Activities taking place at altitude are as safe for people with diabetes as those without the condition as long as the five following areas are given special consideration:
- carbohydrate absorption
- acute mountain sickness (AMS)
- blood glucose monitoring
- insulin and carbohydrate requirements
- existing complications
Carbohydrates may not be metabolised effectively at altitude. Altitude is defined as over 2500 metres above sea level. This may be caused by a problem with glucose transfer from the blood to the muscles. Evidence for this theory comes from the fact that ketoacidosis, resulting from high blood-glucose levels, is common at altitude. However, elevated blood-glucose levels may be explained by the normal response to activity and/or cold, which is to release glucose stored in the liver and encourage more glucose to be transported to the muscles. If the body does not have enough insulin, this glucose will not reach the muscles and will raise blood glucose levels further, potentially resulting in ketoacidosis. The exact cause remains uncertain and may be a combination of oxygen levels, temperature, reduced insulin intake (to prevent hypoglycaemia in the event of reduced carbohydrate intake) and intense energy demands. Whatever the cause, the outcome is the same: raised blood glucose levels. Frequent monitoring will provide early warning signs of hypo or hyperglycaemia.
Carbohydrate metabolism may also be affected by medications taken to prevent acute mountain sickness (AMS), which may induce ketoacidosis. The symptoms of altitude sickness, such as headaches and light-headedness, may also mask or reduce hypoglycaemic warning signs.
Whilst it is essential to monitor blood glucose levels to assess whether there is sufficient insulin and carbohydrate for activity, your electronic monitoring equipment may not be reliable. Most meters are only guaranteed for reliable readings up to a height of 5000m (research in 1996 suggested that readings may be unreliable over 2000m) and within a temperature range of 18 –30 degrees centigrade. Outside these ranges, meters can give incorrect high or low readings, or even stop working altogether. Check with your meter manufacturer about the height and temperature ranges of your meter. Keep meters close to the body for optimum temperature operation.
Without accurate blood glucose readings, it may be very difficult to adjust insulin and carbohydrate intake. While any activity may necessitate a change in insulin dose, it is particularly likely if the activity is prolonged, intense or in environments with unusually high or low temperatures. Reliable monitoring may indicate the need for changes to both short and long acting insulins. Mixed insulin may be unreliable at altitude - talk to your diabetes care team about this.
Existing complications, particularly retinopathy or peripheral neuropathy, require careful management. There is an increased risk of retinal haemorrhage at high altitude in those with retinopathy. In extreme temperatures, those with peripheral neuropathy may not be aware of injuries or frostbite that require immediate action.
Be overly cautious. There is no reason why people with diabetes should not participate in activities at altitude, but there may be changes in insulin and carbohydrate needs and this requires continuous monitoring.
If you control your diabetes with insulin or other oral hypoglycaemic agents then your planned activity should take into account the following:
- If you are likely to be some distance away from insulin supplies, frequent monitoring and planning for eventualities is the most important consideration for people on trekking, mountaineering or skiing trips. Take supplies and make contingency plans.
- Work your way up the mountains slowly. Start with moderate heights – not Everest. Find out how your diabetes is affected at lower altitudes before attempting prolonged or high treks. Gradual acclimatisation will reduce the incidence of acute mountain sickness and limit the need for medications, both of which may compromise your diabetes control.
- Injection sites should be away from areas used during activity (the stomach is ideal). Keep used needles in a suitable container for eventual disposal.
- Monitor as frequently as you can and keep monitoring and insulin equipment as close to optimum temperature as possible, using shelter, bubblewrap and body-warmth in cold environments, and ‘Frio’ or equivalent during hot days. Insulin becomes ineffective if frozen or if it goes above 25 degrees centigrade. Take a back-up meter and batteries. Cold hands make testing difficult, so wear gloves before you test. If the reading does not seem in keeping with the signs or symptoms you’re experiencing, then retest, aiming for the best possible monitoring conditions. Also, test your urine for glucose as an alternative to meters, which may be unreliable at altitude.
Signs & symptoms of hypoglycaemia: disorientation; trembling; sweating; blurred vision; extreme hunger; anxiety; pallor; rapid pulse – these may also be recognised by those around you
Symptoms of hyperglycaemia: thirst; excessive urination and extreme fatigue – take care as these may be dismissed as normal reactions to activity
- Fast-acting carbohydrate snacks and short-acting insulin should always be to hand. Keep supplies of food and insulin on your person: bags can be lost; things can fall out. Spread supplies amongst two or three people. Take more than you need whether for one day or longer if you expect to be away from your base camp for any length of time. If blood glucose levels rise, you may need short-acting insulin quickly.
- Altitude increases carbohydrate needs, whilst the cold can suppress the usual mechanisms for fat breakdown. Both these things may increase the risk of hypoglycaemia. Eat carbohydrate-rich breakfasts, such as cereals and toast and jam. Iron-rich foods (for example, red meats, poultry, fish and cereals fortified with iron) will increase haemoglobin (the oxygen transporter) and maximise oxygen uptake from the air. The absorption of iron can be enhanced by Vitamin C (eg by consuming fruit or fruit juice with meals). Tea can inhibit iron absorption.
- Hypoglycaemia can suppress shivering, one of the normal responses to cold, and increase the risk of hypothermia (body-core temperature lower than 35 degrees centigrade).
- The sun and/or altitude may increase fluid needs. Take adequate drinks and keep them liquid (not ice in freezing conditions) and wear a hat, sunglasses and sunscreen to prevent sunstroke.
If you have Type 2 diabetes treated by diet and activity or by metformin or glucobay alone (not treated with insulin), you are very unlikely to have a hypo. However, you may need food (particularly starchy food such as bread and potatoes) soon after you have been active.
Discuss emergency action with your team leader and members of your party beforehand. Never go off alone. Although hypoglycaemia is more common than hyperglycaemia, prompt treatment is necessary for both. Ketoacidosis (high blood-glucose levels leading to a build up of ketones) is dangerous if untreated and needs emergency treatment.