Risk factors for cardiovascular diseaseEdexcel International A Level Biology: Revision notes

A risk factor is something that increases the chance of developing a disease. Some cannot be changed:

• Genetics: inherited alleles can raise LDL cholesterol, raise blood pressure or affect clotting, so a family history of CVD increases risk.
• Age: risk increases with age as damage to artery walls and plaque accumulate.
• Gender: men have a higher risk at a younger age. Before the menopause women are partly protected (oestrogen raises HDL), but their risk rises afterwards.

Smoking: chemicals in smoke damage the endothelium and start atheroma formation. Nicotine raises heart rate and constricts blood vessels, raising blood pressure. Carbon monoxide combines with haemoglobin and reduces oxygen carried. Smoking also makes platelets stickier so clots form more easily.

High blood pressure exerts a greater force on artery walls, damaging the endothelium and making plaques more likely to rupture.

Inactivity leads to weight gain, higher blood pressure and a higher LDL to HDL ratio. Regular exercise lowers blood pressure and raises HDL.

A diet high in saturated fat raises LDL cholesterol. A diet high in salt raises blood pressure. Both increase the risk of CVD.

Antioxidants (such as vitamin C and vitamin E, found in fruit and vegetables) remove free radicals. Free radicals can damage the endothelium and oxidise LDL, which makes it more likely to be taken up by macrophages to form foam cells. A diet rich in antioxidants may therefore reduce the risk of CVD, but the evidence is mixed and trials of antioxidant supplements have not all shown a benefit.

Cholesterol is carried in the blood by lipoproteins:

• LDL (low-density lipoprotein) carries cholesterol from the liver to the tissues. High LDL leads to cholesterol being deposited in artery walls (atheroma).
• HDL (high-density lipoprotein) carries cholesterol from the tissues back to the liver, so high HDL is protective.

A high total cholesterol and a high LDL:HDL ratio are associated with a higher risk of CVD. Cholesterol is measured in mmol dm⁻³.

Evidence for a causal link comes from the known mechanism (LDL is found in plaques), from studies where lowering LDL (for example with statins) reduces CVD, and from people with inherited high LDL who develop CVD young. Epidemiological data show correlation, and other factors (age, smoking) may be confounding variables.

DCPIP is a redox indicator that is decolourised when it is reduced by vitamin C (ascorbic acid). The more vitamin C a juice contains, the smaller the volume needed.

Method: put a fixed volume of DCPIP (for example 1.0 cm³) in a tube. Add juice from a burette or syringe drop by drop, mixing, until the colour just disappears (the end-point). Repeat for each juice and for a standard vitamin C solution of known concentration, until results are concordant.

Worked example: a 1.0 mg cm⁻³ vitamin C standard needs 0.80 cm³ to decolourise the DCPIP, so 0.80 mg of vitamin C reacts. A juice needs 2.0 cm³. Concentration = 0.80 ÷ 2.0 = 0.40 mg cm⁻³.

Control: same volume and concentration of DCPIP, same temperature, fresh juice, same end-point colour. Coloured juices make the end-point hard to see, so dilute or use a colour comparison.