Cardiovascular disease results from the narrowing of the blood vessels which restricts the transport of blood from and to the tissues of the whole body. This reduction in blood volume to the organs can be fatal because oxygen must be continuously supplied to meet the metabolic demand.
Macrovascular complications are narrowing or complete blockage of blood vessels. They may concern:
• The main coronary artery (towards the heart). A blockage (clogged artery) can lead to coronary heart disease.
• The carotid arteries supplying the brain. Reduced blood flow can lead to cerebrovascular disease or stroke.
• The lower limbs. Restricted blood flow to the lower limbs can lead to peripheral vascular disease.
The World Health Organisation reported that in 2015, 17.7 million people died worldwide due to cardiovascular disease, accounting for 31% of the total deaths, and over 75% occurring in low-and-middle-income countries.
The shrinkage of blood vessels is a process called atherosclerosis, which is mainly caused by lifestyle factors – for example, high intake of saturated fats that result in subsequent elevation of cholesterol in the blood. Cholesterol can be categorised into two forms: its ‘healthy’ form, high-density lipoprotein (HDL) that carries cholesterol from tissues to eliminate it in the liver; and its unhealthy form, low-density lipoprotein (LDL) that carries cholesterol from the liver and small intestine to surrounding tissues. Doctors will often measure the concentration of HDL as an indicator of arterial health: 240mg/ml LDL cholesterol and 40mg/ml HDL is a risk factor.
LDL and atherosclerosis
Atherosclerosis essentially begins when inflammatory cells (macrophages) are recruited to feed the blood vessels (endothelial cells) and accumulate LDL and cholesterol to form the foam cells. The foam cells have the appearance of lipid streaks that cluster to form a fibrous plaque (atheroma) that can eventually break the diet and thus form a thrombus. In severe cases, a thrombus can completely block the arteries.
It has been clearly proven that lowering cholesterol through an appropriate diet decreases the incidence of cardiovascular disease. This has been demonstrated by the Seven Counties Study, where it was found that Mediterranean diets rich in protein and fiber, but low in saturated fat and sugars, had the best results [1]. Trans-unsaturated fats found found in cakes and margarines have been shown to inhibit the activity of healthy HDL; The British Medical Journal claims that reducing fat consumption by 1% could save 7,000 lives each year in the UK [2].
Other macrovascular complications. Cardiomyopathy is a condition involving the loss of elasticity of the heart tissue, which is essential for the recoil action and pumping of blood throughout the body, due to its irreversible thickening. This can lead to heart arrhythmia and heart valve problems that all increase the risk of related cardiovascular deaths.
Hypertension. In 90% of cases of heart disease, the individual’s blood pressure is equal to or greater than 140/90mmHg. Thus, high blood pressure is one of the major risk factors for heart disease. Risk factors can be lifetsyle, age and gender (men over 50 are at a higher risk) as well as menopause and genetic predispositions.
High blood pressure is largely influenced by over lifestyles. These ‘modifiable factors’ are listed below:
• Salt consumption greater than 10g/day
• Smoking
• Alcohol consumption greater than 20g/day
• Obesity (a body mass index greater than 30 is directly corrrelated with hypertension and insulin resistance syndrome in diabetes, so it is a major risk factor)
• Diabetes
• Lack of physical activity
• Pregnancy
• Contraceptive drugs
Symptoms usually occur later in the stages of the disease and include
• Chest pain
• Shortness of breath
• Dizziness
• Fatigue
• Weakness
• Swelling of the legs
Diabetes mellitus. Diabetes exists in two forms: type 1, which is usually a herediatary disease; and type 2, which is usually caused by environmental factors, including lifestyle. The underlying cause of type 2 diabetes is an excessive caloric intake that causes insulin resistance syndrome.
What is insulin? Insulin is a hormone that is secereted by the pancreas and is essential in controlling our blood sugar levels and storing fat in relation to our energy needs. After a meal, the blood glucose level is increased, followed by the corresponding increase in insulin seceretion. Insulin encourgaes the muscles to absorb glucose for energy use and promotes the absorption of the fat, TAG (triacylglycerols), in its storage form, which constititutes our ‘white fat’. A lack of insulin response (or even production, as is also the case for type 1 diabetics) after meals means that glucose remains high in the blood for an abnormal length of time. It also means that soluble fat levels, AGNE (non-esterified fatty acids) are not converted into their storage form, TAG.
What does that mean? High levels of glucose and NEFA in the blood lead to an overpopulation on VLDL (very low-density lipoprotein) in the liver, which increases LDL levels. An altered level of TAG and cholesterol is known as dyslipidemia. Dyslipidemia poses a huge cardiovascular risk and account for 70% of cardiovascular disease in type 2 diabetics, who are twice as likely to suffer from it as non-diabetics.
Other chronic symptoms of type 2 diabetes are:
• Diabetic ketoacidosis – a diabetic condition that can lead to a state of coma. It results from the accumulation of ketones. Ketones are the metabolic product of fats when sugar has not been used as a source of energy. This also happens after a prolonged famine. Diabetic ketoacidosis can be detected by the high acidity of urine, frequent urinination, dry mouth, thirst and fruity breath.
• Non-ketotic hyperglycemic hypersmolar syndrome (NHSHC) – this is more common in type 2 diabetics. Symptoms include thirst, fever and dryness of the skin, decreased vision, weakness on one side of the body, comatose states that may involve hallucinations. This happens when the blood sugar level is above 600mg/ml and the body tries to excrete excess urine. The colour of the urine is therefore very dark since the patient is dehydrated.
• Diabetic nephropathy – kidney disease by which prolonged high levels of sugar damage the vessels that supply the kidneys, causing deterioration of the kidneys and the filtration system. In late stages, it is noted because it causes swelling in the legs and feet (edema), but it can be detected in the early stages with the discovery of the presence of protein (albumin) in the urine.
• Diabetic neuropathy – it damages the nerves because of the high level of sugar in the blood. This damage can affect the peripheral nerves and cause weakness and numbness or tingling in the hands and feet; or affect the autonomic nervous system that controls the body system.
• Diabetic retinopathy – it can manifest itself in many ways and lead to decreased vision or total blindness. For example, it can lead to cataracts and opacification of the lens in the early stages of diabetes. Diabetics are twice as likely to develop glaucoma, as increased fluid pressure in the eye can damage the optic nerve. In addition, the blood vessels of the retina can be damaged by a high level of sugar. In the advanced stages of the disease, fluid may flow from the eye and bleeding from the centre may occur.
Neuropathy and nephropathy are associated with high blood pressure.