Lifestyle Changes Disease Risk at Every Scale
Definition
Non-communicable disease
A disease that cannot be spread between organisms. It is not caused by a pathogen and often develops slowly, for example from lifestyle, diet, genes or a nutrient deficiency.
- Lifestyle factors change exposure to biological risks, while social and economic conditions affect the choices available.
- Effects can be measured in individuals, local communities, countries and global populations.
Diet and Exercise Affect Body Mass
- Energy intake above energy use causes fat storage and can lead to obesity, while insufficient energy or nutrients cause malnutrition.
- Regular exercise raises energy use and improves cardiovascular fitness.
- Body mass index is calculated using BMI=mass (kg)(height (m))2\mathrm{BMI}=\frac{\mathrm{mass\,(kg)}}{\left(\mathrm{height\,(m)}\right)^2}BMI=(height(m))2mass(kg).
- BMI estimates mass relative to height but cannot distinguish fat from muscle or show where fat is stored.
- Excess energy intake increases fat storage, while diets deficient in energy, protein or micronutrients cause different forms of malnutrition.
- Waist-to-hip ratio is calculated using WHR=waist circumferencehip circumference\mathrm{WHR}=\frac{\mathrm{waist\ circumference}}{\mathrm{hip\ circumference}}WHR=hip circumferencewaist circumference, with both measurements in the same unit.
Example
- for a mass of 81 kg81\,\mathrm{kg}81kg and height of 1.80 m1.80\,\mathrm{m}1.80m, BMI=811.802=25.0\mathrm{BMI}=\frac{81}{1.80^2}=25.0BMI=1.80281=25.0.
- For an 84 cm84\,\mathrm{cm}84cm waist and 100 cm100\,\mathrm{cm}100cm hips, WHR=84100=0.84\mathrm{WHR}=\frac{84}{100}=0.84WHR=10084=0.84.
Alcohol Damages the Liver
- The liver metabolises alcohol, and repeated high intake damages liver cells.
- Fat can accumulate, followed by inflammation and irreversible scarring called cirrhosis.
- Reducing alcohol intake lowers risk, but established cirrhosis may not be reversible.
- Alcohol damages hepatocytes, promotes fat accumulation and inflammation, and repeated injury can produce irreversible cirrhosis.
Smoking Raises Cardiovascular Risk
Definition
Coronary heart disease
A disease in which fatty deposits build up in the coronary arteries, narrowing them and reducing the blood flow to the heart muscle.
- Carbon monoxide reduces the oxygen carried by haemoglobin, so the heart works harder to supply tissues.
- Nicotine raises heart rate and blood pressure, while smoke chemicals damage artery linings and promote fatty deposits and clots.
- Waist-to-hip ratio estimates central fat distribution, which is associated with greater cardiovascular and type 2 diabetes risk.
- Smoking damages artery linings, raises blood pressure, reduces oxygen transport and increases the probability of thrombosis.
Common Mistake
BMI is a screening measure, not a diagnosis, because high muscle mass, age and fat distribution affect its interpretation.
Local, National and Global Effects
- Locally, disease patterns reflect food access, income, transport, recreation space and exposure to tobacco or alcohol.
- Nationally, non-communicable disease increases healthcare costs and reduces productivity.
- Globally, urbanisation, poverty and unequal healthcare create both obesity and undernutrition in different populations.
- Population disease patterns reflect food price, advertising, working conditions, healthcare access and public-health policy as well as personal choice.
Exam technique
- Show every substitution and give the final BMI or ratio to a sensible precision.
- For lifestyle explanations, link the exposure to a named biological change and then to disease risk.
Interpret Lifestyle Evidence Carefully
- Self-reported diet, alcohol and smoking data may be inaccurate.
- Observational data may contain confounding variables, so an association does not prove that one lifestyle factor acted alone.
Self review
- State the BMI equation.
- Calculate waist-to-hip ratio from two measurements.
- How does alcohol damage the liver?
- Give two ways smoking raises cardiovascular risk.
