Diabetes and insulin

Over time, blood glucose levels above the normal range can damage your eyes, kidneys and nerves, and can lead to other serious health problems. Diabetes is one of the fastest-growing chronic conditions in the world. The three main types are type 1, type 2 and gestational diabetes.

Type 1 diabetes#

Type 1 diabetes develops when the cells of the pancreas stop producing insulin. Without insulin, glucose cannot enter the body’s cells for energy, so it builds up in the blood and the person becomes extremely unwell. Type 1 diabetes is life-threatening if insulin is not replaced, and people with the condition need to inject insulin for the rest of their lives.

It often occurs in children and people under 30, but it can develop at any age. This condition is not caused by lifestyle factors. Its exact cause is not known, but research suggests that something in the environment can trigger it in a person who has a genetic risk: the body’s immune system attacks and destroys the insulin-producing beta cells of the pancreas, treating them as foreign. Most people diagnosed with type 1 diabetes do not have a family member with the condition.

Type 2 diabetes#

Type 2 diabetes develops when the pancreas does not make enough insulin and the insulin that is made does not work as well as it should (also known as insulin resistance). As a result, glucose rises above normal levels in the blood. Around half the people with type 2 diabetes do not know they have it, because they have no symptoms.

Type 2 diabetes (once known as adult-onset diabetes) affects 85 to 90% of all people with diabetes. People who develop it are very likely to have a family member with the condition. It is considered a lifestyle condition because being overweight and inactive increases the risk, and people from some ethnic backgrounds are more likely to develop it.

It can often be managed at first with healthy eating and increased physical activity. Over time, most people with type 2 diabetes will need diabetes tablets to help keep their blood glucose in the target range, and regular blood glucose monitoring may be needed to check how well treatment is working. The point at which tablets are started varies from person to person, and about 50% of people with type 2 diabetes need insulin injections within 6 to 10 years of diagnosis.

Gestational diabetes#

Gestational diabetes occurs in about 5 to 10% of pregnant women and usually goes away after the baby is born. Women who have had gestational diabetes have an increased risk of developing type 2 diabetes later in life.

Management includes seeing a dietitian for healthy-eating strategies to help manage blood glucose, and, where possible, regular exercise such as walking. Measuring blood glucose with a meter shows whether these strategies are keeping levels in the recommended range. Some women may also need to inject insulin to manage their blood glucose until their baby is born.

What insulin does#

Insulin is a hormone the body makes to keep blood glucose within the normal range. It is produced by the beta cells in the pancreas, and its main job is to move glucose from the bloodstream into the body’s cells to make energy. If you do not have enough insulin, glucose builds up in the bloodstream instead of getting into your cells.

• With type 1 diabetes, the body makes no insulin, so insulin has to be injected every day to stay alive.
• With type 2 diabetes, the body does not make enough insulin, or the insulin it makes does not work well, so insulin injections are sometimes needed to manage blood glucose.

People with type 1 diabetes must inject insulin every day, often up to 4 or 5 times a day. Some use a pump, which means inserting a new cannula (a very fine plastic tube) under the skin every 2 to 3 days. People with type 2 diabetes may also need to start insulin when diet, physical activity and tablets no longer keep their blood glucose under control.

Starting on insulin#

Having to start injecting insulin can feel frightening, but it is much easier than most people imagine. There are different devices that make insulin delivery simple, and pen needles and cannulas are very fine. Many people feel much better once they start insulin.

If you need to start insulin, your doctor or diabetes nurse educator can provide education and support. They will teach you about:

• the type and action of your insulin
• how, where and when to inject
• how to rotate your injection sites
• where to get your insulin and how to store it safely
• how to manage low blood glucose
• how to keep a record of your blood glucose levels and insulin doses

Insulin doses usually do not stay the same as your starting dose. Your doctor or diabetes nurse educator will help you adjust them, and regular blood glucose monitoring and recording is an important part of this. Your doses may need to change for many reasons, such as more or less exercise, a change in diet or medication, illness, or weight gain or loss, so see your diabetes care team regularly for review.

When you start insulin it also helps to be reviewed by a dietitian to understand how carbohydrates and insulin work together. If you have type 1 diabetes, learning to count carbohydrates and match your insulin to the food you eat is the ideal way to manage it, and your mealtime doses may vary from meal to meal and day to day.

Types of insulin#

Insulin is grouped according to how long it works in the body. Rapid- or short-acting insulin helps reduce blood glucose at mealtimes, while intermediate- or long-acting insulin helps manage the body’s general background needs. Both help manage blood glucose levels, and the five types range from rapid- to long-acting.

Some types of insulin look clear, while others are cloudy. Check with your pharmacist whether the insulin you are taking should be clear or cloudy. Before injecting a cloudy insulin, gently roll the pen or vial between your hands so the insulin is evenly mixed (until it looks milky). If your insulin is meant to be clear, do not use it if it has turned cloudy. Many people need both rapid- and longer-acting insulin, and everyone needs a different combination.

Rapid-acting insulin#

Rapid-acting insulin acts quickly after a meal, similar to the body’s natural insulin, peaking within about 3 hours and lasting up to 5 hours. This reduces the risk of a low blood glucose (below 4 mmol/L). When you use it, you must eat immediately or soon after you inject. Examples include Fiasp and NovoRapid® (insulin aspart), Humalog® (insulin lispro) and Apidra® (insulin glulisine). Fiasp is a newer rapid-acting insulin with a faster onset, designed to improve blood glucose after a meal.

Short-acting insulin#

Short-acting insulin takes longer to start working than the rapid-acting insulins. It begins to lower blood glucose within 30 minutes, so you need to inject 30 minutes before eating. It has its maximum effect 2 to 5 hours after injection and lasts for 6 to 8 hours. Examples include Actrapid® and Humulin® R.

Intermediate- and long-acting insulin#

Intermediate- and long-acting insulins are often called background or basal insulins. The intermediate-acting insulins are cloudy and need to be mixed well; they begin to work about 60 to 90 minutes after injection, peak between 4 and 12 hours, and last 16 to 24 hours. Examples include Protaphane® and Humulin® NPH (human isophane insulins).

Long-acting insulins include:

• Lantus® (glargine insulin), a slow, steady release with no clear peak; one injection can last up to 24 hours. It is usually given once a day but can be taken twice daily.
• Toujeo (glargine insulin), which has a strength of 300 units per ml, three times the concentration of standard insulin. It is given once a day, lasts at least 24 hours, and gives a slower, steadier glucose profile, especially overnight. It comes in a disposable pen only and should not be confused with regular Lantus, which is 100 units per ml.
• Levemir® (detemir insulin), a slow, steady release with no clear peak that can last up to 18 hours and is usually injected twice daily.

Although these insulins are long-acting, they are clear and do not need mixing before injecting.

Mixed insulin#

Mixed insulin contains a pre-mixed combination of a very rapid-acting or short-acting insulin together with an intermediate-acting insulin. Examples include NovoMix® 30 (30% rapid, 70% intermediate), Humalog® Mix 25 and Mix 50, Ryzodeg 70:30 (long-acting and rapid), and Mixtard® 30/70 and 50/50 and Humulin® 30/70 (short and intermediate).

Insulin strength#

In many countries, the standard strength of these insulins is 100 units per ml, though some countries use different strengths. The exception is the once-daily long-acting insulin Toujeo, which has a strength of 300 units per ml. Do not switch between Lantus and Toujeo without consulting a health professional.

Insulin delivery devices#

The main choices are syringes, insulin pens and insulin pumps.

Syringes come in 30-unit (0.3 ml), 50-unit (0.5 ml) and 100-unit (1.0 ml) sizes, and the size you need depends on your dose, for example, it is easier to measure 10 units in a 30-unit syringe and 55 units in a 100-unit syringe. The needles range from 6 to 8 mm. Insulin syringes are single-use only, and in some countries they may be available free or subsidised through national diabetes programmes. Your doctor or diabetes nurse educator can help you choose the right syringe and needle size.

Insulin pens are now used by most adults instead of syringes, for greater convenience. Pens are designed to work with a particular brand of insulin. Disposable pens come with the insulin cartridge already inside and are thrown away when empty, when they have been out of the fridge for one month, or when the use-by date is reached. Reusable pens take a 3 ml insulin cartridge (100 units per ml); when finished, a new cartridge is inserted, and any cartridge should be discarded one month after it is first used if insulin remains. Your doctor or diabetes nurse educator can advise on the right pen for you.

Pen needles screw onto the pen and come in lengths from 4 to 12.7 mm, although research recommends 4 to 5 mm needles. The thickness (gauge) also varies, the higher the gauge, the finer the needle. Use a new pen needle for each injection, and ask your diabetes nurse educator to show you the correct technique.

Insulin pumps are small programmable devices worn outside the body that hold a reservoir of insulin and deliver it into the fatty tissue (usually the abdomen) through fine tubing called an infusion set. Only rapid-acting insulin is used in a pump. The infusion set has a fine needle or flexible cannula inserted just below the skin, which is changed every 2 to 3 days. The pump is programmed by the user and their health professional to deliver small continuous amounts of insulin between meals, and the user can instruct it to deliver a burst of insulin when food is eaten, much as the pancreas does in people without diabetes.

An insulin pump is not suitable for everyone, so discuss it with your diabetes care team first. The cost of a pump and its disposable extras may be covered or subsidised in some countries through private health insurance or national diabetes programmes.

Injecting insulin#

Insulin is injected through the skin into the fatty tissue known as the subcutaneous layer. It should not go into muscle or directly into the blood, as this changes how quickly it is absorbed.

Absorption varies depending on where you inject. The abdomen absorbs insulin fastest and is used by most people; the upper arms, buttocks and thighs absorb more slowly and can also be used. This variation can cause changes in blood glucose levels.

Insulin absorption is increased by:

• injecting into muscle, which can cause blood glucose to drop too low
• injecting into an exercised area, such as the thighs or arms
• high temperatures, for example from a hot shower, bath, spa or sauna
• massaging the area around the injection site

Insulin absorption is delayed by:

• over-use of the same injection site, which makes the area lumpy or scarred (lipohypertrophy)
• insulin that is cold, for example straight from the fridge
• cigarette smoking

Disposing of sharps#

Used syringes, pen needles, cannulas and lancets must be disposed of in an approved sharps container, which is puncture-proof and has a secure lid. These containers are usually yellow and are available through pharmacies, local councils and diabetes organisations. Disposal procedures vary by area, so contact your local council or a diabetes organisation for information and help.

Storing insulin#

Store insulin correctly:

• Keep unopened insulin on its side in a fridge, with the temperature between 2 and 8°C (46.4°F), and make sure it does not freeze.
• Once opened, keep it at room temperature (less than 25°C (77°F)) for no more than one month, then dispose of it safely.
• Avoid direct sunlight.

Extreme hot or cold temperatures can damage insulin so it no longer works properly. It must not be left where the temperature is over 30°C (86°F), a car can easily get this hot, so do not leave insulin there. Insulated carry bags are available for transporting insulin.

Do not use insulin if:

• cloudy insulin has lumps or flakes, or deposits that cannot be dissolved by gentle rolling
• a vial, penfill or cartridge has been used, or out of the fridge, for longer than one month
• clear insulin has turned cloudy
• the expiry date has passed, or it has been frozen or exposed to high temperatures

Keeping a record of your blood glucose levels helps you and your healthcare professional know when your insulin dose needs adjusting.

Key points#

• Over time, high blood glucose can damage your eyes, kidneys and nerves; the main types of diabetes are type 1, type 2 and gestational.
• Type 1 diabetes is not caused by lifestyle factors, and people with it need insulin for life.
• Half the people with type 2 diabetes have no symptoms; being overweight and inactive increases the risk.
• Insulin is grouped by how long it works, store it correctly, rotate injection sites, and keep a record of your levels and doses.

Where to get help and trusted information#

For evidence-based global health guidance, see Source: World Health Organization (WHO).