Lifestyle Factors and Chronic Disease Mechanisms

To provide valid data on risk factors (factors linked to an increased rate of disease), scientific studies must use excellent sampling principles. Samples must be large to minimize the effect of anomalies, random to avoid bias, and unbiased to ensure they represent the whole population accurately.

Cardiovascular Disease (CVD)

Understanding how our habits affect our blood vessels explains why many heart attacks are preventable. Coronary Heart Disease (CHD) occurs when layers of fatty material (plaques or atheromas) build up inside the coronary arteries, narrowing the lumen (the central space of the blood vessel).

Smoking and poor diet provide clear causal mechanisms for CHD. Nicotine increases heart rate and blood pressure, causing vasoconstriction, while carbon monoxide binds to haemoglobin to form carboxyhemoglobin, reducing the blood's oxygen-carrying capacity. A high-saturated fat diet increases blood cholesterol, leading to fatty deposits, and high salt intake increases blood pressure, which damages the artery lining (the endothelium).

Narrowed arteries reduce the volume of oxygenated blood reaching the heart muscle. This causes a decrease in aerobic respiration, meaning less energy is available for heart contractions. If oxygen is severely restricted, the heart muscle switches to anaerobic respiration, causing a buildup of lactic acid, muscle fatigue, and eventually cell death (a heart attack).

Comparing CVD Treatments

When evaluating treatments for cardiovascular disease, you must consider both surgical and medical interventions.

Treatment	Description	Advantages	Disadvantages
Stent	A metal mesh tube inserted to keep narrowed arteries open.	Restores blood flow immediately; long-lasting effect.	Risk of complications during surgery (e.g., bleeding, infection) and risk of blood clots near the stent.
Statin	A drug that lowers LDL ("bad") cholesterol in the blood.	Slows the buildup of fatty deposits without surgery.	Requires long-term daily compliance; can cause side effects like muscle pain or liver damage.

Obesity and Type 2 Diabetes

Your body can produce plenty of insulin but still suffer from dangerously high blood sugar. Obesity is a major risk factor for Type 2 Diabetes, a disorder where the body's cells no longer respond to insulin. This phenomenon is known as insulin resistance.

The pancreas continues to produce insulin, but the liver and muscle cells ignore the signal to take up glucose from the blood. Fat stored around the abdomen is more strongly linked to insulin resistance than fat stored elsewhere. High-carbohydrate diets cause rapid glucose spikes, which lead to insulin overproduction and eventually drive this cellular resistance.

Worked Example: Calculating Risk Factors

Doctors use mathematical models to assess the risk of developing Type 2 Diabetes based on body measurements.

Body Mass Index (BMI) Formula:

$$\text{BMI} = \frac{\text{mass (kg)}}{\text{height}^2 \text{ (m}^2)}$$

Step 1: Write down what you know.

• If a patient has a mass of $95$ kg and a height of $1.7$ m.

Step 2: Substitute into the equation.

• $\text{BMI} = \frac{95}{1.7^2}$

Step 3: Calculate the final answer.

• $\text{BMI} = \frac{95}{2.89} = 32.87$
• A BMI $> 30$ is classified as obese, indicating a high risk for Type 2 Diabetes.

Another key measurement is the Waist-to-Hip Ratio. The risk of Type 2 Diabetes increases significantly if this ratio is above $1.0$ for men and $0.85$ for women.

Alcohol: The Liver and the Brain

A quick drink might feel relaxing, but inside your body, your liver and brain are working overtime to process a toxic substance. Alcohol is a depressant that slows nerve impulse transmission in the brain, increasing reaction times. Long-term use physically damages the brain, causing atrophy (shrinking) and a loss of normal structure.

In the liver, alcohol can cause cirrhosis, a condition where healthy liver tissue is irreversibly replaced by scar tissue. This leads to metabolic failure, meaning the liver can no longer detoxify substances like ammonia, convert glucose into glycogen, or break down lactic acid after exercise.

Liver failure also severely impacts digestion because less bile is produced. Without bile, fats cannot be emulsified, resulting in a smaller surface area for lipase enzymes to work on. Alcohol is also classified as a carcinogen because it increases the risk of developing liver cancer.

Smoking and Lung Disease

Every time a heavy smoker inhales, they pull around 4,000 different chemicals into their lungs. Between 50 and 60 of these are known carcinogens, such as tar. These chemicals cause mutations in DNA, which leads to uncontrolled cell division (mitosis) and the formation of a tumour.

Chemicals in smoke also paralyse the cilia lining the respiratory tract. Because the cilia cannot waft mucus and trapped pathogens upwards, smokers develop a persistent cough and are highly prone to lung infections.

Smoking is the primary cause of emphysema, a disease where the delicate walls of the alveoli break down and fuse together. This drastically reduces the surface area to volume ratio available for gas exchange. For an ideal alveolus, the surface area is approximated by $SA = 4\pi r^2$, and any reduction in this area heavily decreases the efficiency of oxygen diffusion into the blood.

Effects of Lifestyle on the Unborn Fetus

Imagine trying to breathe through a thick straw while running—that is similar to how a fetus feels when a pregnant mother smokes. Carbon monoxide from cigarette smoke binds irreversibly to maternal haemoglobin.

Because the maternal red blood cells are carrying carbon monoxide instead of oxygen, less oxygen crosses the placenta to the fetus. The fetus is forced to carry out less aerobic respiration, providing less energy for growth and resulting in a low birth weight, premature birth, or even stillbirth.

Alcohol (ethanol) also severely impacts fetal development. It is a small molecule that acts as a teratogen by diffusing easily across the placenta, and the fetal liver is entirely unable to process it. This causes Fetal Alcohol Syndrome (FAS), which results in brain damage and physical deformities. The AQA specification mandates that there is absolutely no safe level of alcohol consumption during pregnancy.