risk of developing AD compared to people assigned male at birth
• Family history: Having a parent, brother, or sister with AD increases the likelihood of developing the disease
• Genetics: Less than 1% of AD cases are attributed to deterministic genes.
• Other risk factors: History of head injury, cardiovascular disease (CVD), and other health conditions such as diabetes, depression, stroke, and obesity, among others

Cardiovascular health and its importance

Importance of cardiovascular health for overall well-being

Throughout an average lifespan, the heart beats roughly 2.5 billion times, tirelessly pumping gallons of blood to every part of the body. This continuous circulation serves as the lifeline, transporting vital elements such as oxygen, nutrients, hormones, and essential cells, while efficiently eliminating metabolic waste products. The heart's rhythmic pulsation ensures the smooth functioning of various bodily processes, highlighting its indispensable role in sustaining life.

However, if the heart ceases its rhythm, critical bodily functions come to a halt, some within moments. This emphasises the heart's paramount importance in maintaining overall human function and well-being.

To safeguard cardiovascular health, adopting preventive measures is essential. Regular physical activity helps keep the heart strong and efficient, while a balanced diet provides the necessary nutrients for optimal function. Additionally, maintaining appropriate blood pressure and cholesterol levels is crucial in preventing cardiovascular diseases.

By prioritising heart health through lifestyle choices like regular exercise, a nutritious diet, and mindful management of blood pressure and cholesterol levels, individuals can significantly reduce the risk of heart-related issues and promote longevity and well-being.

Common risk factors for cardiovascular diseases

CVDs encompass a range of conditions affecting the heart and blood vessels, including coronary heart disease, cerebrovascular disease, peripheral arterial disease, aortic disease, rheumatic heart disease, and others. It is estimated that CVD is responsible for approximately one-third of premature deaths in people assigned male at birth and one-fifth of premature deaths in people assigned female at birth. Fortunately, these diseases can often be prevented through lifestyle changes.²

The risk factors for CVD include:

• High blood pressure
• Smoking and excessive alcohol consumption
• High cholesterol, which can lead to the formation of fatty deposits in the vessels, narrowing them
• Diabetes
• Physical inactivity
• Being overweight or obese
• Family history of CVD
• Ethnic background, with individuals of South Asian, Black African, and African Caribbean descent having a higher risk of developing CVD
• Unhealthy diet

Connection between Alzheimer's disease and cardiovascular health

The connection between CVD and AD has been established through observational and experimental data. Coronary artery disease correlates with amyloid beta levels, a marker of AD, indicating shared pathways between these conditions. Maintaining cardiovascular health significantly reduces the risk of leading causes of death, including coronary heart disease and AD. Despite advancements in CVD prevention, strategies for AD are far behind.⁵

Shared risk factors between AD and cardiovascular diseases

AD affects over 10% of adults aged 65 and older, with hypertension and atherosclerosis being linked to its pathogenesis. Risk factors for AD include genetic mutations, hypertension, dyslipidemia, diabetes, and hyperhomocysteinemia. Chronic hypertension adversely affects cerebral blood vessels, while dyslipidemia contributes to amyloid β protein. Diabetes increases dementia risk and alters insulin signalling, while hyperhomocysteinemia is associated with AD development.³

Inflammation plays a significant role in both CVD and AD pathogenesis. Atherosclerosis, characterised by inflammation, contributes to neurodegenerative diseases' onset and progression.⁵ Atherosclerosis and arteriosclerosis contribute to AD independently of ischaemic brain lesions or neurodegeneration, possibly through subtle reductions in microvascular perfusion and blood-brain barrier dysfunction. Traditional CVD risk factors promote amyloid accumulation in the brain, exacerbating AD.^6,7

Both AD and CVD share modifiable risk factors like smoking, lack of exercise, hyperlipidemia, and hypertension. Subclinical CVD in midlife may predict dementia in later years, especially in those with genetic predispositions.

Impact of cardiovascular health on the development and progression of AD

Lifestyle factors play crucial roles in both CVD and AD prevention. Regular physical activity reduces the risk, while smoking and hypercholesterolemia increase it. Hypertension, prevalent in older adults, has complex associations with AD, influenced by age and medication use.

Early interventions targeting modifiable risk factors can mitigate the burden of CVD and AD, emphasising the importance of primordial and primary prevention. Cross-disciplinary collaboration and advanced techniques are needed to unravel the intricate mechanisms underlying the heart-brain axis and develop effective diagnostic and therapeutic strategies for both conditions.

Lifestyle factors like diet and physical activity influence both CVD and AD risk. The Mediterranean and MIND diets show protective effects against AD, while physical activity reduces risk.

Despite progress, the relationship between CVD and AD remains complex. While both share common risk factors and molecular mechanisms, many questions regarding their aetiology and therapeutic strategies remain unanswered. Understanding these diseases' pathophysiology may lead to novel therapeutic interventions applicable to both CVD and AD.⁵

Summary

Alzheimer's disease is a progressive neurodegenerative condition affecting memory, thinking, and behaviour, with age, family history, and cardiovascular risk factors contributing to its development. Cardiovascular diseases are the leading global cause of death, with lifestyle habits like healthy eating and regular exercise crucial for maintaining heart health. The connection between CVD and AD involves shared risk factors and pathways, including inflammation and amyloid accumulation. Lifestyle interventions targeting modifiable risk factors can reduce the burden of both diseases. Despite progress, many questions remain unanswered, highlighting the need for further research to develop effective therapeutic strategies applicable to both CVD and AD. Understanding the intricate relationship between cardiovascular health and Alzheimer's disease is essential for advancing preventive and treatment approaches for these debilitating conditions.