Health risks, evidence and treatment — Edexcel International AS Level Biology

Revision notes

7 short notes, in the order of the specification. Each one in short:

1. Analysing data on illness and mortality

   Illness and mortality data are compared using rates, such as deaths per 100 000 people per year, so that populations of different sizes can be compared fairly. A correlation between a factor and a disease does not prove that one causes the other, because another variable may be responsible. Different studies can give conflicting evidence.

2. Evaluating the design of studies

   A well-designed health study uses a representative sample, selected without bias, that is large enough for chance variation to have little effect. Data are valid if they measure what they claim to and control other variables, and reliable if the results can be repeated. Self-reported data, small samples and uncontrolled variables reduce the trustworthiness of a study.

3. Perception of risk

   People’s perception of risk often differs from the actual risk. Dramatic, unfamiliar or involuntary risks tend to be overestimated, whereas familiar, voluntary or long-term risks, such as diet, smoking and inactivity, tend to be underestimated. Media coverage, personal experience, enjoyment and misunderstanding of statistics all influence perception.

4. Blood cholesterol, HDL and LDL

   Cholesterol is carried in the blood in lipoproteins. Low-density lipoproteins (LDL) carry cholesterol from the liver to body tissues and, at high levels, deposit it in artery walls. High-density lipoproteins (HDL) carry cholesterol from tissues back to the liver. High LDL and total cholesterol increase CVD risk; high HDL is protective.

5. Evidence linking cholesterol and CVD

   Several lines of evidence support a causal relationship between blood cholesterol (total and LDL) and cardiovascular disease. Population studies show higher rates of CVD where blood LDL is high, people with inherited very high cholesterol develop CVD early, LDL is found in plaques, and trials show that lowering LDL reduces heart attacks and strokes.

6. Using scientific knowledge to reduce the risk of CHD

   People use scientific knowledge to reduce the risk of coronary heart disease by eating less saturated fat and salt and more fruit and vegetables, taking regular exercise and not smoking. Body mass index (mass ÷ height²) and waist-to-hip ratio are indicators of obesity, which raises risk, with a high waist-to-hip ratio showing excess abdominal fat.

7. Treatments for cardiovascular disease

   Drugs reduce the risk or effects of cardiovascular disease. Antihypertensives lower blood pressure, statins lower blood LDL cholesterol, anticoagulants reduce blood clotting and platelet inhibitors stop platelets sticking together. Each lowers the chance of heart attack or stroke but carries risks, such as dizziness, muscle pain or bleeding, so benefit and risk are weighed for each patient.