1. Match your insulin or medicine program to your needs.
The “peaks and valleys” in your insulin should coincide with the peaks and valleys in your blood glucose levels. This usually means utilizing a basal–bolus insulin approach — having a long-acting, or basal, insulin working at a low level throughout the day and night, and rapid-acting, or bolus, insulin at each meal or snack. Most adults experience a dawn phenomenon, in which more basal insulin is needed during the early morning hours, and less in the middle of the day. Daytime doses of intermediate-acting insulin, such as NPH, peak in the middle of the day or too early at night and increase the risk for hypoglycemia at these times.
Mealtime insulin should match your typical blood glucose rise caused by dietary carbohydrate. Most starchy and sugary foods cause a rapid blood glucose rise, with a peak occurring about an hour after eating. Rapid-acting insulin analogs do a nice job of covering the rapid blood glucose rise and then dissipating before they can cause hypoglycemia later on. Regular insulin tends to peak too late and last too long, increasing the risk of hypoglycemia several hours after eating.
For those taking pancreas-stimulating oral medicines, be aware that some — glimepiride, glipizide, glyburide, chlorpropamide, tolazamide, and tolbutamide — work constantly (whether you are eating or not), while others — nateglinide and repaglinide — work for a short time (just after eating). Obviously, nateglinide and repaglinide are less likely to cause between-meal lows.
2. Set an appropriate target.
Work with your doctor to determine an ideal premeal blood glucose level. This is the level that you aim for when making your mealtime dosing decisions. For most people with diabetes who take insulin, this is usually 100, 120, or 140 mg/dl. A target below 100 mg/dl does not leave much margin for error and may result in a greater frequency of low blood glucose. For those with Type 2 diabetes who use oral medicines, targets of 80, 100, or 120 mg/dl are common.
3. Take a look at your schedule.
Are you eating at the times your insulin or medicine is working its hardest? For those using an insulin pump, this is not generally an issue as long as the basal rates are set properly. For those using a long-acting basal insulin, there may be a tendency for the blood glucose to drop gradually during the daytime, so it will be necessary to eat at regular intervals. For those using daytime NPH or Lente, meal timing is a major issue: These insulins begin to work hard approximately four hours after injection, so carbohydrates must be consumed in specific amounts at specific times. For those taking sulfonylureas (glimepiride, glipizide, glyburide, chlorpropamide, tolazamide, and tolbutamide), it is not a good idea to skip or delay meals since the medicine is stimulating extra insulin production throughout the day and night.
4. Use caution when “covering” high blood glucose.
Each unit of insulin will cause the blood glucose to drop by a certain amount, but the amount may vary by time of day. For many people, each unit lowers the blood glucose more at nighttime than during the day. Make sure your “correction” doses take this into account.
Also, be certain to account for “unused” insulin (the amount that is still active from the previous dose). With rapid-acting insulin analogs, it usually takes about 3–5 hours for the insulin’s activity to fade completely. Regular insulin takes about 5–6 hours. A blood glucose reading taken 2 hours after a meal can be misleading since the insulin still packs a good deal of punch and the blood glucose should continue to drop. (See “Accounting for Unused Insulin” for guidelines on how to take still-active insulin into account.)