It is estimated that coronary heart disease (CHD) affects approximately 2.3 million people in the UK alone.¹ It is responsible for a mortality rate of around 25% under 75 and is the leading cause of death in the UK.² Therefore, recognising CHD and ensuring adequate treatment to prevent further mortality and health complications is a significant health issue.

The purpose of this article is to explore and understand the link between CHD and cholesterol, and how CHD is diagnosed, managed and prevented. As well as examining new evidence questioning this link.

What is CHD?

Coronary heart disease (CHD), also known as coronary artery disease (CAD), is when blood flow to the heart is reduced or stopped. This is largely due to the buildup of fatty deposits and plaque in the coronary arteries which narrows the space within the arteries thereby reducing the blood flow and overall circulation.³

What is cholesterol?

Cholesterol is a waxy, fatty substance composed of carbon, oxygen and hydrogen that is involved in important bodily functions. This includes forming cell membrane structures and keeping them mobile, producing steroid hormones to control inflammation, immune response and metabolism, regulating salt/water balance and developing sexual characteristics. 

Cholesterol also produces vitamin D which is needed for bone development and calcium absorption, and it forms bile salts for fat digestion in the liver. The liver generates most of the body’s cholesterol. The rest comes from the food we eat. As cholesterol is fat-rich, it is not able to be dissolved in water and is therefore transported in the blood via specialised proteins called lipoproteins.⁴

High-density lipoprotein (HDL)

Termed as “good cholesterol”, HDL absorbs excess cholesterol by carrying it back to the liver for removal. Foods that increase HDL levels in the body include fish, high in omega-3 fatty acids, and oils high in monounsaturated fats such as olive and avocado oil and whole grains.

Low-density lipoprotein (LDL)

Termed as “bad cholesterol”, LDL can build up in the walls of arteries, causing arterial passages to narrow, reducing the flow of oxygen-rich blood through the body as well as causing a blockage leading to further complications. Foods that increase LDL levels include those high in saturated fat such as red meat and animal fats such as butter, lard and hard cheeses.

Other lipoproteins

Very low-density lipoprotein (VLDL), another “bad” cholesterol, also can contribute to the buildup of plaque in arteries. In addition to intermediate density lipoprotein (IDL).

Triglycerides

In addition to lipoproteins, there are triglycerides, a fat which helps to provide the body energy. High triglycerides may lead to hardening of the arteries and also contribute to CHD leading to heart attacks or strokes.^4,5

Fig1: Types of lipoproteins¹⁷

Risk factors for high cholesterol

• Unhealthy diet
• Sedentary lifestyle with limited exercise
• Smoking
• Obesity
• Family history of high cholesterol (familial hyperlipidemia)

Atherosclerosis: how does high cholesterol cause CHD?

Figure 2: Atherosclerosis progression¹⁸

Atherosclerosis is the thickening or hardening of the arteries due to plaque buildup in the inner arterial lining. This occurs in stages over many years and cholesterol plays a large role in this.

Endothelial damage

The first stage is damage to the endothelial lining (smooth lining) of the arteries, this then stimulates an immune response where macrophages (white blood cells) travel to the injury site causing inflammation within the artery and its wall.

Fatty streak

This surface is further damaged by fatty streak formation. A yellow streak of cholesterol accumulates at the endothelial site damage, the foam cell macrophages engulf cholesterol to remove it. The more foam cells accumulate the further endothelial damage.

Plaque formation

Dead foam cells and other substances add onto the fatty streak causing a plaque to form. A fibrous cap of smooth muscle cells forms over the plaque, stabilising this. The plaque grows, narrowing the width of the artery and reducing blood flow and oxygen to the body’s tissues and organs.

Plaque rupture and erosion

The plaque can then burst and the fibrous cap that covers the plaque can break through. Or the fibrous cap is intact and the plaque itself erodes. In both cases, this leads to the formation of a clot which obstructs blood flow and oxygen causing CHD.^6,7

Symptoms of CHD 

• Chest pain (angina), sudden pain in the centre of the chest due to reduced blood flow to the heart, this can radiate to the left side of the jaw neck, shoulder and arm.
• Breathlessness
• Nausea
• Lightheadedness or dizziness

However, some people may not have any symptoms before being diagnosed with CHD, therefore other tests are conducted if CHD is suspected.³

Complications of CHD

• Myocardial infarction: a heart attack due to sudden blockage of blood flow to the heart
• Arrhythmia: an irregular heartbeat, because of a lack of oxygen to different regions of the heart, the heart cannot beat as normal
• Heart failure: the inability of the heart to pump blood properly around the body
• Ischaemic stroke: a blood clot can break from its site of formation in the coronary artery and travel and block an artery near the brain. This results in a lack of oxygen leading to brain tissue death and a possible major bleed in the brain⁸

All these issues have a significant risk of mortality and disability leading to a reduced quality of life.

Diagnosing high cholesterol and CHD

Cholesterol: High cholesterol levels are diagnosed via a lipid profile blood test which gives a breakdown of the types of cholesterol in the blood. The NHS advises LDL cholesterol to be lower than 2 mmol/L, and total cholesterol to be less than 5 mmol/L. HDL level is to be higher than 1 mmol/L.⁹

CHD: CHD is diagnosed via a risk assessment by a general practitioner (GP) to assess the person's risk for a potential heart attack or stroke alongside a medical history, blood pressure and cholesterol check which is done usually after a 12-hour fast so as not to affect results. As well as further tests including, an ECG, exercise stress tests, X-rays, MRIs, CT scans, coronary angiography and an echocardiogram.³

Treatment and management of CHD

The recommended treatment for CHD is decided by a cardiologist (heart specialist) based on a person's CHD severity. Where CHD is not potentially life-threatening, generally drug management suffices. This includes calcium channel blockers, beta blockers and ACE inhibitors which all work differently to reduce blood pressure and prevent damage to the arterial walls. 

Aspirin helps to reduce the thickness and stickiness of blood allowing for better blood flow through arteries that may be obstructed due to plaque formation, it also prevents blood clot formation. Statins help to lower cholesterol by absorbing free cholesterol in the bloodstream and returning this to the liver for destruction.³

In more severe cases where the coronary arteries have become severely occluded, surgery may be the best option. This includes coronary artery bypass surgery (CABG) where a healthy blood vessel is taken from the chest, arm, or leg and attached to the coronary artery above and below the arterial blockage. As well as stent placement and angioplasty which helps to mechanically squash the existing plaque with a balloon catheter (tube) and widen the artery to aid blood flow.¹¹

Preventing CHD and high cholesterol

As the saying goes, prevention is better than cure. Due to the significant detrimental effects of CHD and high cholesterol, cholesterol levels should remain in the healthy range, so that CHD can be prevented. This is done by regularly checking cholesterol levels via blood tests every 3-6 months, to ensure stable levels. A balanced diet with plenty of fruit and vegetables, whole grains, and healthy fats ensures that LDL levels remain low and HDL levels are elevated.

As well as maintaining a healthy weight and body mass index (BMI) with regular exercise for around 30 minutes a day, and quitting smoking. If patients suffer from other health problems such as diabetes and hypertension, it is important they are also careful so as not to increase the risk of developing CHD.³

What does research say?

The link between cholesterol and heart disease gained attention due to the Ancel Keys Seven Countries Study.¹² This showed that countries with the highest intake of saturated fat and cholesterol had the highest rates of heart disease. Thus, this finding has become the medical consensus and informs recommendations in medical guidelines worldwide. More recent studies have also found a correlation between cholesterol and CHD.^13-14

However, there is some conflicting evidence, a 2019 study conducted by the American Heart Association found that dietary cholesterol may not be contributing as strongly to CHD as it seems.¹⁵ In the same year, another study showed that consumption of red meat high in saturated fat and cholesterol found a lower heart disease risk. However, this study was only able to show association, not causation. Very few independent randomised controlled studies have been conducted on cholesterol and CHD.¹⁶ Therefore, further studies are needed to examine this further.

Summary

CHD remains a significant health risk and cause of early mortality. A contributing factor is high cholesterol where the higher the cholesterol levels, the higher the CHD risk which aids in the formation of plaque thereby worsening CHD outcomes. Therefore, adhering to a healthy lifestyle helps to prevent this. There is newer evidence to suggest that the relationship between cholesterol and CHD may not be so clear-cut. However, further studies are required to establish this theory.