Diabetes - how it affects athletes and ways to combat it

Diabetes – how athletes can beat the sugar blues

Contrary to popular belief, the soaring incidence of diabetes is not confined to the elderly or obese; athletes can and do suffer from diabetes and the chances are that some of you reading this will go on to develop the condition in years to come. However, as John Bye explains, the right management techniques mean that sufferers can still train and compete at the highest level

In 1997 Steve Redgrave was diagnosed with type 2 diabetes mellitus. In 2000 he won his fifth consecutive Olympic gold; in doing so he proved that diabetic athletes can achieve great things with the right approach. As Sir Steve Redgrave’s case demonstrates, diabetes mellitus is not a problem restricted to the obese, as the popular press might have you believe. According to Diabetes UK, there are currently over 2m diagnosed and 750,000 undiagnosed diabetics in the UK, while according to the American Diabetes Association, the USA has 14.6m diagnosed sufferers, 6.2m undiagnosed sufferers and an astonishing 54m pre-diabetics (ie at risk)! This article aims to arm athletes and coaches with the following information about this increasingly common problem:

• The similarities and differences between the two types of diabetes mellitus, their causes, symptoms, diagnosis, complications and treatment;
• The need for pre-exercise screening of diabetics;
• The benefits and risks of exercise for people with diabetes;
• Some special considerations for athletes with diabetes;
• Sources of further information.

What is diabetes mellitus?

Diabetes mellitus is a condition in which the level of glucose in the blood is too high because the body is unable to process it properly due to either a lack of, or insensitivity to, the hormone insulin. Glucose is an essential fuel, derived from food, transported in the blood and used by the body’s cells. Without insulin, glucose cannot enter the cells, cannot be stored as glycogen and cannot be used as fuel. We therefore need insulin to survive. There are two types of diabetes mellitus – type 1 and type 2:

Type 1 – 10-15% of diabetics have type 1 diabetes mellitus (also called insulin-dependent diabetes mellitus (IDDM) or juvenile-onset diabetes). Its onset is usually during childhood or adolescence, although it can occur at any age. It is thought to be caused by an autoimmune disorder in which the person’s own immune system mistakenly turns on and destroys the cells of the pancreas gland that are responsible for producing insulin. This immune attack stops the body producing its own insulin and type 1 diabetics therefore depend on prescribed insulin.

Type 2 – around 90% of diabetics have type 2 diabetes (also called non-insulin dependent diabetes mellitus (NIDDM) or adult-onset diabetes). Although its exact causes are uncertain, it is linked to obesity (around 80% of type 2 diabetics are obese) and genetics (the identical twin of a type 2 diabetic has up to a 90% chance of developing the disease). Type 2 diabetes results from the following changes:

• The pancreas produces less insulin in response to glucose in the blood;
• Cells in the muscles, liver and fat become less sensitive to the insulin that is produced, so less glucose is taken out of the bloodstream into the cells;
• The liver produces more glucose than normal
  at rest.

Type 2 diabetes normally affects those over the age of 40, although, with increasing levels of obesity in society, the diagnosis is increasingly being made earlier. Treatment may require dietary control, tablets and/or insulin.

Symptoms, signs and diagnosis of diabetes mellitus

Both types of diabetes present with similar symptoms and signs although they are more severe, obvious and quickly progressing in type 1. Symptoms and signs include:

• Increased thirst, which can be difficult or impossible to quench;
• Increased urine production; going to the toilet more often, especially at night;
• Excessive tiredness;
• Weight loss;
• Recurrent fungal infections such as thrush;
• Problems with vision, eg blurring;
• Slow healing of wounds.

Athletes and their coaches should be careful not to attribute such symptoms to problems like overtraining, especially if they are persistent or progressive. It would be advisable for an athlete with any of the symptoms and signs described above to seek a medical opinion sooner rather than later.

The diagnosis of diabetes is made more likely by the presence of glucose in the urine (identified using a very quick and easy dipstick test) and confirmed by any one of the following blood tests:

• Blood glucose level more than 7.0mmol per litre after fasting for 8 hours.
• Blood glucose level more than 11.0mmol per litre on random sampling.
• Blood glucose level more than 11.0mmol per litre two hours after taking a special glucose-containing drink (the oral glucose tolerance test).

Complications of diabetes

Diabetes, especially if poorly managed, can lead to numerous complications. The short-term complications include the following, all of which can kill if left untreated:

• Hypoglycaemia – low blood glucose due to inadequate intake of food, excessive physical activity and / or overdose of diabetic drugs such as insulin;
• Diabetic ketoacidosis (DKA) – mainly affects type 1 diabetics; it requires urgent treatment to prevent coma and death;
• Hyperosmolar non-ketotic acidosis (HONK) – only affects type 2 diabetics. HONK requires urgent hospital treatment with intravenous fluid and insulin.

The long-term complications of diabetes mellitus include an increased risk of heart attack, stroke and damage to the blood vessels that supply the arms and legs, kidney failure, visual problems due to diabetic retinopathy, nerve damage leading to weakness, loss of sensation and (in combination with damage to blood vessels) diabetic foot ulcers. Foot ulcers are of particular concern to athletes; nerve damage can mean that an ill-fitting shoe or piece of grit in the shoe can damage the skin and start a foot ulcer without the athlete feeling anything. Diabetic athletes should therefore check their feet for signs of damage and their shoes for stones etc regularly. Of particular relevance to athletes is the fact that diabetes can also increase the risk of a number of musculoskeletal conditions (see table 1, below left).

Pre-exercise screening of diabetics

Diabetic patients are often advised to exercise because it can reduce the likelihood of the complications of diabetes. Unfortunately, exercise can also reveal or worsen some complications and screening should therefore be undertaken before diabetic people either start, or increase their level of, exercise. The screening process should identify any complications of the disease that could be revealed or worsened by exercise and also assess the individual’s current level of control over their diabetes. To these ends, a pre-exercise screening programme would typically include:

• A ‘glycosylated haemoglobin’ (HBA1C) blood test to assess how well the person has controlled their blood glucose over the previous few months;
• Examination of the cardiovascular system, including measurement of blood pressure and assessment of pulses in the arms and legs, and a test to check blood lipid profile;
• Examination of the eyes to identify any problems caused by diabetes;
• Examination of the nervous system of the upper and lower limbs to identify any loss of feeling or weakness due to nerve damage;
• A check for diabetic foot ulcers;
• Blood and urine tests to check kidney function.
  Diabetic people are at increased risk of ischaemic heart disease but may not experience the chest pain normally associated with it because of nerve damage caused by diabetes. The latest published advice suggests that an exercise stress test should be performed if the patient (2):
• will be undergoing vigorous activity (heart rate over 60% of maximum);
• has had type 2 diabetes for over 10 years or type 1 diabetes for over 15 years;
• is over 35 years old;
• has risk factors for coronary artery disease (eg high blood pressure, high cholesterol);
• has any of the cardiovascular, eye, kidney or nerve complications of diabetes.

Diet, exercise and drugs

The aim of diabetes treatment is closely to control blood glucose levels in order to prevent the short-term and long-term complications of the disease. Blood glucose should ideally be kept between 5 and 7mmol per litre although a level of less than 10 is fine in the two hours following a meal.

The management of diabetes is based on diet and exercise plus or minus drugs, depending on type and severity. Perhaps the most important point about the treatment of diabetes is that everyone is different. Athletes should get to know their diabetes and learn how it responds to exercise, food and medication by closely monitoring their blood sugar levels and adjusting their activity levels, diet and medication accordingly under appropriate guidance. It is important for diabetic athletes to work closely with their medical team, especially if the diagnosis of diabetes has been recently made or if control of blood glucose is or has been difficult.

Diet – all diabetics benefit from a diet high in complex carbohydrates and low in fat – not at odds with general sport performance recommendations! Some type 2 diabetics need no more than a good diet to achieve control of their diabetes (see box, above right, for some practical dietary advice).

Exercise – reduces the risk of developing type 2 diabetes and is generally of benefit to both types of diabetic. However, exercise can worsen or cause some of the short- and long-term complications of diabetes, but with care these risks can be minimised (see box, above right, for some practical advice). Type 2 diabetics can reverse some of the changes that result in the disease by taking regular exercise. The immediate effect of exercise on blood glucose depends on the intensity of the exercise – high intensity anaerobic exercise tends to increase blood glucose levels whilst long duration aerobic exercise decreases levels. Athletes should check their levels during training so that they know how different types of exercise affect them.

Drugs – type 1 diabetics always require treatment with insulin. In the vast majority of cases, prescribed insulin is taken by injection although inhaled insulin has recently become available. The drug treatment for type 2 diabetes is more complicated, with treatment in steps. Oral medicines (tablets) are given to reduce blood glucose if diet alone fails to. Insulin is only added if and when both oral medication and diet have failed to keep blood glucose levels within acceptable limits. It should be noted that athletes with a high calorie diet (required for heavy training programmes or for pre-competition carbohydrate loading) will struggle to control their type 2 diabetes with diet alone. The latest research also suggests that adequate good quality sleep, in addition to diet, exercise and drugs, is important in controlling type 2 diabetes (3).

Special considerations for athletes with diabetes

Therapeutic use exemption – insulin is on the current World Anti-Doping Association (WADA) Prohibited List and on the revised list, published in September 2006 to be implemented on 1st January 2007 (both lists are available on www.wada-ama.org). Therefore, to compete legally, diabetic athletes taking insulin need to obtain a Therapeutic Use Exemption (TUE).

TUE forms can be downloaded from www.100percentme.co.uk. The form then needs to be completed and signed by both the athlete and their doctor before being sent to the appropriate governing body. Check with your sport’s governing body if you are unsure where you need to send the form. Diabetic athletes should not compete until a TUE has been granted.

Travel – airline security restrictions mean that diabetic athletes should have a doctor’s note and a copy of their prescription in order that they can travel with insulin, needles and syringes and their blood glucose monitoring equipment. Travel across time-zones can affect blood glucose levels and meals and medication doses may need to be adjusted accordingly.

High-risk sports – the short-term complications of diabetes, especially hypoglycaemia, can increase the risk in sports such as paragliding, parachuting, scuba diving and rock climbing. Diabetic individuals who want to participate in such sports should always seek medical advice first and diabetic athletes may wish to consider purchasing a MedicAlert® Bracelet or similar to identify their condition to people in case they are taken seriously ill.

An ex-competitive cyclist, John Bye graduated in sports and exercise medicine and is now director of Alchemy Sports Consultancy

References
1. Br J Sports Med Feb 2003; 37: 30-35.
2. Clinical Sports Medicine (Brukner and Khan) Aug 2006; Ch 48: 842
3. Arch Intern Med Sep 2006; 166:1768-1774
4. Physician Sportsmed 2003; 31(5):29-41