AN ANALYSIS OF THE ASSOCIATION BETWEEN BODY MASS INDEX AND BLOOD PRESSURE AMONG ADULTS ATTENDING THE GENERAL OUTPATIENT CLINIC OF FEDERAL MEDICAL CENTRE ASABA

CHAPTER ONE

INTRODUCTION

General Consideration of Obesity Obesity is one of the most common disorders in medical practice.

Obesity which constituted a significant public health problem in the developed world

has become increasingly more prevalent in many African countries 3,.4 Also, it has become an increasingly important medical problem in children and adolescents

as the prevalence of obesity is also increasing rapidly in young people in several developing nations worldwide.

Some progress has been made in understanding of its causes, prevention, treatment and implications for health. Definition of Obesity Obesity is defined as an excess of adipose tissue.

Measurement of Obesity Physical examination may be sufficient to detect excess body fat. However more quantitative evaluation is performed by calculating the BMI. The BMI closely correlates with excess adipose tissue and estimates the total body ebcid:com.britannica.oec2.identifier.IndexEntryContentIdentifier?idxStructId=202365&library= EBfat. It is calculated by dividing measured body weight in kilograms by the height in metres squared (weight/ height).

BMI may also be defined as a mathematical ratio of height to weight

that can be linked with body fat percentage and with indices of health risk.

Clinically, BMI determines whether an individual is obese or not. Several classifications and definitions exist for degrees of obesity; the most widely accepted being the World Health Organization (WHO) criteria, based on BMI.

According to the current WHO BMI classifications for adults, the following are the categories of BMI: <18.5 kg/m

(class III obesity).

According to Uwaifo and Arioglu, BMI is far more commonly used to define obesity and has been found to closely correlate with the degree of body fat in most settings.

Other measures of body fat such as waist circumference or waist-to-hip ratio are regarded as better estimates of abdominal adiposity. Factors other than total weight, however, are also important. For instance upper body obesity is a greater health hazard than lower body obesity. Obese patients with increased abdominal circumference (> 102 cm in men and 88 cm in women) or with high waist–hip ratios (> 1.0 in men and > 0.85 in women) have a greater risk of diabetes mellitus, stroke, coronary artery disease than equally obese patients with lower ratios. 7, 8 Furthermore, visceral fat within the abdominal cavity is more hazardous to health than subcutaneous fat around the abdomen.

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More accurate quantification of body fat requires sophisticated techniques not usually available in clinical practice including anthropometry, densitometry, computed tomography, magnetic resonance imaging, and electrical impedance. Health Consequences of Obesity A great number of disorders occur with greater frequency in obese people.

The most common of these are hypertension, type 2 diabetes mellitus, hyperlipidaemia, coronary artery

disease, degenerative joint disease, psychosocial disability and metabolic syndrome. 10,

11,

Obesity which is often perceived as a cosmetic problem in individuals, is associated with cancers of the colon, ovary and breast. Gallbladder diseases are also more prevalent in the obese.

Surgical and obstetric risks are greater.

Obese patients also have a greater risk of sleep apnea.

Several studies have documented that obese individuals are also subject to various forms of social discrimination, major depression and binge eating disorder.

Aetiology of Obesity Obesity can result from increased energy intake, decreased energy expenditure, or a combination of the two.

It is also considered to be the direct result of a sedentary lifestyle plus chronic ingestion of excess calories.

Although these factors are the principal causes in many cases, there is evidence for strong genetic influences on the development of obesity. These genetic effects appear to relate to both energy intake and expenditure. Single-gene mutations cause both hyperphagia and diminished energy expenditure.

Most human obesity develop from the interactions of multiple genes, environmental factors, and behaviour. Less than 1% of obese patients have an identifiable secondary cause of obesity such hypothyroidism and Cushing syndrome.

Medical Evaluation of an Obese Patient Historical information should be obtained about age at onset, recent weight changes, family history of obesity, occupational history, eating and exercise behaviour, cigarette and alcohol use, and psychosocial factors including assessment for depression and eating disorders. Physical examination should assess the degree and distribution of body fat, overall nutritional status, and

signs of secondary causes of obesity. All obese patients should be assessed for medical consequences of their obesity by screening for the metabolic syndrome, blood pressure, waist circumference, fasting plasma glucose, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and triglycerides. Treatment of Obesity Successful treatment of obesity involves a multidisciplinary approach to weight loss with hypocaloric diets, behaviour modification, aerobic exercise, and social support.

Emphasis must be on intake of a wide variety of predominantly "unprocessed" foods. Foods that provide large amounts of calories including fat, sucrose, and alcohol are limited and maintenance of weight loss encouraged.

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Patients are commonly maintained on such programmes for 4–6 months with loss of an average of approximately 15% of initial weight.

Long-term weight maintenance requires concurrent behaviour modification, long-term use of low-calorie diets, careful self-monitoring, and regular exercise.

Social support is essential for a successful weight loss programme. Continued close contact with clinicians and involvement of the family and peer group are useful techniques for reinforcing behavioural change, preventing social isolation and success of treatment.

Exercise offers a number of advantages to patients trying to lose weight.

Aerobic exercise directly increases the daily energy expenditure and is particularly useful for long-term weight maintenance.

Exercise plus diet results in greater weight loss than diet alone.

Medications for the treatment of obesity are available both over the counter and by prescription. Obesity drugs may be used as part of a comprehensive weight loss programmes for patients with BMI > 30 or those with BMI > 27 with obesity-related risk factors.

Phentermine, diethylpropion, mazindol are approved for short-term use only. Two additional medications

approved for weight loss include sibutramine and orlistat.

Sibutramine, typically at doses of 10 mg/d orally, results in average weight losses of 3–5 kg more than placebo in studies extending over 6–12 months. Side effects include dry mouth, anorexia, constipation, insomnia, and dizziness. In some patients, sibutramine may substantially increase blood pressure.

In randomized trials with up to 2 years of follow-up, orlistat has resulted in 2–4 kg greater weight loss than placebo.

The recommended dose of orlistat is 120 mg orally three times daily with meals. Orlistat may result in diarrhoea, gas, and cramping and perhaps also reduced absorption of fat-soluble vitamins.

Another class of medications under investigation is selective cannabinoid-1 receptor antagonists.

In a year-long studies of one cannabinoid-1 receptor antagonist, rimonabant, a 20- mg dose resulted in 5 kg greater weight loss than placebo.

Bariatric surgery is an increasingly prevalent treatment option for patients with severe

Most popular is the Roux-en-Y gastric bypass (RYGB).

In most centres, the operation can be done laparoscopically. RYGB typically results in substantial amounts of weight loss— close to 50% of initial body weight in some studies. Complications occur in up to 40% of persons undergoing RYGB surgery

and include peritonitis due to anastomotic leak, abdominal wall hernias, staple line disruption, gallstones, neuropathy, wound infections and thromboembolic disease. Gastric banding (GB) surgeries are increasing as an alternative procedure.

GB results in less dramatic weight loss than RYGB but with fewer short-term complications.

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Longer-term follow-up suggests that both procedures are associated with significant regaining of weight.

National Institute of Health consensus panel recommendations are to limit obesity surgery to patients with BMIs over 40 or over 35 if obesity-related comorbidities are present. The procedure is cost-effective for patients with severe obesity.

General Consideration of Hypertension Blood pressure is an important indicator of the health of the circulatory system. A number of conditions have the potential to elevate blood pressure. For instance, obesity is associated with elevated blood pressure both in adults and children. 11, 39 Sixty-six million Americans have elevated blood pressure (systolic blood pressure 140 mm Hg or diastolic blood pressure 90 mm Hg).

Of these, 72% are aware of their diagnosis, but only 61% are receiving treatment and only 35% are under control using a threshold criterion of 140/90 mmHg.

The prevalence of hypertension increases with age and is more common in blacks than in whites. 39, 40

Measurement of Blood Pressure Blood pressure is measured with a well-calibrated sphygmomanometer. The bladder width within the cuff should encircle at least 80% of the arm circumference. Readings are taken after the patient has been resting comfortably, back supported in the sitting or supine position, for at least 5 minutes and at least 30 minutes after smoking or coffee ingestion.

Classification of Hypertension Primary (Essential) Hypertension Primary (essential) hypertension is the term applied to the 95% of hypertensive patients in which no single cause can be identified. In this group, hypertension results from complex interactions between multiple genetic and environmental factors.

Secondary Hypertension

Approximately 5% of patients with hypertension have identifiable specific causes.

Causes of secondary hypertension include sleep apnea, drug-induced, chronic kidney disease, primary aldosteronism, renovascular disease, long-term corticosteroid therapy, Cushing syndrome, phaeochromocytoma, coarctation of the aorta, thyroid, parathyroid disease.

Complications of Hypertension Complications of hypertension are related to sustained elevations of blood pressure, with consequent structural and functional changes in the vasculature and heart.

They include: Hypertensive Cardiovascular Disease: left ventricular hypertrophy is associated with congestive heart failure, ventricular arrhythmias, myocardial ischaemia

Hypertensive Cerebrovascular Disease and Dementia: hypertension is the major predisposing cause of haemorrhagic and ischaemic stroke. Preceding hypertension is associated with a higher incidence of subsequent dementia of both vascular and Alzheimer types

. Hypertensive Kidney Disease: chronic hypertension leads to nephrosclerosis, a common cause of kidney disease that is particularly prevalent in blacks

. Aortic Dissection: hypertension is a contributing factor in many patients with dissection of the aorta. 42,43 Clinical Features of Hypertension Mild to moderate primary hypertension is largely asymptomatic for many years.

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The clinical and laboratory findings are mainly referable to involvement of the target organs:

heart, brain, kidneys, eyes, and peripheral arteries.

Recommended tests includes the following: haemoglobin, urinalysis detects haematuria, proteinuria, and casts, signifying kidney disease, renal function tests shows creatinine level, fasting blood sugar level excludes diabetes, plasma lipids indicate atherosclerosis risk, elevated serum uric acid contraindicates diuretic therapy, serum electrolytes shows sodium and potassium levels.

Electrocardiography may reveal left ventricular hypertrophy, chest X-ray and echocardiography may be indicated in the evaluation of the patients with clinical symptoms or signs of cardiac disease . Additional diagnostic studies are indicated only if the clinical presentation or routine tests suggest secondary or complicated hypertension.

These may include tests such as 24-hour urine free cortisol, plasma metanephrines and the plasma aldosterone/renin ratio for detection of endocrine causes. Renal ultrasound may show polycystic kidneys. Further evaluation may include CT scan and MRI to show coarctation of aorta or renal arteriography.

Treatment of Hypertension Approaches to treatment of hypertension involve lifestyle modifications including weight reduction, reduced alcohol consumption and reduced salt intake.

Gradually increasing activity levels should be encouraged. Calcium and potassium supplements have been advocated.

Smoking cessation reduces overall cardiovascular risk. Drug Therapy in Hypertension There are now many classes of antihypertensive drugs. Diuretics, Beta-blockers, Renin inhibitors, ACE inhibitors, Calcium channel blockers, and ARBs are suitable for initial therapy based on efficacy and tolerability.

Obesity-Related Hypertension Obesity increases the risk of the development of hypertension. A strong association between blood pressure and body mass index has been observed in the developed and developing countries.

This linkage has been the subject of several recent reviews.

Obesity-associated hypertension is characterized by activation of the sympathetic nervous system, activation of the renin-angiotensin system, and increased sodium retention.

Obesity is associated with increased blood flow, vasodilatation, cardiac output, renal sodium retention leading to hypertension.

In obese individuals, there is obesity-related alteration in pressure-natriuresis relationship. Sustained hypertension occurs when the relationship between arterial pressure and natriuresis is abnormal (ie, when pressure-natriuresis is deranged).

Elaboration of leptin, a hormone produced in fat that produces satiety and weight loss by diminishing caloric intake and by activating the sympathetic nervous system to enhance thermogenesis, can cause hypertension.

Obesity is associated with hyperinsulinaemia. Because insulin can enhance tubular reabsorption of sodium, insulin also could help support an elevated arterial pressure.

Structural changes in the kidney secondary to obesity seem to be important. The pressure of fat deposits around the kidneys, coupled with increased abdominal pressure secondary to central obesity, has been suggested as an additional cause of disordered renal sodium Obesity and Hypertension Sequelae Hypertension is associated with well-known sequelae, including coronary artery disease, cerebrovascular disease, renal insufficiency, atherosclerosis, left ventricular hypertrophy, atrial fibrillation, and congestive heart failure. Obesity-related hypertension is no different in this regard in that it predisposes to these conditions as well.

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Hypertension leads to concentric hypertrophy. The obese individual with hypertension demonstrates eccentric left ventricular hypertrophy in

addition to concentric hypertrophy. 57, 58 Considerable evidence suggests that obesity-related hypertension is associated with an increased risk of renal insufficiency. The pathophysiologic mechanisms associated with the onset of obesity-related hypertension demonstrate that hyperfiltration, stimulation of the renin-angiotensin system, and obesity-related structural alterations in the kidney all set the stage for progressive renal disease.

Therapy for obesity-related hypertension Therapy for obesity-related hypertension for the most part follows the standard line of high blood pressure treatment but perhaps with a greater emphasis on diet. Lifestyle modifications and dietary changes, followed by pharmacotherapy, remain standard.

However, several principles may help to optimize the therapy of patients with obesity-related hypertension. First, the mainstay of therapy must be weight loss.

This must be a primary goal in the therapy of obesity-related hypertension. Weight loss will reverse many of the pathophysiologic mechanisms that sustain hypertension in obesity-related hypertension. 61, 62 It seems likely that interruption of the renin- angiotensin system , inhibition of sympathetic nervous activity, and diuresis should all be helpful in treating obesity-related hypertension. Diuretic therapy in an obese patient may worsen glucose tolerance or produce frank diabetes, thereby adding additional risk. Beta sympathetic blockade can be associated with worsening glucose tolerance, and alpha blockade may be associated with postural hypotension. However, interruption of the renin-angiotensin system in general does not worsen, and may improve glucose tolerance and is usually well tolerated.

However, interruption of the renin- angiotensin is not without risk. Angiotensin-converting enzyme inhibition can be associated with angioedema, and all drugs that interrupt the renin-angiotensin are toxic to the foetus and must be discontinued if pregnancy occurs. Newer agents in time may have a role. For instance, Peroxisome

proliferator–activated receptor gamma agonists improve insulin resistance and in some cases reduce arterial pressure.

Rimonabant, the cannabinoid receptor 1 receptor blocker lowered blood pressure in patients in weight loss trials. 63, 64,

Rationale for the Study Obesity has become one of the most urgent public health problems and poses a major threat to human health worldwide.

Obesity and hypertension are becoming increasingly more prevalent in many African and other developing countries with nutritional transition as a result of urbanisation and adoption of western lifestyles. 67, 68

Recently, as a result of economic growth and urbanisation in China, changes in lifestyle and diet have led to an increase in obesity as well as an increase in the burden of obesity-related chronic diseases.

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Despite a growing burden of obesity and hypertension in developing countries, there is limited information on the contribution of body mass index to blood pressure in these populations. In many cities including Asaba, fast food outlets are rapidly springing up with high patronage, leading to the consumption of energy-dense foods such as refined foods, snacks, creamy salad dressings, fatty meats, fried chicken. This has important implications for development of chronic non-communicable diseases such as obesity and hypertension in the people. In addition, there is sedentary lifestyle among the populace characterised by decreased physical activity with implications for the upsurge in chronic non-communicable diseases. Additionally, hypertension places an excessive financial burden on populations and health systems, consuming scarce resources. Presently, no data are available on the association between body mass index (BMI) and blood pressure in patients attending the General Outpatient Clinic of Federal Medical Centre, Asaba, Delta State. Therefore, this study intends to generate relevant information that helps to

clarify the patterns of the association between excess body weight and blood pressure values in the patients attending the General Outpatient Clinic of FMC Asaba with the following general and specific objectives: General Objective To investigate the relationship between body mass index and blood pressure in the patients attending the General Outpatient Clinic of Federal Medical Centre, Asaba, Delta State in order to create awareness for prevention, early detection and prompt management of hypertension. Specific Objectives 1) To identify the sociodemographic characteristics of the study participants attending the General Outpatient Clinic of Federal Medical Centre, Asaba, Delta State 2) To evaluate the association of the body mass index of the study participants with the systolic blood pressure 3) To evaluate the association of the body mass index of the study participants with the diastolic blood pressure

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