Diabetes

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chapter 26 Diabetes

INTRODUCTION AND OVERVIEW

Diabetes mellitus is classified into several types:

• type 1 diabetes—constitutes about 5–10% of cases of diabetes, with onset at any age, but predominantly under the age of 30 years

• LADA (latent autoimmune diabetes of adulthood) or ‘type 1.5 diabetes’—a slowly progressive form of type 1 diabetes mellitus. Patients are often diagnosed as type 2 diabetes, but have positive pancreatic islet antibodies, especially to glutamic acid decarboxylase (GAD). They do not immediately require insulin for treatment, are often not overweight, and have little or no resistance to insulin

• type 2 diabetes—a growing global epidemic linked to overweight and obesity, calorie-dense foods, physical inactivity and increasing levels of stress. It is closely associated with an increased risk of cardiovascular disease. Although historically type 2 diabetes has been a condition of the elderly, because of changing lifestyle patterns we are now seeing type 2 diabetes in preteens. The long-term health and economic implications of the rising incidence and falling age of onset are enormous

• gestational diabetes—a transient but significant form of diabetes; 3–5% of pregnant women will develop gestational diabetes at week 24–28 of pregnancy. Blood glucose levels usually return to normal after the delivery, but women who have gestational diabetes have a 30–50% chance of developing type 2 diabetes within 20 years.¹

The role of the general practitioner is in identifying those at risk of diabetes and advising on preventive and early intervention strategies when impaired glucose tolerance, prediabetes or diabetes is identified.

Once a diagnosis of diabetes is established, management of diabetes is aimed at secondary prevention strategies through control of blood sugar levels, correction of micronutrient deficiencies and active risk factor management. The long-term effects of diabetes are largely due to its effect on blood vessels leading to both micro and macro vascular disease.

RISK FACTORS AND PRIMARY PREVENTION

In order to establish advice for patients on how to prevent or delay the onset of diabetes, it is important to:

• understand the aetiology, and

• identify and assess any avoidable or modifiable risk factors.

AETIOLOGY

Type 1 diabetes

Type 1 diabetes constitutes around 5–10% of diabetes cases. Aetiological factors are the following:

• autoimmune response—thought to be triggered by exposure to environmental agents such as viruses and toxins in individuals with an inherited predisposition

• genetic factors—there is some association of type 1 diabetes with other autoimmune conditions within individuals and families, such as coeliac disease, autoimmune thyroiditis,² Addison’s disease and pernicious anaemia. Human leucocyte antigen (HLA) class II association: HLA DR4-DQ8 and/or DR3-DQ2 are positively associated with diabetes type 1, while DR15-DQ6 (B*0602) is negatively associated.

Type 2 diabetes

Type 2 diabetes constitutes around 90–95% of cases of diabetes. Aetiological factors are the following:

• physical inactivity

• inherited predisposition

• stress (allostatic load)

• inflammation

• environmental factors

• calorie-dense diet.

Type 2 diabetes, being strongly related to lifestyle, is most common in affluent countries, where there is abundant food along with sedentary occupations and a significant uptake of labour-saving devices. Within those affluent countries, however, type 2 diabetes is more common among lower socioeconomic groups, where poor-quality food, social disadvantage and poorer education have their impact. In either case, the cause of the condition being largely lifestyle related also means that it is preventable and can be managed with appropriate and sustained lifestyle change. To illustrate how important simple lifestyle factors are in diabetes prevention, never smoking, having a BMI < 30, exercising moderately for 3.5 hours per week and following a few healthy dietary principles (high intake of fruit, vegetables and wholegrain bread, and low meat consumption) compared with not having any of those four factors was associated with a 93% reduced risk of developing type 2 diabetes over 8 years of follow-up.³

The challenge in type 2 diabetes management, as with other chronic illnesses related to lifestyle, is to motivate the patient to make the necessary changes. From a sociological perspective, the solution also requires that we address the social, economic and educational conditions that make it easier for a condition like type 2 diabetes to flourish. This needs motivated healthcare practitioners as well as educators, health promoters, legislators and policy makers. No single solution will work in isolation from the others.

Gestational diabetes

The hormones responsible for promoting fetal growth and development increase markedly in the last 20 weeks of pregnancy. Human placental lactogen in particular has anti-insulin effects. Despite higher insulin levels in the last trimester, there is a reduction in peripheral insulin sensitivity and higher basal hepatic glucose output.

Prediabetes and metabolic syndrome

Prediabetes is a state in which the body does not respond properly to insulin, so blood glucose levels are higher than normal, but not in the range for a diagnosis of diabetes. It is generally asymptomatic. Progression to a diagnosis of diabetes is not inevitable.

FIGURE 26.1 Long-term complications of diabetes

Metabolic syndrome is a recognised precursor to the development of type 2 diabetes. A diagnosis of metabolic syndrome requires three of the risk factors listed in Box 26.1 to be present.⁴

Significance of metabolic syndrome

Metabolic syndrome is a cluster of risk factors that increase the risk of developing diabetes, heart disease and stroke. It is also known as syndrome X, dysmetabolic syndrome and insulin resistance syndrome. Incidence increases with age. It is thought to be the result of a combination of genetic predisposition and lifestyle factors, including dietary and exercise habits.

PRIMARY PREVENTION

Nutritional and environmental

Pre-conception counselling and pregnancy

Maternal malnutrition and overnutrition during pregnancy are associated with subsequent type 2 diabetes in the offspring.⁵ Primary prevention needs to start with pre-conception counselling of women planning pregnancy, with advice on exercise and nutrition to maintain optimal weight and nutritional status during the pregnancy.

Infant supplements

A systematic review of observational studies found that giving infants vitamin D supplements could protect them from type 1 diabetes.⁶ Infants given the supplement had an almost 30% reduced risk of diabetes compared with those who were not supplemented. This is particularly important in breastfed infants of vitamin-D-deficient mothers.

Weight management

Preventing or reversing metabolic syndrome involves weight loss and waist circumference reduction through diet and increased activity, and maintaining goal levels of blood pressure, lipids and lipoproteins and blood glucose. BMI per se is now seen as a less accurate marker of cardiovascular risk. It is not just the presence of excess weight but the pattern of weight distribution that is important. Abdominal or ‘apple’ obesity is the pattern associated with greater risk. The so-called ‘pear’ distribution of fat, mostly around the hips and legs, is less of a problem than the apple distribution. The measurement to determine which category a patient falls into is the waist–hip ratio. If this is above 1.0 for women or 0.9 for men, the person is said to have the apple distribution of fat; below these figures the person would be classified as having the pear distribution.

The mainstays of primary prevention of diabetes are:

• a healthy diet from conception onwards, including a wide range of regular physical activity

• avoidance of sedentary activities

• maintenance of a healthy weight

• moderate alcohol consumption

• avoidance of smoking

• avoidance of environmental toxins.

Case detection

Proactive screening of asymptomatic patients

There is an asymptomatic phase of undetected diabetes mellitus that provides an opportunity for early detection, reducing the incidence of long-term complications. Microvascular complications such as retinopathy, neuropathy and renal disease are commonly already present at the time of diagnosis of type 2 diabetes.

The following groups of asymptomatic patients should be tested:⁷

• individuals over 55 years of age

• people aged 45 or older who have one or both of the following risk factors:

• obesity with BMI > 30

• hypertension

• Aboriginals and Torres Strait Islanders aged 35 or older

• certain high-risk non-English-speaking background groups aged 35 or older (specifically Pacific Island people, people from the Indian subcontinent or of Chinese origin)

• all people with impaired glucose tolerance or impaired fasting glucose

• all people with clinical cardiovascular disease (myocardial infarction, stroke, angina)

• women with polycystic ovary syndrome who are obese

• patients taking antipsychotic drugs

• women with a past history of gestational diabetes.

FIGURE 26.2 Pear body

FIGURE 26.3 Apple body

Blood glucose level

The test of choice for diagnosis is fasting plasma glucose performed in an accredited laboratory. Random measures may be used.

Interpretation of blood glucose level (BGL) results:

• < 5.5 mmol/L—diabetes unlikely

• ≥ 7.0 mmol/L or more fasting or ≥ 11.1 mmol/L random—diabetes likely

• 5.5–6.9 mmol/L fasting, or 5.5–11.0 mmol/L random—perform a glucose tolerance test (GTT).

Re-testing should be performed under the following circumstances:

• on a different day, to confirm a BGL test suggesting a diagnosis of diabetes

• 1 year later for people who have an initial test suggesting diabetes that is not confirmed on the subsequent test

• each year for people with impaired GTT or impaired fasting glucose

• every 3 years for people in high-risk groups with negative screening tests.

People in high-risk groups with negative screening blood glucose tests are also at high risk for cardiovascular disease and should be encouraged to reduce their cardiovascular risk factors.

Glucose tolerance test

People found to have impaired glucose tolerance, where glucose levels are above normal but fall short of a diagnosis of diabetes, are at higher risk of later developing type 2 diabetes and also at higher risk of cardiovascular disease. Approximately one-third of people with impaired glucose tolerance will develop type 2 diabetes.

MANAGEMENT

INITIAL ASSESSMENT

History

Initial assessment of the patient with diabetes involves a comprehensive medical, social and lifestyle history:

• food diary for 3–7 days to assess current eating patterns

• exercise diary—including current patterns of exercise frequency, duration and intensity

• psychosocial assessment (stress, anxiety, depression)

• current medication and supplements

• tobacco and alcohol consumption

• family history of diabetes, cardiovascular disease, osteoporosis, coeliac disease and hyperlipidaemia

• review results of recent investigations where available.

Examination

Comprehensive physical examination, including:

• blood pressure, cardiovascular assessment

• peripheral neurological assessment

• height, weight, BMI

• waist circumference

• feet—ulcers, neuropathy, peripheral vascular disease

• urinalysis (especially looking for asymptomatic urinary tract infection and microalbuminuria)

• visual acuity, retinal fundoscopy

Laboratory tests and further investigations:

• fasting BGL

• HbA_1c every 6 months

• urinary albumin/protein

• full blood examination including haemoglobin and white cell count

• C-reactive protein

• homocysteine (cardiovascular risk)

• thyroid function tests (TFT) (TSH and free T₄)

• fasting lipids (cholesterol and HDL)

• micronutrient assessment (especially iron, folate, vitamin B₁₂, B₆)

• coeliac serology (association between type 1 diabetes and coeliac disease—1 in 20 people with type 1 diabetes have coeliac disease and as many as 1 in 10 test positive for transglutaminase IgA autoantibodies)

• baseline retinal and visual assessment

• bone densitometry for patients aged over 40.

Type 1 or type 2?

Blood tests can help distinguish between type 1 and type 2 diabetes.

• Tests for islet cell and anti-GAD antibodies are positive in 90% of patients with type 1 diabetes.

• C-peptide levels would be abnomally low in type 1 and normal in type 2 diabetes.

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