Cardiovascular Disease, Obesity, and Diabetes

Cardiovascular disease is a group of disorders of the heart and blood vessels, including coronary heart disease, stroke and high blood pressure; obesity is an excess of body fat that harms health, and diabetes mellitus is a disease in which blood glucose stays too high because of a lack of insulin or a reduced response to it. In brief: the three conditions share risk factors (poor diet, inactivity, smoking, age and genes) and often occur together. Body mass index (BMI = mass in kilograms ÷ height in meters squared) is a simple screening measure, and lifestyle changes can prevent a large part of cases.

Cardiovascular disease is the leading cause of death worldwide, and obesity and type 2 diabetes have risen in many countries in recent decades. This guide explains how atherosclerosis causes heart disease and stroke, what causes obesity and how it is assessed, how type 1 and type 2 diabetes differ, compares the conditions in a table, works through a BMI calculation and corrects common mistakes.

What is cardiovascular disease?

The main cause is atherosclerosis: the build-up of fatty deposits (plaques) in the walls of arteries. Damage to the lining of the artery, for example by high blood pressure, smoking or high levels of LDL cholesterol, lets lipids and white blood cells enter the wall, where an inflamed plaque grows. The artery narrows and becomes stiff.

• Coronary heart disease: the coronary arteries that supply the heart muscle are narrowed. This can cause chest pain on exertion (angina). If a blood clot (thrombus) blocks the artery, part of the heart muscle is deprived of oxygen and dies: this is a myocardial infarction (heart attack).
• Stroke: brain tissue is damaged because an artery is blocked by a clot (ischemic stroke, the most common type) or bursts (hemorrhagic stroke).
• Hypertension (high blood pressure): often has no symptoms, but strains the heart and damages arteries and kidneys. A reading is given as systolic over diastolic pressure in mmHg, and values persistently at or above about 130/80 to 140/90 are considered high, depending on the guideline.
• Heart failure: the heart cannot pump enough blood to meet the body’s needs.

Risk factors: smoking, a diet high in saturated fat, salt and processed foods, physical inactivity, obesity, diabetes, excessive alcohol, stress, increasing age, being male (before the menopause), and family history. Cholesterol is carried in the blood by lipoproteins: LDL (“bad”) deposits cholesterol in arteries, and HDL (“good”) carries it back to the liver. Treatments include drugs such as statins (which lower cholesterol), antihypertensives and anticoagulants, and procedures like angioplasty with stents and bypass surgery.

What is obesity?

Obesity is excess body fat that increases the risk to health. It develops when energy intake exceeds energy expenditure over a long time, and the surplus is stored as fat. The causes are complex: diet rich in energy-dense food and sugary drinks, low physical activity, genetic susceptibility (variants of genes such as FTO), hormones, sleep, some medicines, and the social and food environment.

In adults, the WHO classifies BMI as:

• below 18.5: underweight;
• 18.5 to 24.9: healthy weight;
• 25.0 to 29.9: overweight;
• 30.0 and above: obese.

BMI does not distinguish muscle from fat or show where the fat is. A muscular athlete may have a high BMI without excess fat. Fat around the abdomen (visceral fat) is more harmful than fat under the skin, so waist circumference and waist-to-hip ratio are also used. Obesity raises the risk of type 2 diabetes, hypertension, coronary heart disease, stroke, some cancers, sleep apnea and arthritis.

What is diabetes?

Blood glucose is regulated by the hormones insulin (from beta cells in the pancreas, lowers glucose by promoting uptake in cells and storage as glycogen) and glucagon (from alpha cells, raises glucose). In diabetes mellitus, this control fails, and the glucose level in the blood remains high (hyperglycemia). Symptoms include frequent urination, thirst, tiredness, weight loss and slow healing. Long-term high glucose damages blood vessels and nerves, causing heart disease, kidney failure, blindness (retinopathy), nerve damage and amputations.

• Type 1: an autoimmune disease in which the immune system destroys the beta cells, so the body makes little or no insulin. It usually starts in childhood or young adulthood, and requires insulin injections or a pump.
• Type 2: the cells respond poorly to insulin (insulin resistance), and the pancreas eventually cannot make enough. It is most common (about 90 percent of cases), is linked with obesity, inactivity, age and genes, and can often be managed or delayed with diet, exercise and weight loss, and drugs such as metformin.
• Gestational diabetes: high glucose that appears in pregnancy and usually resolves after birth, but raises later risk of type 2 diabetes.

Diagnosis uses a fasting blood glucose test, a glucose tolerance test or the HbA1c test, which reflects the average glucose over about 2 to 3 months.

The three conditions compared

How can these diseases be prevented?

• Do not smoke, and avoid exposure to smoke.
• Eat a diet rich in vegetables, fruit, whole grains and fish, and low in salt, sugar and saturated fat.
• Be physically active: the WHO recommends at least 150 minutes of moderate activity per week for adults.
• Keep a healthy weight, and limit alcohol.
• Check blood pressure, cholesterol and glucose regularly, particularly with a family history.
• At the level of the population: food labeling, taxes on sugary drinks, tobacco control and safe places for exercise.

Worked example: calculating BMI

A woman has a mass of 80 kg and a height of 1.75 m. Another adult has a mass of 95 kg and a height of 1.80 m.

1. Formula: BMI = mass (kg) ÷ height² (m²).
2. First person: height² = 1.75 × 1.75 = 3.0625. BMI = 80 ÷ 3.0625 = 26.1 kg/m².
3. Category: 26.1 is between 25.0 and 29.9, so this is overweight.
4. Second person: height² = 1.80 × 1.80 = 3.24. BMI = 95 ÷ 3.24 = 29.3 kg/m², which is also in the overweight range, close to the obese threshold.
5. Mass for BMI 24.9 (second person): 24.9 × 3.24 = 80.7 kg, so a loss of about 14 kg would take this person to the top of the healthy range.

BMI is a screening tool. A doctor would also consider the waist circumference, blood pressure, blood glucose, cholesterol and family history.

How were these diseases understood?

Ancient physicians described the sweet urine of diabetes; the name “mellitus” refers to honey. Frederick Banting and Charles Best, working with J. J. R. Macleod and James Collip, isolated insulin in 1921 to 1922, and the first patients were treated, which turned type 1 diabetes from a fatal disease into a manageable one. Frederick Sanger determined the amino acid sequence of insulin in 1955. The Framingham Heart Study, begun in 1948, introduced the term “risk factor”. Statins were developed in the 1970s and 1980s, based on work by Akira Endo and by Brown and Goldstein on LDL receptors.

Which mistakes are common?

Mistake 1: Confusing heart attack and cardiac arrest

A heart attack is a blockage of blood supply to the heart muscle. Cardiac arrest is when the heart stops pumping effectively, often because of an electrical fault. A heart attack can lead to cardiac arrest.

Mistake 2: Thinking that type 2 diabetes is caused only by eating sugar

It results from insulin resistance, with obesity, inactivity, age and genes all involved. Type 1 diabetes is not caused by diet.

Mistake 3: Treating BMI as a perfect measure

It does not distinguish muscle from fat, and the thresholds can differ among populations.

Mistake 4: Confusing insulin and glucagon

Insulin lowers blood glucose, and glucagon raises it.