The rules seem simple:

1. Control blood glucose levels (BGLs) before breakfast and the evening meal by adjusting the long-acting insulin/s.
2. Control BGLs after meals by; counting your carbs, checking your BGL and injecting your quick acting insulin.

Rule 1: Rules are flexible!
However, type 1 diabetes “doesn’t play by the rulesâ€. In people without diabetes, blood glucose is regulated continuously and in real time by the alpha and beta cells in the pancreas and by cells inside the brain. These three regulators can push blood glucose up or pull blood glucose down through the hormones insulin (from beta cells) and glucagon (from the alpha cells) and through the sympathetic nervous system. All three systems work directly on the liver to increase glucose release and insulin works on fatty and muscle tissues, increasing glucose uptake. All are adjusted continuously, immediately and automatically and all can be switched on or off very quickly (within minutes).

An imperfect science
In type 1 diabetes, all three controllers go wrong – the beta cells have been destroyed, the alpha cells don’t work properly and if there is any nerve damage the sympathetic nervous system is also affected. The main way we try to control blood glucose (insulin injections) has greatly improved since the 1920s but is still a very inadequate replacement.

• Generally, blood glucose is measured at one or more times a day and even with ‘continuous blood glucose monitoring’ there is a lag between a change in blood glucose and a change in the continuous glucose monitoring system (CGMS) reading.
• The blood glucose meter might read 6.2 mmol/L but that doesn’t mean that the blood glucose is 6.2 but something between 6.2±15–30% (i.e. 4.3 to 8.1).
• The insulin is adjusted one or more times a day but even with insulin pumps, insulin is injected under the skin and takes some time to be absorbed and passed through the blood stream to the body’s organs where it works.
• Once given, the insulin can’t be stopped and will keep working for some time, even if the blood glucose is low.
• There’s considerable variation in carbohydrate absorption from day to day, even if the same amount and type of carbohydrate is eaten at the same time of day.

People with type 1 diabetes don’t have a continuous, accurate, real time monitor of blood glucose and they don’t have systems to control it adequately. Even if blood glucose monitoring were perfect, blood glucose would still vary a lot over the 24-hour period. For example, in someone without diabetes, 80% of readings will lie within 10% of the average. In someone with diabetes, 80% of the values vary a lot more. For example, in someone with an average BGL of 9.1, 80% of values would lie between 4.6 and 16.6 (and with 10% lower than 4.6 and 10% over 16.6).

Allow for chance and change
It’s certainly true that the rules aren’t railway lines that will always lead you to perfect blood glucose control, but I’d suggest you use them as general guidelines that will help you reduce some of the blood glucose swings.

Dr Pat Phillips, MBBS, MA, FRACP, Dip Ed Health Economics, is Editor-in-Chief of Conquest and Past Director of the Diabetes Centre and Endocrinology, Queen Elizabeth Hospital & Health Service

This article was originally published in Conquest magazine published by Health Publishing Australia