Updated July 24, 2006

Getting Down to Basals

by Gary Scheiner, M.S., C.D.E.

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?

Basal options
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 insulins (NPH and Lente) 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. Long-acting insulin (Ultralente) provides basal insulin for 24–36 hours, but usually with a broad peak at 8–16 hours, followed by an extended drop-off in action. 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.

The chart titled "Basal Insulin Action" illustrates the approximate level of insulin in the bloodstream using various types of basal insulin programs.

Gary Scheiner is a diabetes educator with a private practice (Integrated Diabetes Services) near Philadelphia, and the author of Think Like A Pancreas: A Practical Guide to Managing Diabetes With Insulin. He has had Type 1 diabetes for 20 years, and he offers diabetes education and management consultations via phone, fax, and Internet to people throughout the world. Submit inquiries to gary@integrateddiabetes.com, or call (877) SELF-MGT.

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