Clinical management of type 1 diabetes
The treatment of type 1 diabetes aims to restore the glucose equilibrium of the body to a state of near-normality, and to enable the person concerned to live the life he or she wishes to live. These aims require a reasonably stable balance between food, insulin and physical activity while management of diabetes is, as far as possible, arranged around the preferred lifestyle rather than lifestyle around the diabetes. Insulin therapy imitates natural secretion of insulin from the pancreas by supplying constant background levels of insulin and rapid peaks when food is consumed. This is most commonly achieved by multiple injections of long- and short-acting insulin, but can be more reliably obtained by continuous subcutaneous insulin delivery via a portable external device. Glucose control can be monitored in the short term by finger-prick blood testing or by subcutaneous sensors, and in the longer term by measurement of HbA1c; good control has been shown to protect against long term microvascular complications. Successful control of diabetes depends upon the coping style of the individual, their circumstances, good social support, and regular contact with the healthcare team. The reward is a long and healthy life.
Aims of therapy
The clinical features of type 1 diabetes at diagnosis are almost entirely due to loss of functional islet beta cells and the resulting insulin deficiency. Abnormalities of glucagon secretion and hormonal responses to hypoglycaemia appear later in the natural history of the condition. Insulin resistance is not a prominent feature, although affected individuals may coincidentally be insulin resistant because of overweight or other reasons. The over-riding goal of treatment is therefore to replace endogenous with exogenous insulin, and to adjust insulin delivery to food intake and physical activity in such a way as to minimise deviations in circulating glucose outside the physiological range. Diabetes is a self-treated condition which makes great demands upon the individual and those closely involved in their lives. Effective practical training in diabetes management and education in its wider implications are therefore major priorities, but need to be introduced in a staged manner over time. Emotional and social support are badly needed, especially in the early stages, and normal responses to diagnosis – grief, anger, depression and denial – may be aggravated by adverse social circumstances. Diabetes impacts upon many other aspects of life, such as starting a family, school or work, driving and choice of occupation, and advice, understanding and support are needed with all of these.
In health, the blood glucose rarely strays outside a range of 3.5–7 mmol/l (65–125 mg/dl). If blood glucose falls below about 3.5 mmol/l (65 mg/dl), typical symptoms of hypoglycaemia appear, although these may diminish over time, causing difficulties in recognition (hypoglycaemia unawareness) and impaired central nervous system function; hypoglycaemia avoidance is therefore a prime aim of therapy. Glucose levels in excess of about 10 mmol/l result in loss of glucose in the urine, leading to loss of salt and other electrolytes, excessive urine production and thirst. Uncontrolled glucose levels may progress to diabetic ketoacidosis if insulin is omitted or stress factors such as infection are encountered, but this is an avoidable condition. The risk of long-term harm to the cells lining larger arteries and small blood vessels increases in proportion to the level at which glucose exceeds the normal range, and treatment must aim to minimise this risk. Good glucose control in the early months and years of type 1 diabetes can prolong the life of remaining beta cell in the pancreas, which in turn makes longer term control easier to achieve.
Determinants of good glucose control
Despite the major challenge involved, many people with type 1 diabetes can and do manage to live a near-normal style of life with near-normal levels of blood glucose. The degree to which this can be achieved largely depends upon the motivation, coping style and circumstances of the person affected, together with the degree of social and professional support available to them. Other factors help to determine the ease with which good glucose control can be established. These include persistence of residual insulin production by the pancreas, which buffers changes in blood glucose, and the way in which hypoglycaemia affects the central nervous system, which varies markedly between individuals. The body’s sensitivity to insulin is greatest in the middle of the night, increasing the risk of hypoglycaemia at that time, but the need for insulin rises rapidly before waking. This is particularly marked in young people and is referred to as the 'dawn effect'. People are more sensitive to insulin after vigorous exercise, or in response to alcohol, and some women become more sensitive before menstruation. Conversely, the requirement for insulin rises with puberty and the adolescent growth spurt, during pregnancy, during infection, and in response to medications such as steroids. Emotional stress is a factor in some people. These issues can usually be anticipated and overcome, but they emphasise the need for patient education and easy access to skilled advice.
Although diet has been debated with considerable zeal and complexity, the basic principles are very simple. In general, the diet considered healthy for members of the general population is healthy for the person with diabetes. This will include restricted use of processed foods, animal fat and sugar, and increased use of fresh fruit and vegetables. Diet should also aim for maintenance of a healthy weight, and food intake needs to be adjusted to match the rate at which insulin enters the blood stream and changing energy requirements during the day. In practice, many people with diabetes achieve successful glucose control with quite varying patterns of food intake, and attention to diet may be more important than its precise content. For example, some people eat freely and adjust the insulin according to the meal they wish to consume. One variant of this approach is known as DAFNE (diet adjustment for normal eating).
In health, the pancreas makes less insulin during exercise, whereas release of other hormones such as adrenaline (epinephrine) is increased. These changes increase glucose output by the liver and make other fuels available to exercising tissues. Exercise also mobilises glucose receptors in muscle, which migrate to the cell surface, and render it more sensitive to insulin. This sensitivity persists after the exercise is finished, increasing the risk of hypoglycaemia. Injected insulin, in contrast, cannot be switched off during exercise, and short-acting insulin is absorbed more rapidly during exercise of the limb into which it has been injected. The risk and timing of hypoglycaemia is related to the level and duration of exercise, and avoidance strategies need to be adapted accordingly. Poorly controlled diabetes is associated with a reduced capacity for endurance sports.