NIDDM (non-insulin dependent diabetes mellitus) is by far the most common form of diabetes, accounting for about 90% of all sufferers. The proportion of people affected by this condition climbs in each age group, reaching 18% in 64- to 75-year-olds and as many as 40% in those over 80. Moreover, it has been estimated that for every known elderly diabetic another remains undiagnosed. All face a greatly increased risk of arterial problems leading to coronary heart disease, stroke and circulatory dysfunction, as well as the known eye, kidney and nervous system complications of the disease, which can cause impaired vision or blindness, foot ulcers or amputations.
What is non-insulin dependent diabetes mellitus?
Usually NIDDM is the combination of two problems: firstly, the failure of patients to secrete enough glucose, and secondly, insulin resistance, or the reduced efficiency of insulin owing to a failure by the body’s tissues to respond to it as they should. Although people with non-insulin dependent diabetes mellitus all have some degree of insulin deficiency in the pancreas, they often have quite high levels of insulin in the blood. Their problem is that becuase of insulin resistance, even those fairly large amounts of insulin are not enough to control their glucose levels.
Large injected doses of insulin can overcome insulin resistance and increase the uptake of glucose by skeletal muscle, but prolonged heavy use of insulin tends to increase body weight and may also increase the risk of cardiovascular disease. Perhaps most importantly, it greatly increases the risk of hypoglycemic episodes (glucose deficiency) – particularly serious in elderly patients who are weaker and may have underlying heart problems. Therefore, the goal in treating elderly patients with non-insulin dependent diabetes mellitus should be to control glycemic levels with the minimum possible amount of insulin.
Why target the liver?
Fortunately, while it takes a lot of insulin to increase glucose uptake, it takes a lot less to decrease glucose production by the liver. Because of this, a single bedtime injection can give similar results in terms of glycemic control to a daytime administration, but with smaller doses and therefore reduced side effects. In general, doctors should be more tolerant of glucose levels in older patients because their kidneys have a higher threshold of tolerance for glucose, and because trying too strictly to maintain glycemic levels at optimum produces fewer benefits and greater risks for older patients.
Studies of the effect of intensive insulin therapy on elderly patients have shown that while a single evening dose of insulin brought glucose levels down appreciably, an additional two, three, or more injections during the day had little further effect. During follow-up, however, those patients who received intensive insulin treatment experienced a twofold increase in major cardiovascular events compared with patients who received a single dose.
Why use insulin at all?
While such data suggest that large doses of insulin may do more harm than good in elderly patients, it is important to remember that insulin, and insulin alone, can always lower blood glucose levels; it is simply a matter of finding the right dose. Recent studies have shown that poor control of blood glucose is, in the long run, a recipe for increased cardiovascular risk. Today, most doctors feel it is better to intervene to try to improve glycemic control. Innovations such as the insulin pen have made self-injection easier, and self-administration of an evening dose now presents no problem for most elderly patients if they are clearly and patiently taught how to do it.
It is reasonable to set the same goals for insulin therapy for elderly patients as for middle-aged diabetes sufferers. Hyperglycemic symptoms, such as thirst, blurred vision, frequent urination and even coma, can and should be prevented through insulin therapy. Exercise, within the limits of what’s possible for an elderly patient, can cut body mass and improve metabolic control. Finally, bacterial infections and diabetic complications can be reduced, delayed, or prevented. The non-interventionist philosophy of the past did not achieve any of these goals.
Who should receive insulin therapy?
Two considerations are important when evaluating a patient’s likely response to insulin therapy aimed at cutting glucose production. One is that not all non-insulin dependent diabetes mellitus patients have the same metabolism. As a general rule, obese patients are more likely to have higher insulin resistance, whereas leaner patients are more likely to have poor insulin secretion.
Secondly, NIDDM can transmute with time into insulin-dependent diabetes mellitus (IDDM), particularly in women who are not obese and who have a history of other auto-immune diseases. The transition to frank IDDM is often harder to detect in elderly patients, who will require insulin therapy as a matter of course – and the earlier it begins, the better.
In other cases, however, an apparent failure of diet and oral drug therapy, which would seem to indicate the need for insulin therapy, may be traced to an unrelated infection or heart problem which increases insulin resistance. Rather than simply bombarding the patient with insulin, the root of the problem should be addressed. Under certain circumstances, even psychological problems such as depression can cause this kind of fluctuation in glycemic control.
Conclusion
NIDDM remains notoriously difficult to treat in elderly patients. But there is no excuse for inaction, nor should older patients be lumped together in treatment programs more suited to younger patients. There is a way to offer them the benefits of improved glycemic control, without exposing them to the risks of intensive insulin therapy. A single nightly injection of insulin can allow an elderly patient to enjoy a normal day of meals and exercise without undue fear of a disastrous hypoglycemic episode.