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Diabetes Mellitus, Obesity & the Heart

Published in The Business Times on 8th March 2019

By Senior Consultant Cardiologist, Dr Wong Siong Sung

Diabetes mellitus and obesity are closely linked to the increase of the prevalence of cardiovascular disease. Based on Singapore Myocardial Infarction Registry annual report 2016, more than half of the patients admitted with myocardial infarction (heart muscle damage due to heart attack) were found to have cardiovascular risk factors of diabetes mellitus (50.2%) and obesity (59.4%). It is prudent that we are aware of this and take necessary steps to prevent from getting diabetes mellitus, obesity and its complications.

Diabetes Mellitus

There are myths about diabetes mellitus. The myths include diabetes mellitus is caused by eating excessive amount of sweet food and it is simply a mere presence of sugar in the urine. The truth is that diabetes mellitus is not necessarily just caused by eating too much sweet food although this may contribute ultimately to the development of diabetes mellitus. In addition, the presence of sugar in the urine is not required for the diagnosis of diabetes mellitus although many patients with diabetes mellitus have the presence of sugar in the urine. So, what is diabetes mellitus? Why is it important to know its implications to our health?

Diabetes mellitus basically is a chronic disease manifested by elevated blood glucose (sugar in layman’s terms) due to the inability of the body (pancreas) to produce insulin and respond to it effectively. Insulin is a hormone secreted by pancreatic beta cells to enable us to use the sugar from carbohydrates for energy and also to store the sugar for future use. Type 1 diabetes is characterized by autoimmune or nonautoimmune destruction of the pancreatic beta cells, leading to absolute insulin deficiency. It occurs in genetically susceptible persons and probably triggered by one or more environmental agents. Type 2 diabetes is much more common and is characterized by hyperglycaemia and variable degrees of insulin deficiency and resistance. Its occurrence most likely involves complex interplay among many genes and environmental factors. Importantly, excessive food intake for a prolonged period of time coupled with lack of physical activity will eventually cause overweight and obesity. Obesity induces insulin resistance. Consequently, hyperglycaemia (elevated blood glucose) develops. Hyperglycemia will further cause impaired pancreatic beta cell function and also exacerbate insulin resistance. As a result, diabetes mellitus develops.

 

American Diabetes Association criteria for the diagnosis of diabetes mellitus include the following:

  • Fasting plasma glucose ≥126 mg/dL (7.0 mmol/L) (Fasting is defined as no caloric intake for at least eight hours) or

  • Haemoglobin A1C ≥6.5 percent or

  • Plasma glucose level is ≥200 mg/dL (11.1 mmol/L) where the blood is tested 2 hours after consumption of 75-gram anhydrous glucose dissolved in water (Oral glucose tolerance test, OGTT) or

  • Random plasma glucose ≥200 mg/dL (11.1 mmol/L) in the presence of symptoms

In the absence of unequivocal hyperglycaemia, repeat blood testing will confirm the diagnosis.

Normal fasting plasma glucose is defined as <100 mg/dL (5.6 mmol/L).

Increased risk for diabetes (also referred to as "prediabetes") is defined by the presence of the following criteria:

  • Plasma glucose level falls between 140 and 199 mg/dL (7.8 to 11.0 mmol/L) where the blood is tested 2 hours after consumption of 75-gram anhydrous glucose dissolved in water (OGTT). This condition is also called impaired glucose tolerance (IGT).

  • Fasting plasma glucose is between 100 to 125 mg/dL (5.6 to 6.9 mmol/L). This is also referred to as impaired fasting glucose (IFG).

  • Hemoglobin A1C of 5.7 to 6.4 percent.

Based on National Health Survey 2010, Ministry of Health Singapore, the crude prevalence of diabetes among Singapore residents aged 18 to 69 years is 11.3%. One third of the diabetics were unaware that they had diabetes mellitus. Besides, the prevalence of impaired glucose tolerance among Singapore residents was in the range of 12 and 15% over the decade. Peoples who are found to have impaired glucose tolerance, one third of them are projected to develop diabetes in eight years.

Studies also showed that patients with type 2 diabetes mellitus also had high rate of asymptomatic coronary heart disease. Diabetics may have a blunted appreciation of ischemic pain, which result in atypical anginal symptoms, silent myocardial ischemia (lack of oxygen supply to heart muscle), or even silent myocardial infarction (heart muscle damage due to heart attack).

Type 2 diabetes mellitus was considered as coronary heart disease equivalent based on the observation that the seven-year incidence rates of myocardial infarction among patients with type 2 diabetes without prior myocardial infarction had the similar risk for myocardial infarction (20 and 19 percent, respectively) and coronary mortality (15 versus 16 percent) as patients without diabetes who had a prior myocardial infarction.

Obesity

The National Health Survey 2010 showed that 1 in 9 Singaporeans aged 18 to 69 is obese; a 57% increase from 2004 and 1.7 million Singaporeans with a Body Mass Index (BMI) of 23 or greater are susceptible to cardiovascular disease and diabetes. In addition, one million Singaporeans with BMI 23 or greater had either pre-diabetic or at least one or more chronic condition including diabetes. According to World Health Organization (WHO) definition, a BMI of 25-29.9kg/m2 is considered as overweight and BMI of 30kg/m2 or greater is obesity. However, based on body fat equivalence, the recommended BMI cut-off points for public health action in Asians were 23 kg/m2 in view of the risks as mentioned. BMI can be calculated using this formula: Body weight in kilograms divided by the square of the height in metres (kg/m2).

For example, if your body weight is 78kg and your height is 1.60 metre, your BMI is 30.5 (Obese).

BMI =78kg x (1.60x1.60) metre = 30.5

Obesity and overweight occurs as a person consumed more than what the body utilized for substantial period of time. This is contributed by lack of exercise, sedentary lifestyle and urbanization.

Harmful effects of obesity include the followings:

- More than 80% of type 2 diabetes is attributed to obesity.

-Obese individuals tend to develop high blood pressure.

- High level of total cholesterol, LDL cholesterol (bad cholesterol), triglycerides, and a reduction in HDL cholesterol (good cholesterol).

-Left ventricular hypertrophy (thickening of the heart muscle) develops as obesity is associated with volume overload, increased filling pressure to the heart and hypertension. Left ventricular hypertrophy is undesirable as it was associated with heart failure, ventricular arrhythmias, death following myocardial infarction and sudden cardiac death.

-Obese persons are more likely to develop atrial fibrillation (a form of irregular heart rhythm). Atrial fibrillation is known to increase the risk of stroke.

-Increased rate of death from all causes and from cardiovascular disease was observed in individuals with greater BMI with progressively greater mortality as BMI increases >25 kg/m2. 

-Excessive lipid accumulation in the heart muscle (myocardial steatosis) is thought to be one of the potential mechanisms of heart disease in obesity.  

-Obstructive sleep apnoea (OSA) is associated with obesity. OSA occurs when the throat muscles intermittently relax and block the airway during sleep. If left untreated, individuals with severe OSA have a two- to threefold increased risk of all-cause mortality compared with those without OSA. 

The Heart

In view of the significant risk of heart disease posed by diabetes mellitus and obesity, what tests can be done to evaluate our heart? A basic test such as electrocardiogram (ECG) can be done to assess the electrical activity of the heart. However, a normal ECG does not exclude coronary heart disease. If only two tests that were allowed to be performed apart from ECG in order to exclude coronary heart disease confidently and provide the most comprehensive evaluation of the heart in a non-invasive way, then CT coronary angiogram and echocardiogram are the tests of choice. CT coronary angiogram is a highly accurate imaging technique used to assess the presence of coronary artery narrowing (stenosis) from no narrowing (0%) to complete occlusion (100%). CT coronary angiogram has very high negative predictive value of 99%, meaning it is very reliable for ruling out significant coronary artery disease.

 

United Kingdom NICE guideline recommends CT coronary angiogram as the first line investigation for patients presenting with new onset chest pain due to suspected coronary heart disease in view of its high diagnostic accuracy and cost effectiveness. Even if minor coronary artery disease (defined as <50% narrowing) is detected, patients are often motivated to control their cardiovascular risk factors more aggressively. Severe coronary artery narrowing should be further managed and treated accordingly. Whereas echocardiogram is an ultrasound technique used to assess the heart function, valves and heart muscle thickness. Heart failure can be diagnosed using echocardiogram. Of course there are other alternative tests can be performed depending on the clinical scenario of a patient. 

For individuals without severe coronary heart disease, regular exercise is advised. Clinical Practice Guidelines 2016 by Health Promotion Board, Ministry of Health Singapore has recommended ≥150 minutes of moderate-intensity physical activity per week for overweight and obese adults in order to maintain health and prevent diseases. For weight loss, 150–420 minutes of moderate intensity physical activity per week is required. To maintain weight loss, adults should engage in 200–300 minutes of moderate-intensity physical activity per week. Long term adherence to reduced-calorie diets and close monitoring of body weight are also important. Diabetics and obese individuals should not hesitate to seek Cardiologist’s help for proper evaluation of their heart.

Dr Wong Siong Sung

Senior Consultant Cardiologist

Medical Director of Healthy Heart Specialist Centre

Medical Director of Somerset Imaging Centre

MD, FAHA, FRCP (Edinburgh), FASNC, FAMS (Cardiology)

MRCP (UK), MRCPS (Glasgow), DCBCCT (USA), DCBNC (USA)