The effect of lifestyle on some non-communicable diseases — AQA GCSE Combined Science

Incidence means the number of new cases in a population over a period. Lifestyle factors change that number. A diet high in saturated fat, salt and sugar raises the risk of obesity, type 2 diabetes, coronary heart disease and some cancers. Alcohol misuse damages the liver, causing cirrhosis, and raises the risk of some cancers and high blood pressure. Smoking damages lung tissue and blood vessels, increasing the risk of lung cancer, chronic obstructive pulmonary disease and coronary heart disease. These effects appear locally, for example in a town with many smokers, nationally in NHS statistics, and globally where tobacco or alcohol marketing is widespread. Explaining means linking the factor to a biological effect and then to a change in incidence, not just naming the disease.

A risk factor is anything that raises the chance of developing a disease, but it is not a guarantee. In non-communicable diseases, such as type 2 diabetes or coronary heart disease, risk factors act statistically across a population: groups exposed to the factor show a higher rate of disease than groups not exposed. For example, smokers show a higher rate of lung cancer than non-smokers, yet some smokers never develop it. Scientists identify risk factors by comparing disease rates between groups, often using large samples and long follow-up periods. Correlation does not prove causation, so other variables must be controlled. Understanding risk factors allows individuals to reduce risk through lifestyle choices and lets public health bodies target advice and screening.

This statement defines the categories of risk factors that increase the rate of non-communicable diseases. Risk factors can be aspects of a person's lifestyle, such as poor diet, smoking, lack of exercise, and excessive alcohol intake. Alternatively, they can be substances in the person's body or environment. Examples include asbestos fibres accumulating in the lungs, tar from smoking, or environmental exposures like air pollution. Inherited genetic factors are not included in this specific classification. Understanding these categories helps scientists identify correlations, determine causal mechanisms, and provide public health advice on disease prevention.

Lifestyle means the choices and habits a person repeats over years, and these can raise or lower the risk of non-communicable diseases such as type 2 diabetes, coronary heart disease and some cancers. Risk factors include diet high in saturated fat, salt or sugar, smoking, alcohol intake, low exercise, and obesity. These factors often interact: poor diet and inactivity can cause obesity, which increases type 2 diabetes risk. A person cannot always control risk, but changing habits can reduce it. For example, stopping smoking lowers heart disease risk over time. Scientists study large groups to link habits with disease rates, since individual cases cannot prove cause.

Risk of non-communicable disease also depends on factors inside the body or present in the environment. Inside the body, these include inherited factors such as faulty genes, hormones and chemicals produced by the body. In the environment, they include air pollutants such as particulates from burning fuels, carcinogens such as asbestos or tobacco smoke, and ionising radiation such as X-rays or gamma rays. Ultraviolet light from the Sun is non-ionising radiation, but it can still damage DNA in skin cells and increase melanoma risk. Air pollution can worsen cardiovascular and respiratory disease. Scientists use population studies to estimate how strongly each factor raises risk, because individuals vary in exposure and susceptibility.

A risk factor is anything that raises the chance of developing a disease, but a statistical link is not proof of cause. A causal mechanism is a biological explanation of how the factor produces the disease. For smoking, the mechanism is well established: tar and other chemicals in tobacco smoke are carcinogens that mutate DNA in lung cells, so smoking causes lung cancer. For diet, saturated fat raises LDL cholesterol, which is deposited in coronary artery walls, narrowing them and causing cardiovascular disease. However, for some factors the mechanism is unproven. A correlation may exist because a third variable, such as age or poverty, influences both the factor and the disease.

Cardiovascular disease (CVD) affects the heart and blood vessels. Diet high in saturated fat raises LDL cholesterol, which forms fatty plaques in coronary arteries, narrowing them and reducing oxygen supply to heart muscle, causing angina or heart attack. Smoking damages artery lining, raises blood pressure and makes platelets stickier, increasing clot risk. Regular exercise lowers blood pressure, improves cholesterol balance and helps maintain a healthy weight, reducing CVD risk. A diet rich in fruit, vegetables and unsaturated fats also lowers risk. These effects can be explained by describing how each factor changes the structure or function of blood vessels.

Obesity means carrying excess body fat, often assessed using body mass index (BMI = mass in kg ÷ (height in m)²). Type 2 diabetes is a non-communicable disease in which body cells respond poorly to insulin, so blood glucose is less well controlled. Obesity is a major risk factor: excess fat tissue, especially around the abdomen, makes cells less sensitive to insulin and increases the demand for insulin. This raises the chance of developing Type 2 diabetes, but it does not guarantee it, and not everyone with Type 2 diabetes is obese. Risk factors increase probability rather than cause disease directly. Reducing obesity through a balanced diet and regular exercise lowers the risk.

Alcohol is a recreational drug that affects many organs. In the liver, alcohol is broken down by enzymes; harmful products and long-term excess can damage liver cells, leading to fatty liver, cirrhosis and reduced liver function. This impairs roles such as detoxification and controlling blood glucose and cholesterol. In the brain, alcohol is a depressant: it slows nerve impulses and reaction times, and can impair judgement, balance and coordination. Long-term heavy drinking can cause memory problems and brain damage. The effects depend on the amount and frequency of drinking, so risk increases with sustained excess. Reducing alcohol intake lowers these risks.

Smoking introduces harmful substances into the respiratory system. Tar coats the lining of the airways and destroys cilia, so mucus and pathogens are not swept away; this causes coughing and increases infection risk. Tar also irritates the bronchi and bronchioles, causing them to narrow and produce excess mucus, which restricts airflow and leads to diseases such as chronic bronchitis. Chemicals in cigarette smoke can trigger uncontrolled cell division in the lungs, forming a malignant tumour, so smoking is a major risk factor for lung cancer. Emphysema damages alveoli, reducing the surface area for gas exchange, so less oxygen enters the blood. Because these diseases are non-communicable, they cannot be passed from person to person, but smoking greatly increases the chance of developing them.

Substances in tobacco smoke and alcohol can cross the placenta from the mother's blood into the fetus. Smoking reduces the oxygen supply to the fetus because carbon monoxide binds to haemoglobin and nicotine narrows blood vessels, so the fetus may grow more slowly and have a lower birth mass. Alcohol crosses the placenta and can damage the developing brain and other organs, leading to fetal alcohol syndrome, which may cause learning difficulties, distinctive facial features and behavioural problems. Because the fetus cannot detoxify these substances as effectively as an adult, the effects can be severe and permanent. The risk generally increases with the amount consumed, so avoiding smoking and alcohol during pregnancy reduces the chance of harm. These effects are examples of how lifestyle factors can affect health, and the resulting conditions are non-communicable.

A carcinogen is any agent that increases the chance of cancer developing by damaging DNA, so cells may divide in an uncontrolled way and form a tumour. Ionising radiation is a physical carcinogen: its high-energy waves or particles can break chemical bonds in DNA, producing mutations. Sources include X-rays, gamma rays, and radon gas. Other carcinogens include ultraviolet (UV) light (which is non-ionising), tobacco smoke, asbestos and some chemicals. Risk means probability, not certainty: exposure raises the chance of cancer but does not guarantee it, and risk generally increases with dose and duration of exposure. Students should compare carcinogens with other risk factors such as genetic inheritance, age and lifestyle choices, and explain how reducing exposure lowers risk.

Most non-communicable diseases, such as cardiovascular disease, type 2 diabetes, some cancers and chronic respiratory disease, do not have a single cause. They arise from interactions between several factors: genetic inheritance, lifestyle choices such as diet, smoking, alcohol and exercise, and environmental influences such as air pollution or exposure to carcinogens. These factors can combine, and their effects may be additive or multiplicative. For example, a person who smokes, has a high-saturated-fat diet and has a family history of heart disease may face a much greater risk than someone with only one of these factors. Because risk factors interact, it is often impossible to identify one cause, and reducing several risk factors together can lower risk more than changing just one.

Sampling means studying a subset of a population to estimate something about the whole population, such as how a lifestyle risk factor relates to a non-communicable disease. A sample must be large enough and selected without bias, for example choosing every tenth name from a list rather than only asking people in a gym. If the sample is small or biased, the estimate of risk may be unreliable. Scientists compare groups that differ in one risk factor, such as smokers and non-smokers, and look at disease rates. Correlation does not prove causation, because other factors may differ between groups. Understanding sampling lets you judge whether a claimed link between a lifestyle factor and a disease is trustworthy.

Risk-factor data often appear as tables, bar charts, line graphs or scatter graphs. Translating between forms means reading a value from a graph and writing it as a number, or plotting table values as a graph. To extract information, locate the correct axis, read the scale carefully and identify the group or category. To interpret, describe the pattern: as one variable increases, does disease risk rise, fall or stay the same? For example, a graph of daily cigarettes against lung-cancer rate may show a positive correlation. You should quote figures from the graph, compare groups and state whether the evidence supports a link. Always check units, axis labels and whether the scale starts at zero.

A scatter diagram plots one variable on the x-axis and another on the y-axis, giving one point per individual or group. If points trend upwards, the two variables are positively correlated; if downwards, negatively correlated; if there is no trend, there is no correlation. In this section the variables are often a lifestyle risk factor, such as number of cigarettes smoked per day, and a health outcome, such as incidence of lung cancer. Correlation means the variables are associated, not that one causes the other. A third factor, such as age or income, could link them, so a correlation supports but does not prove causation. You identify a correlation by describing the direction and strength of the trend, for example a strong positive correlation, and you interpret it in terms of increased risk.