Obesity and heart diseaseSunday, January 09, 2022
Paul Edwards and Ernest Madu
OBESITY is an issue that has been increasingly prominent in both developed and developing economies worldwide. It is associated with the epidemic of chronic disease and more recently, its role in cardiac disease has been recognised.
An important finding over the past two decades has been that all fat is not created equal when it comes to risk of chronic disease. We can think of fat that is under the skin (subcutaneous fat), and fat that is present in the body cavities or surrounding organs (visceral fat). Visceral fat is hormonally and metabolically active, with accumulation being associated with a higher risk of chronic disease than subcutaneous fat. Unfortunately, accurate assessment of the amount of visceral fat is not possible from clinical examination alone, however it is known that increased abdominal or belly fat is a reasonable clinical marker for the presence of visceral fat in the abdominal cavity. The risk for fat around the buttocks is much less. It is possible to measure visceral fat precisely by using a CT scan or MRI, however this information has yet to be shown to be useful in regular clinical care.
As we have noted previously, the prevalence of obesity in Jamaica is high, with the 2015-2017 Jamaica Health and Lifestyle survey finding that one in two Jamaicans were overweight or obese. Females were disproportionately affected, with two thirds of Jamaican women being overweight or obese. Obesity has long been associated with hypertension, diabetes, dyslipidemia (abnormal level of cholesterol and other fats in the blood) and sleep apnoea. More recently, it's importance in cardiovascular disease is being recognised.
How do we diagnose obesity?
The most common method of diagnosis is the use of the body mass index or BMI. For this measurement, an individual's weight in kilograms is divided by the height in metres squared. For much of the western world, a BMI of less than 25 is considered normal. BMI's of 25-30 are considered overweight and BMI's of greater than 30 are considered to represent obesity. It has been recognised, however, that some ethnic groups have normal ranges that are different. For example, in Southeast Asia a BMI above 23 is considered overweight. Also, BMI has limitations in predicting chronic disease risk as it does not differentiate between different types of fat deposition. It can also be misleading in individuals whose increased weight is secondary to muscle mass. As noted above, there is a strong correlation between abdominal obesity and visceral fat deposition so that measures of abdominal obesity may improve clinical assessment when compared to the BMI alone. A simple measure of abdominal obesity is the waist circumference. Another commonly used measure is the waist to hip ratio, where the circumference of the waist and hip are compared. Studies have found that measures that include some measure of belly fat do a better job at predicting chronic disease risk in the obese.
How does obesity affect the risk for cardiovascular disease?
It has long been known that obesity is an important factor in the genesis of cardiac risk factors. For example, an obese person with normal blood pressure has a 70 per cent risk of developing hypertension over the next 10 years. Through it's effect on traditional cardiac risk factors such as hypertension, diabetes and dyslipidemia, obesity has an indirect effect on morbidity and mortality from cardiovascular disease. Of some interest is not only the visceral fat found in the abdominal cavity, but fat deposits around the heart. Fat deposits can accumulate both next to the heart muscle and within the fibrous sack that keeps the heart in place in the chest cavity. Increases in fat deposits around the heart have been associated with increasing obesity, particularly when that obesity is found in the abdomen. These fat deposits next to the heart have been shown to release chemicals into the bloodstream and are associated with increased stiffness of the arteries, elevated blood pressure and resistance to the action of insulin. Some studies are suggesting that these fat deposits can also independently predict risk and severity of cardiac disease.
Obesity and coronary artery disease
As noted above, obesity heightens the traditional risk factors that lead to the deposition of cholesterol in the arteries of the heart and more generally, atherosclerosis. In addition to this, obesity plays a more direct role through its effects on systemic inflammation. This inflammation is chronic and affects blood vessels throughout the body, promoting the atherosclerotic process. The effects of this inflammation act to start the deposition of cholesterol, increase the rate of cholesterol accumulation, and to reduce the ability of blood vessels to resist cholesterol deposition. Studies have suggested that these effects are particularly associated with abdominal fat. Other studies have found that increases in the thickness of blood vessels (an early marker of cholesterol deposition) are associated with obesity, with greater effects being seen in obesity that starts early in life and continues through adulthood.
Obesity and heart failure
Obesity is currently considered to be a strong risk factor for the development of heart failure. Increasing levels of obesity are associated with an increasing risk of heart failure. The risk appears to be greater for heart failure in which the heart pumps normally, but weakness of the pumping action of the heart can also occur. Obesity leads to hypertension and thickening of the heart muscle, both of which over time can lead to heart failure. But, as with coronary artery disease, there are direct mechanisms by which obesity can affect heart function. Obesity, particularly visceral obesity, is associated with enlargement of heart muscle cells, scarring within heart muscle, and inflammation within heart muscle. All of this, over time, can lead to deterioration in cardiac function. Studies of patients who are overweight and obese have suggested an increase in the risk of heart failure of 36 per cent and 56 per cent, respectively.
Obesity and arrhythmias/sudden death
Obesity has been associated with many abnormalities of cardiac rhythm. It is a strong risk factor for the most common sustained arrhythmia - atrial fibrillation. This increased risk is likely mediated through its effects of increasing the size of the atria's and scarring of the atrial tissue. Successful weight loss, particularly after bariatric surgery, has been shown to reduce the risk of recurrence of atrial fibrillation. Aside from atrial fibrillation, obesity is associated with other serious rhythm disorders including ventricular fibrillation and ventricular tachycardia. Of most concern is the association of obesity with the risk of sudden cardiac death. Studies have suggested that for each five-unit increase in the BMI, the risk of sudden cardiac death increases by 16 per cent. A study in Finland found that after coronary artery disease, obesity is the next most frequent cause of sudden death – being 23 per cent of cases in their study.
What can I do to lower my risk of obesity and it's complications?
For most of us, the best advice is to avoid becoming overweight. This ideally starts in childhood with the development of habits that we will carry throughout life. We should choose diets that minimise processed food but maximise foods of low caloric density, including fruits, vegetables and low-glycemic carbohydrates. It is important to limit “empty calories”, including alcohol and sodas. We should make a habit of weighing ourselves regularly and making exercise part of our lifestyle. These are important lessons to take to heart at this time of the year when eating and drinking are part of the holiday celebrations. We hope that you enjoy the season in moderation and wish you and your families a healthy new year.
Dr Ernest Madu, MD, FACC and Dr Paul Edwards, MD, FACC are consultant cardiologists for Heart Institute of the Caribbean (HIC) and HIC Heart Hospital. HIC is the regional centre of excellence for cardiovascular care in the English-speaking Caribbean and has pioneered a transformation in the way cardiovascular care is delivered in the region. HIC Heart Hospital is registered by the Ministry of Health and Wellness and is the only heart hospital in Jamaica. Correspondence to firstname.lastname@example.org or call 876-906-2107