To borrow a phrase from the late, great Rodney Dangerfield, “Basal insulin gets no respect.” Very few people know how to spell it correctly (basil? bazal? I mean, really!), and even fewer know what the heck it’s for. That’s a shame, because basal insulin (no “z”) is the foundation upon which insulin therapy is built.
Unlike its more famous little brother bolus, which is the rapid-acting insulin given to cover those delicious carbohydrates in our diet, basal’s job is much more mundane: to match the liver’s secretion of glucose into the bloodstream (and to prevent the liver from oversecreting glucose). Everyone’s liver does it, and a healthy pancreas responds by secreting a small amount of insulin into the bloodstream every few minutes.
How would we manage without basal insulin? Not so well. Because the liver is secreting glucose into the bloodstream continuously, a complete lack of insulin, even for just an hour or two, would result in a sharp rise in blood glucose level. Basal insulin also makes sure that the body’s cells are nourished with a steady supply of glucose to burn for energy. Without basal insulin, many of the body’s cells would starve for fuel. Some cells would resort to burning only fat for energy, and that leads to production of acidic waste products called ketones. The combination of dehydration (caused by high blood glucose) and heavy ketone production (from excessive fat metabolism) leads to a life-threatening condition known as diabetic ketoacidosis (DKA).
Suffice it to say that basal insulin is necessary for maintaining blood glucose control, not to mention survival. So where does one find basal insulin? How much is needed? And when should it be taken?
Each person’s basal insulin requirement is unique. It’s affected by factors such as body size, activity level, stage of growth, hormone levels, and the amount (if any) of internal insulin production from one’s own pancreas.
During a person’s growth years (up to age 21), basal insulin requirements tend to be heightened throughout the night. This is due to the production of hormones (growth hormone and cortisol) that stimulate the liver to release extra glucose into the bloodstream. After the growth years, production of these hormones is reduced and limited primarily to the predawn hours. The dawn effect, or dawn phenomenon, as this is called, results in an increased secretion of glucose by the liver in the early morning. As a result, basal insulin requirements in most adults tend to peak during the early morning hours.
To match these requirements, basal insulin can be supplied in a variety of ways. Intermediate-acting insulin (NPH) taken once daily will usually provide basal insulin around the clock, albeit at much higher levels 4–8 hours after injection and at much lower levels 16–24 hours after injection. Insulin glargine (brand name Lantus) and insulin detemir (Levemir) offer a relatively peakless insulin presence for approximately 24 hours, although the insulin level may wane a few hours earlier in some people. Insulin pumps deliver basal insulin in the form of tiny pulses of rapid-acting insulin every few minutes throughout the day and night. With a pump, the basal insulin level can be adjusted and fine-tuned to closely match the liver’s ebb and flow in glucose secretion.
Basal option 1: NPH at bedtime. The advantage of this program is the peak that occurs during the predawn hours — for those who need it. The disadvantages include the unpredictability of the peak and the potential for a blood glucose rise in the daytime and evening as the insulin action falls to very low levels at these times.