What you need to know
- 1.18(i–ii)Interpreting total cholesterolA lipid found in cell membranes. High levels of LDL cholesterol in the blood are a risk factor for atheroma., LDLLow-density lipoprotein. It carries cholesterol from the liver to the tissues. High LDL is linked to atheroma. and HDLHigh-density lipoprotein. It carries cholesterol from the tissues back to the liver. High HDL is linked to lower risk of CVD. data; evidence of causationWhen a change in one variable directly causes a change in another. Showing it needs controlled experiments or a known mechanism..
- 1.19Diet, BMIBody mass index: body mass in kg divided by the square of height in m. It is a rough indicator of obesity. and waist-to-hip ratioWaist circumference divided by hip circumference. A high ratio shows fat stored around the abdomen. in reducing coronary heart disease risk.
- 1.12Diet as a cardiovascular risk factorSomething that increases the probability of developing a disease, without making it certain..
All measurement examples are fictional adults. This lesson does not ask for students’ body measurements or apply adult categories to children.
By the end, you should be able to…
- Distinguish cholesterol from its lipoprotein carriers.
- Evaluate evidence linking LDL to CVD.
- Calculate BMI and waist-to-hip ratio and explain their limitations.
Build your understanding
Cholesterol travels in lipoproteins
cholesterolA lipid found in cell membranes. High levels of LDL cholesterol in the blood are a risk factor for atheroma. is needed for membranes and as a precursor for some molecules; it is not simply a waste substance. Because lipids do not dissolve readily in plasmaThe liquid part of blood: water carrying dissolved substances such as glucose, ions, hormones and proteins., they are transported in lipoprotein particles. LDLLow-density lipoprotein. It carries cholesterol from the liver to the tissues. High LDL is linked to atheroma. and HDLHigh-density lipoprotein. It carries cholesterol from the tissues back to the liver. High HDL is linked to lower risk of CVD. are different carrier particles, not two chemically different kinds of cholesterol.
LDL delivers cholesterol to tissues and can contribute to cholesterol accumulation in arteryA vessel that carries blood away from the heart at high pressure. It has a thick wall with elastic fibres and smooth muscle. walls when present at elevated levels. HDL participates in transport of cholesterol back towards the liver. Lower HDL levels may be associated with higher risk, but an association does not show that simply raising HDL by any method will prevent disease.
The case for a causal role of LDL
Observational studies associate higher LDL with greater CVD risk. Inherited disorders that raise LDL are associated with earlier disease; genetic evidence and trials of LDL-lowering treatments provide additional support. Agreement among different kinds of evidence is stronger than a single correlationA relationship in which two variables change together. A correlation does not prove that one causes the other..
Interpret total cholesterol alongside LDL, HDL and the other risk factorSomething that increases the probability of developing a disease, without making it certain. supplied. Total cholesterol alone does not describe the distribution among carriers. Avoid concluding that two people with the same total cholesterol necessarily have the same risk.
Diet and body-fat distribution
Replacing saturated fats with unsaturated fats can lower LDL; the replacement nutrient matters. Sustained energy intake exceeding expenditure can increase body-fat stores, while high salt intake can contribute to raised blood pressureThe pressure that blood exerts on the walls of the blood vessels. in susceptible people. These are pathways linking diet to risk, not proof that one food alone determines an outcome.
Body mass index = mass in kilograms ÷ height in metres squared. It is an indicator based on body size, not a direct measurement of fat or a diagnosis. It does not distinguish fat from muscle or describe fat distribution.
waist-to-hip ratioWaist circumference divided by hip circumference. A high ratio shows fat stored around the abdomen. = waist circumference ÷ hip circumference, using the same units. It provides information about central fat distribution. Measurement technique, age and populationAll the individuals of one species living in one area at the same time. affect interpretation. Use supplied categories when a question requires classificationSorting organisms into groups based on shared features and evolutionary relationships.; do not diagnose from one number.
Make your reasoning visible
Square the height in metres
For a fictional adult of 81 kg and 1.80 m: BMIBody mass index: body mass in kg divided by the square of height in m. It is a rough indicator of obesity. = 81/(1.80²) = 25 kg m⁻². Dividing by height without squaring gives the wrong measure.
Evaluate indicators
BMI and waist-to-hip ratioWaist circumference divided by hip circumference. A high ratio shows fat stored around the abdomen. estimate different aspects of body size. Explain what each misses rather than treating either as a complete assessment of health.
Avoid this misconception
The claim: HDLHigh-density lipoprotein. It carries cholesterol from the tissues back to the liver. High HDL is linked to lower risk of CVD. is “good cholesterolA lipid found in cell membranes. High levels of LDL cholesterol in the blood are a risk factor for atheroma.” and LDLLow-density lipoprotein. It carries cholesterol from the liver to the tissues. High LDL is linked to atheroma. is “bad cholesterol”, so cholesterol itself exists as two kinds.
The correction: HDL and LDL are lipoprotein carriers. The cholesterol molecule is the same; carrier levels and functions differ.
Check your understanding
Try each question before opening the suggested answer.
Practice question
Retrieval and explanation · suggested answer
A fictional adult has a waist of 84 cm and hips of 100 cm. Calculate waist-to-hip ratio.
Show suggested answer
84/100 = 0.84. The ratio has no units because the matching units cancel.
Practice question
Retrieval and explanation · suggested answer
Why is a randomised trial that lowers LDL stronger evidence of causation than one observational correlation?
Show suggested answer
The intervention precedes the measured outcome and random allocation reduces systematic confounding. A reduction in cardiovascular events supports causation, particularly alongside genetic and mechanistic evidence.
Take the idea further
Apply the same specification knowledge to an unfamiliar problem. Any extra assumptions are supplied in the question.
Stretch question
Two fictional adults have the same BMI but different waist-to-hip ratios. Can their cardiovascular risks be assumed identical?
Show a hint
Consider distribution and other risk factors.
Explore the reasoning
No. Their body-fat distribution may differ, and BMI does not distinguish muscle from fat. Smoking, blood pressure, lipid levels, age and other factors can also differ. Neither measure alone establishes overall risk.
Recall this lesson
Lesson recall questions
Question 1 of 5: How can inactivity raise CVD risk even if body mass is unchanged in a fictional adult?
CVD risk factors
Practice question
Retrieval and explanation · suggested answer
How can inactivity raise CVD risk even if body mass is unchanged in a fictional adult?
Lesson: 1C 3: Risk Factors for Cardiovascular Disease
Try this from memory first.
Put your biology to work
Explore where these ideas appear in the world. Enrichment, not extra required recall.
Can a single number describe health?
1C · Diet and Cardiovascular HealthCDC describes BMI as a screening measure that needs interpretation alongside other information. This is useful when evaluating apps and social-media posts that turn a single number into…Specification 1.19Read & use the scienceClose article
Why this matters
CDC describes BMI as a screening measure that needs interpretation alongside other information. This is useful when evaluating apps and social-media posts that turn a single number into a complete health judgement. BMI combines mass and height, but does not directly measure fat distribution, muscle mass or cardiovascular function. For children and teenagers, interpretation also depends on age and sex; adult thresholds should not simply be applied to an A-level class. In population research, a simple measure may reveal useful patterns while giving incomplete information about an individual. The lesson is to identify what a measurement captures and what it misses, without turning a classroom calculation into a personal health judgement.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.19 understand how people use scientific knowledge about the effect of diet, including obesity indicators, such as body mass index and waist-to-hip ratio, exercise and smoking to reduce their risk of coronary heart disease
Use the science
What is missing from a claim that two people with equal BMI must be equally healthy?
Explore a possible response
Information about body composition, fat distribution, cardiovascular measurements and other risk factors. Equal BMI is not equal health.
Explore the source
High cholesterol can run in a family
1C · Diet and Cardiovascular HealthFamilial hypercholesterolaemia is an inherited condition in which the body’s handling of cholesterol leads to high LDL cholesterol. It challenges the assumption that a person’s appearance or lifestyle…Specification 1.12 · 1.18(i) · 1.18(ii) · 1.19Read & use the scienceClose article
Why this matters
Familial hypercholesterolaemia is an inherited condition in which the body’s handling of cholesterol leads to high LDL cholesterol. It challenges the assumption that a person’s appearance or lifestyle reveals their cardiovascular risk. Studying inherited changes that affect cholesterol regulation also helps researchers investigate whether LDL is merely associated with disease or contributes causally to it. For students, this brings together genes, lipid transport and evidence. A useful assessment must consider measured LDL, family history and other factors rather than treating BMI as a complete answer. The condition also illustrates why a mechanism can inform screening of relatives.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.12 know how factors such as genetics, diet, age, gender, high blood pressure, smoking and inactivity increase the risk of cardiovascular disease (CVD)
- 1.18(i) be able to analyse data on the possible significance for health of blood cholesterol levels and levels of high-density lipoproteins (HDLs) and low-density lipoproteins (LDLs)
- 1.18(ii) know the evidence for a causal relationship between blood cholesterol levels (total cholesterol and LDL cholesterol) and cardiovascular disease (CVD)
- 1.19 understand how people use scientific knowledge about the effect of diet, including obesity indicators, such as body mass index and waist-to-hip ratio, exercise and smoking to reduce their risk of coronary heart disease
Use the science
Why might a physically active person with a low BMI still have high cardiovascular risk associated with LDL cholesterol?
Explore a possible response
An inherited change can impair cholesterol regulation or removal independently of those indicators. BMI and activity do not measure LDL or eliminate genetic risk.