Hypoglycemia: What it is, How to Recognize its Onset, How to Avoid it
One of the central findings of the Diabetes Control and Complications Trial was the causal relationship between glycosylated hemoglobin and long-term diabetes complications. Specifically, the DCCT showed us that people who kept their blood glucose levels as close to normal as possible (aka "Tight control") had a markedly reduced incidence of long-term diabetes complications. The indicator of blood glucose level was the glycosylated hemoglobin (HbA1C) test, with lower HbA1C values being indicative of lower blood glucose levels during the proceeding several months.
Pump users everywhere welcomed the DCCT, for it provided additional validation for the contention that good control could reduce or eliminate long-term complications of diabetes. Perhaps less welcome was an ancillary finding of the DCCT that intensive insulin therapy was associated with a higher incidence of hypoglycemia. In their original report the authors of the DCCT noted that participants using intensive insulin therapy had up to a three-fold increased incidence of hypoglycemic episodes. Upon reviewing the data, however, the authors of the DCCT concluded that "the risk of severe hypoglycemia with intensive therapy is greatly outweighed by the reduction in microvascular complications" (DCCT Research Group. NEJM 1993:329:977-986.) Moreover, one should remember that the intensive management group in DCCT included both people on pump and on MDI (multiple daily injections.) Smaller studies on intensive management have segmented pump users from those on MDI, and have shown that the risk of hypoglycemia may be significantly lower with insulin pumps [Bode B, Steed D, Davidson P. Diabetes 1994;43 (Supp. 1):220A].
In any case, one must remember that an episode of hypoglycemia does not simply materialize out of thin air, like Barbara Eden coming out of her bottle. Rather, there are definite signs and physiological events that foreshadow its arrival. Clearly, having a sound understanding of the causes of hypoglycemia, and the means for preventing its occurrence, should be a priority for everyone in today's post-DCCT environment.
Hypoglycemia IS, Hypoglycemia DOES
The body normally has a number of mechanisms that prevent the onset of hypoglycemia, not the least of which is the ability to produce the right amount of insulin in response to the body's blood glucose levels. Beta cells in the pancreas are continuously "testing" blood glucose, and if the level falls too much, they slow their secretion of insulin accordingly. If blood glucose levels continue to fall, the beta cells stop releasing insulin and the body mounts several lines of defense to prevent a further decrease. First, the alpha cells in the pancreas begin to secrete glucagon, a hormone which raises blood glucose levels. If glucagon fails to get the job done, the adrenal glands secrete another hormone called epinephrine. Sometimes referred to as the "fight or flight" hormone, epinephrine stimulates the liver to convert stored glycogen into glucose. In addition, epinephrine provokes sweating, tingling, a racing heartbeat, and a general sense of nervousness: all of the telltale warning signs of hypoglycemia. Taken together, the mechanisms which control insulin, glucagon and epinephrine secretion provide a major barrier to the onset of a hypoglycemia episode.
Life in the modern world is replete with distractions, and unfortunately these can sometimes cause the symptoms of impending hypoglycemia to go unnoticed. The noisy children, demanding boss, and a host of daily concerns can cause us to "tune out" what our bodies are trying to tell us.
More insidious, however, is a phenomenon which can affect people who have had diabetes for a long time or who have experienced multiple bouts of hypoglycemia. Known as "hypoglycemia unawareness," this is a syndrome in which the normal warning signs of hypoglycemia fail to appear. When Type I diabetes develops, insulin secretion is soon lost as a defense mechanism. More importantly, as time passes the pancreatic alpha cells and the adrenal glands can become desensitized and lose their ability to secrete glucagon and epinephrine in response to hypoglycemia. Not only does the body lose its biochemical tools for fighting of hypoglycemia, it also fails to provide the physiological warning signs that an episode is imminent: the pounding heartbeat, the dizziness, the sweaty palms, etc. As a result, there is even less time to take corrective action such as ingesting carbohydrates.
Some people who have diabetes may lose these early warning systems as time passes. Most people with diabetes lose their glucagon response within the first few years, for reasons that have not been fully elucidated. One theory says that the glucagon producing alpha cells are damaged by the same process that destroys insulin producing beta cells. People who have had diabetes for a long time may lose the epinephrine response as well, perhaps related to autonomic nerve impairment (due to neuropathy). Therefore, anyone who has had Type I diabetes for several years is at potential risk for hypoglycemia without warning.
