Heart Disease, Stroke & Diet

British Nutrition Foundation

Cardiovascular disease (CVD) is a group of disorders of the heart and blood vessels, which includes coronary heart disease, heart attack and stroke. Approximately 26% of all deaths in the UK are due to CVD and 42,000 people die prematurely (under the age of 75) each year as a result of the disease. It is estimated 7 million people in the UK are living with CVD, which costs the NHS £6.8 billion a year. Coronary heart disease (CHD) is the leading cause of death in the UK, with around 1 person dying from CHD every 8 minutes. However, it is believed 80% of CHD and stroke could be prevented by changes to lifestyle factors, such as diet, physical activity and smoking.

Atherosclerosis is the narrowing of the arterial lumen (the space inside the artery), due to a build-up of plaque that consists of muscle cells, connective tissue, cholesterol (primarily low density lipoprotein (LDL) cholesterol) and calcium. The narrowing of the lumen restricts blood flow and if this occurs in the coronary arteries the supply of oxygen to the myocardium (muscular tissue of the heart) is deprived, causing an accumulation of lactic acid and resulting in angina (chest pain). The development of atherosclerosis starts in early life and gradually progresses throughout adolescence and early adulthood.

Risk factors for CVD

There are a number of factors which can increase or reduce the risk of CVD and the more risk factors a person has, the greater the chance of developing CVD.

Non-modifiable risk factors

  • Family historyA person is at greater risk of developing CVD if they have a family history of CVD, which is defined as:A person’s father or brother being diagnosed with CVD under the age of 55; or if a person’s mother or sister was diagnosed with CVD under the age of 65.
  • EthnicityCertain ethnic groups are at a greater risk of developing CVD; these are South Asian (Indian, Bangladeshi and Pakistani) and African Caribbean. People from a South Asian background are at a higher risk of developing CHD and, if also over the age of 65 years, are at a greater risk of having a stroke. People from an African Caribbean background are more likely to have hypertension.
  • AgePrevalence of CVD increases with age, for example, data from 2011 suggest that about 35% of men over 75 years were affected by CVD compared with about 15% of 45-64 year olds.

Modifiable risk factors

  • Socio-economic statusCompared to people living in the more affluent areas of the UK, there are on average more premature deaths (under the age of 75) from CVD in the most deprived areas of the UK.
  • SmokingSmoking is an independent risk factor for CVD and approximately 20,000 deaths from CVD each year are linked to smoking. After one year, smoking cessation reduces the risk of developing CHD by half compared to smokers and after 15 years the risk of CHD is equivalent to non-smokers.
  • Blood pressureApproximately 30% of adults in the UK have hypertension (high blood pressure), which can damage and narrow arteries or can lead to an aneurysm. Reducing blood pressure can significantly reduce the risk of CVD events, e.g. coronary heart disease, stroke and heart failure.
  • Blood cholesterol levelsElevated LDL cholesterol levels in the blood are associated with atherosclerosis and therefore this is a risk factor for CVD. A reduction of LDL cholesterol levels by 1 mmol/L can reduce deaths from CHD by 28% and CHD events by 27%.
  • Overweight/obesityBeing overweight or obese is associated with hypertension, type 2 diabetes and high cholesterol levels which are all risk factors for CVD and a person is at a greater risk of developing CVD if their BMI is greater than 25.
  • Physical activityA low level of physical activity is associated with overweight and obesity.  Meeting the current physical activity recommendations has been found to reduce the risk of CVD by 20-35%.

Dietary factors and risk of CVD

A number of dietary factors can modify the risk of developing CVD and each factor contributes to a person’s overall risk of developing disease. Diet can have both a negative and positive impact of CVD risk.

Nutrients

Fats and coronary heart disease

A high intake of saturated fatty acids can increase plasma LDL cholesterol. Current intakes in the UK exceed the recommendation of no more than 11% of food energy, for example intakes in adults aged 19-64 years are 12.7%. Studies have shown that replacing dietary saturated fatty acids with polyunsaturated fatty acids can lower the level of plasma LDL cholesterol and the total cholesterol to HDL cholesterol ratio. It has been estimated that replacing 5% of energy from saturated fatty acids with polyunsaturated fatty acids reduces the risk of developing CHD by 10%.

Evidence for the effect of replacing saturated fatty acids monounsaturated fatty acids on CHD risk has been inconclusive due to a smaller number of studies looking into this compared to those looking at polyunsaturated fatty acids but the data that is available also demonstrates a reduction in plasma cholesterol, though the effect size is smaller. National and international dietary guidelines recommend reducing saturated fatty acids in the diet and replacing with small amounts of unsaturated fatty acids.

Replacing saturated fats with wholegrain carbohydrates also appears to reduces the risk of CHD, however no effect on CHD risk is seen when saturated fat is replaced with refined carbohydrates.

Trans fatty acids

There is a strong association between trans fatty acids and an increased risk of developing CHD. This is because consumption of these fatty acids can raise LDL cholesterol and decrease HDL cholesterol. Trans fatty acids are found naturally in foods produced from ruminant animals and are also produced during the process of partial hydrogenation of edible oils.

Fibre

Diets high in fibre are associated with reduced risk of CVD. It is believed one potential mechanism for the benefit on CVD risk is the effect of fermentable fibres from foods like oats and fruit on cholesterol levels. Consumption of these types of fibre can reduce the level of total and LDL cholesterol in the blood because the amount of cholesterol absorbed in the small intestine is reduced. Additionally, as a result of the fermentation of fibre in the colon, specific short chain fatty acids are produced which have been found to inhibit cholesterol synthesis in the liver.

Salt

A high intake of salt can increase the risk of hypertension which is a risk factor for CVD. Reducing salt intake can help to lower blood pressure and therefore reduce the risk of developing CVD. It is recommended that consumption of salt should be limited to a maximum of 6g/day, however despite intakes reducing over recent years, the average intake for adults in the UK is 8g/day.

Foods

Fish

Oily fish is one of the richest dietary sources of n-3 fatty acids and it is believed its cardioprotective effects are due to the high content of the long chain polyunsaturated fatty acids DHA and EPA. Additionally, consuming fish may displace other foods such as red meat, which is typically higher in saturated fat, from the diet. Current UK recommendations are to consume 2  x 140g portions of fish per week, one of which should be oily, which would provide approximately 450mg long chain n-3 fatty acids/day, depending on which fish are chosen.

Fruit and vegetables

Meeting the current recommendation for fruit and vegetables (at least 5 x 80 g portions per day) can lower the risk of developing CVD. More recent research has started to look at fruit and vegetable subtypes to understand which specific fruit and vegetables may be most beneficial in reducing the risk of CVD. Citrus fruits and cruciferous vegetables have been found to have a positive impact on the function of the cardiovascular system but overall there isn’t enough evidence to make specific recommendations about the types for fruit and vegetables to consume.

Nuts

Consumption of nuts is associated with reduced mortality from CVD and randomised controlled trials have reported reduced levels of LDL cholesterol, something which is thought to occur due to the fatty acid composition of nuts as they are low in saturated fatty acids and high in monounsaturated fatty acids. Nuts also contain important nutrients including n-3 polyunsaturated fatty acids (especially walnuts), fibre, magnesium, potassium, vitamin E and phytochemicals. 

Stanols and Sterol

If eaten as part of a healthy balanced diet, plant sterols and stanols have been found to lower plasma LDL cholesterol levels by 7 – 12 % and in turn reduce the risk of CHD. The European Food Safety Authority (EFSA) have deemed the evidence for this reduction in cholesterol robust enough to approve a health claim. The structure of plant sterols and stanols is similar to that of cholesterol and so these compete with cholesterol for absorption in the intestine. This results in less LDL cholesterol being absorbed and instead more is taken up by the liver.

Alcohol

Previously, moderate alcohol consumption was thought to be associated with a reduction in CVD mortality, however a large body of evidence suggests the potential positive effects of moderate consumption were overestimated. Current advice that both men and women should not drink more than 14 units of alcohol per week is based on keeping health risks at a low level and a safe limit has not been set.

Dietary patterns and risk of CVD

Mediterranean diet

Observational studies have found following a Mediterranean dietary pattern to be beneficial in reducing mortality and morbidity from CVD (as well as other nutrition-related diseases e.g. cancer) and adherence to this dietary pattern has been associated with a 10% reduction in CVD incidence or mortality. A Mediterranean diet consists of:

  • a high intake of plant foods comprising mainly fruits and vegetables, cereals and whole-grain breads, pulses, nuts and seeds;
  • locally grown, fresh and seasonal, unprocessed foods;
  • large quantities of fresh fruit consumed daily whereas concentrated sugars or honey are only consumed a few times per week in smaller quantities;
  • olive oil as a main cooking ingredient and source of fat;
  • low to moderate amounts of cheese and yogurt;
  • low quantities of red meat and higher quantities of fish;
  • low to moderate amounts of red wine often accompanying main meals.

In general a Mediterranean style diet contains moderate amounts of fat which is mostly unsaturated and is high in fibre and phytochemicals.

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