Preventing and treating cardiovascular disease (1.18, 1.15, 1.16, 1.11)
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An energy budget describes the balance between energy intake and energy expenditure.
The four main factors linked to energy expenditure are:
- Basal metabolism – energy required to maintain bodily functions at rest. This includes breathing, circulation, cell repair and brain function. The basal metabolic rate (BMR) differs between individuals.
- Thermoregulation – energy required to generate or dissipate heat in order to maintain a stable body temperature. The energy required for thermoregulation varies with external conditions.
- Digestion – energy required for the physical and chemical extraction of nutrients from food. Also referred to as the thermic effect of food. The energy required for digestion is linked to diet.
- Physical activity – energy to fuel muscle contraction during movement. Metabolic rate increases during exercise, and BMR remains elevated for some time afterwards.
Mammals have adapted to store unused energy for later use if food becomes scarce as fat (triglycerides) in adipose tissue. When energy intake exceeds energy expenditure, weight gain occurs.
If there is an excess of energy over a prolonged time, there will be an increase in body mass and body fat percentage.
Obesity is defined as excessive fat accumulation that impairs health.
Health consequences associated with obesity include:
- High blood pressure (hypertension).
- High blood cholesterol and LDL levels.
- Increased risk of Type II diabetes (insulin resistance), atherosclerosis, CVD, stroke, joint problems, and certain cancers.
The likelihood of obesity can be quantified using BMI (Body Mass Index) or waist-to-hip ratio.
Where energy expenditure exceeds energy input, there is an energy deficit and weight loss.
During an energy deficit, the body uses glycogen, then breaks down fat stores, for energy. If the deficit is prolonged, the body can resort to muscle protein breakdown to meet the required energy demands.
Energy deficits can be used productively in weight loss programs to lower BMI, increase mobility and reduce obesity. It is important that these programs consider nutritional balance alongside calorie reduction.
If energy deficits are excessive or prolonged, there can be detrimental effects on health, such as:
- loss of muscle mass
- vitamin/mineral deficiencies
- menstrual irregularities
- fatigue
- hair loss
- compromised immunity.
Cholesterol is a lipid (steroid molecule) essential for:
- Cell membrane structure (maintains fluidity).
- Synthesis of hormones (oestrogen, testosterone).
- Making bile salts and vitamin D.
Insoluble cholesterol is carried in the blood attached to soluble proteins, in the form of soluble lipoproteins.
There is a proven causal relationship between total and LDL cholesterol levels and coronary heart disease (CVD).
Many longitudinal studies follow thousands of participants over many years to track the relationship of different risk factors against the rate of CVD occurrence.
It found a strong positive correlation between LDL cholesterol and CVD risk, whereas HDL cholesterol had an inverse relationship with CVD risk.
The data suggest that, when total cholesterol levels are within a healthy range, a high HDL:LDL ratio is desirable.
There is biological evidence to support the correlation of high LDL cholesterol levels and high rates of coronary heart disease (CVD).
When the cholesterol required to compose cell membranes has been consumed, LDLs deposit excess cholesterol in the arteries. This contributes to plaque formation in atherosclerosis.
Familial hypercholesterolaemia (FH) is an inherited disorder causing very high LDL levels due to defective LDL receptors. Affected individuals develop atherosclerosis and CVD at a young age, providing strong genetic evidence that LDL directly contributes to CVD.
Interventions to reduce LDL cholesterol levels when they are too high can be:
- Statins are drugs that lower LDL cholesterol. Large clinical trials show reduced CVD incidence in statin users. This also supports a causal link as lowering LDL directly reduces disease risk.
- Dietary changes, such as replacing saturated fats with unsaturated fats.
Coronary heart disease (CHD) risks can be reduced by:
- Diet – to reduce saturated fats, increase fibre & unsaturated fats.
- Exercise – to raise HDL and lower blood pressure.
- Stop smoking – to prevent endothelial damage from vasoconstriction.
- Monitor BMI & waist:hip ratio – to intervene before onset of obesity.
- Medical interventions – such as statins, antihypertensives, anticoagulants.
Smoking increases the risk of coronary heart disease (CHD) through many different mechanisms:
- Nicotine increases heart rate and blood pressure, as well as causing vasoconstriction, leading to a higher risk of endothelial damage.
- Carbon monoxide binds to haemoglobin, reducing oxygen saturation in the blood. The heart works harder, leading to increased blood pressure and atherosclerosis.
- Other toxins damage the endothelial lining, increasing the risk of atherosclerosis.
- Smoking increases platelet stickiness, leading to a higher risk of thrombosis, which can block coronary arteries.
Cardiovascular disease (CVD) can be treated and managed using a variety of different methods, including drugs and lifestyle factors.
Lifestyle factors that can be used to manage CVD include:
- Reducing or stopping the consumption of alcohol.
- Reducing or stopping smoking.
- Eating a healthy and balanced diet.
- Maintaining a healthy BMI or waist-to-hip ratio.
- Regularly exercising.
ACE (angiotensin converting enzyme) inhibitors are a type of antihypertensive drug used to treat CVD. ACE inhibitors reduce the synthesis of angiotensin II. This causes a reduction in vasoconstriction, which reduces blood pressure.
Disadvantages of ACE inhibitors include side effects such as dizziness, coughing, abnormal heart rhythms and reduced kidney function. There are alternative medications available if a person experiences significant side effects and cannot tolerate ACE inhibitors.
Calcium channel blockers are a type of antihypertensive drug used to treat CVD. Calcium channel blockers work by reducing the amount of calcium that can enter the muscle cells lining the arteries. This reduces the ability of the cells to contract. This causes reduced vasoconstriction, which reduces blood pressure.
Disadvantages of calcium channel blockers include side effects such as dizziness, swelling in the legs, headache and constipation.
Calcium channel blockers are often not recommended for people who have heart failure or have experienced a heart attack because they can reduce heart function.
Diuretics are a type of antihypertensive drug used to treat CVD. They work by increasing the volume of urine produced by the kidneys. This lowers blood volume and therefore lowers blood pressure.
Disadvantages of diuretics include side effects such as dizziness, muscle cramps, nausea and increased urination.
Often people take a combination of antihypertensive medications, such as an ACE inhibitor and a diuretic to manage their CVD.
People with high cholesterol are at a higher risk of developing CVD. Risk factors for people developing high cholesterol include genetics and diet.
Many people with high cholesterol are prescribed drugs, such as statins, to reduce blood cholesterol levels. This reduces the risk of strokes and heart attacks.
Statins lower cholesterol by inhibiting an enzyme which is involved in the production of LDL cholesterol.
Disadvantages of statins include side effects such as headache, tiredness and muscle weakness.
Eating a healthy diet can help protect against cardiovascular disease.
Dietary changes can include:
- Energy balanced.
- Reducing cholesterol.
- Reducing salt.
- Reducing saturated fat and increasing polyunsaturated fats.
- Increasing fibre, including increasing fruits and vegetables.
Some people may be given drugs to reduce the risk of coagulation. Anticoagulants or platelet–inhibitory drugs are often prescribed to people who have experienced or are at risk of a heart attack or stroke.
Aspirin is an antiplatelet medication which prevents the platelets from sticking to each other. Other antiplatelet drugs, such as clopidogrel, may also be used to prevent platelets from sticking together.
While aspirin can be very effective, many people are unable to take aspirin due to being allergic or experiencing side effects such as worsened asthma. In these cases, other medications are usually used.
Medications which reduce the stickiness of platelets increase the risk of bleeding, such as stomach bleeds. Determining if the medication is right for someone involves weighing up the reduced risk of strokes and heart attacks with the increased risk of bleeding.
