Insulin Basics: Types, Timing and Correct Injection Technique
Starting insulin is often treated as a failure or a last resort. It is neither. It is simply replacing a hormone the body no longer makes in sufficient quantity, and in type 1 diabetes it is not optional at all. Getting good results depends heavily on understanding what each type does and on technique that is rarely taught properly.
How the body normally releases insulin
A healthy pancreas does two things at once. It releases a small continuous amount of insulin through the day and night, called basal secretion, which controls glucose production by the liver between meals. It then releases a sharp burst with each meal, called bolus secretion, to handle the incoming carbohydrate.
Insulin regimens try to copy this pattern, and the names of the insulin types map directly onto it.
The main types
Rapid-acting analogues such as lispro, aspart and glulisine. Onset around 10 to 20 minutes, peak at 1 to 2 hours, duration 3 to 5 hours. Taken with meals.
Short-acting or regular human insulin. Onset 30 to 60 minutes, peak 2 to 4 hours, duration 6 to 8 hours. Needs to be taken about 30 minutes before eating, which is the most common source of error with this type.
Intermediate-acting NPH. Onset 1 to 2 hours, peak 4 to 10 hours, duration 12 to 18 hours. Usually twice daily. The pronounced peak is what causes mid-afternoon and nocturnal hypoglycaemia.
Long-acting analogues such as glargine and detemir. Duration roughly 20 to 24 hours with little or no peak, usually once daily.
Ultra-long-acting such as degludec. Duration beyond 40 hours, with flexible timing.
Premixed insulins, for example 30/70. Convenient at two injections a day but inflexible, since the fixed ratio demands consistent meal size and timing.
Common regimens
- Basal only: a long-acting insulin at bedtime added to oral medication. The usual starting point in type 2 diabetes
- Basal plus: basal insulin with a rapid-acting dose at the largest meal
- Basal bolus: basal insulin plus rapid-acting insulin at every meal. The most flexible and the standard in type 1 diabetes
- Premixed twice daily: fewer injections, less flexibility
- Insulin pump: continuous rapid-acting delivery with meal boluses
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Injection technique, where most problems hide
Sites. The abdomen, avoiding a two-finger-width circle around the navel, absorbs fastest and most predictably. The outer thigh and buttock absorb more slowly. The outer upper arm is intermediate. Use the same body region for the same time of day, for example abdomen for meal doses and thigh for the bedtime basal, so absorption stays consistent.
Rotation. Rotate within the region by at least a finger’s width from the last injection, moving systematically rather than randomly. Not rotating causes lipohypertrophy, which brings us to the single biggest hidden cause of erratic control.
Lipohypertrophy is a rubbery, often painless swelling of fat under repeatedly injected skin. It is less painful to inject into, so people keep using it, and insulin absorbed from it is erratic and unpredictable. Feel your injection sites regularly for soft lumps, and show them to your doctor. Switching away from an affected site can require a dose reduction of 20 percent or more, so it must be done with medical supervision to avoid hypoglycaemia.
Needle length. 4 mm pen needles are suitable for nearly all adults, including those with obesity, and inject at 90 degrees without a skin fold. Longer needles risk intramuscular injection, which speeds absorption unpredictably.
Technique steps. Use a new needle each time; reused needles bend, blunt and cause tissue damage. Prime with two units until a droplet appears, to clear air. Insert, press the plunger fully, then count to ten before withdrawing, otherwise insulin leaks back out. Dispose of needles safely.
Cloudy insulins, meaning NPH and premixes, must be gently rolled and tipped about twenty times until uniformly milky. Shaking creates bubbles. Clear insulins need no mixing.
Storage
Unopened vials and pens go in the refrigerator between 2 and 8 degrees, never the freezer; frozen insulin is destroyed and must be discarded. An in-use pen can stay at room temperature for about 28 days depending on the product, and injecting cold insulin stings. Keep insulin out of direct sunlight and out of hot vehicles. In hot climates without reliable refrigeration, a clay pot cooler or an insulated pouch is better than nothing.
Hypoglycaemia
Know the symptoms: sweating, shakiness, hunger, palpitations, anxiety, confusion, irritability, blurred vision. Treat with 15 grams of fast carbohydrate, for example three teaspoons of sugar or glucose in water or half a cup of juice, wait 15 minutes, retest, and repeat if still low. Follow with a longer-acting snack if the next meal is more than an hour away.
Hypoglycaemia unawareness, where warning symptoms disappear, is dangerous and needs medical review. Always carry fast sugar, and make sure family members know what to do and when to call for help.
Dose adjustment
Doses are adjusted gradually, usually by small increments every three days based on patterns rather than single readings. Never change your own doses substantially without guidance, and never skip insulin when unwell: illness usually raises requirements, and omitting insulin in type 1 diabetes can cause diabetic ketoacidosis within hours.
This is general information. Insulin type, dose and timing must be individualised by your doctor or diabetes team.