If you have ever wondered what the link is between diabetes mellitus and coronary artery disease (narrowing of the heart arteries caused by cholesterol and fat deposit), the fact is that 75% of diabetic patients will die of cardiovascular disease^[1]. This is a staggering number that calls for the highest degree of vigilance and prevention.

There are currently 440,000 diabetic patients in Singapore, or 1 in 9 adults afflicted with the condition. It is estimated that by 2050, 1 in 5 adult Singaporeans will have diabetes mellitus^[2]. In addition, 12% of Singaporeans have prediabetes, and one third of them will progress to develop diabetes mellitus. Women with diabetes mellitus lose the natural protection against coronary artery disease (CAD) accorded by the female hormones, putting them at equal risk with males of the same age. The cost of national healthcare expenditure on diabetic care amounts to S$1 billion dollars, which has the potential to rise to S$2.5 billion by 2050^[3]. It is no wonder that the Singapore government declared a war on diabetes in 2016.

CAD is prevalent in diabetic patients. Based on an autopsy study^[4], approximately 50% of diabetic patients under the age of 65 years will have evidence of CAD. In those who are above 65 years, 75% will have established CAD. Diabetes mellitus increases the CAD risk in men by 2 times and women by 4 times^[5],[6]. It accelerates the rate of progression of the disease, causes higher rates of heart attack and heart failure, and a higher incidence of cardiac death compared with non-diabetic patients. The types of CAD in diabetes are also more complex, in that there are: more diffuse stenosis (narrowing), more calcified (hardened) disease, more complete occlusions (blockage) of the diseased blood vessels and multivessel involvement. Diabetic patients also fare worse after treatment with either coronary ballooning and stenting or coronary artery bypass operation compared with non-diabetics.   

The exact reasons for this worse CAD state are complex and multifactorial. It is said that persistent elevation of blood glucose changes the lipid profile of the patients, affects normal function of the inner lining of blood vessels(‘endothelial dysfunction’), and triggers more inflammation and increases the tendency to blood clot formation (‘thrombosis’) which causes the heart attack.

In addition, the symptom manifestations may differ between diabetic and non-diabetic patients. While chest pain is the common presenting symptom for a heart attack, diabetic patients may sometimes not experience any symptoms at all but encounter heart failure or sudden death. This is because diabetes mellitus affects the nerve conduction system and ‘masks’ the symptoms in these patients.

Prevention and treatment of diabetes mellitus to prevent heart disease is therefore of paramount importance. The Ministry of Health recommends that for all adults above 40 years of age, screening for diabetes mellitus should be performed in the form of fasting blood glucose tests. These may be carried out at an earlier age of 30 years should the person also have obesity, hypertension, family history of diabetes mellitus, gestational diabetes mellitus or existing coronary artery disease. The normal fasting blood glucose should be less than 6.1 mmol/L. Should the fasting blood glucose be between 6.1 to 6.9mmol/L, an oral glucose tolerance test should then be performed to confirm the diagnosis of diabetes mellitus. If a person’s fasting blood glucose is 7.0mmol/L or more, then he is considered to have diabetes mellitus^[7]. The treatment of diabetes mellitus should be multi-pronged and includes healthy lifestyle modification, regular monitoring of blood glucose levels, compliance with drug therapy and regular check-ups with doctors. By adopting these measures, it is possible to prevent and alter the natural course of the disease process and therefore prevent the dreaded complications of CAD in diabetic patients.

Prof Tan Huay Cheem is the Director of National University Heart Centre, Singapore (NUHCS); Senior Consultant Cardiologist at the National University Hospital, and Professor of Medicine with Yong Loo Lin School of Medicine, National University of Singapore. Prof Tan was the past President of Singapore Cardiac Society and presently a Board member/Honorary Secretary of the Singapore Heart Foundation.