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Insulin Use and Exercise, Part 1: Faster and Intermediate-Acting Insulins

Mar 31, 2009
 

When you don’t have diabetes and you start any activity, your body increases the release of glucose-raising hormones to prevent falls in your blood glucose levels. At the same time, your pancreas releases less insulin during exercise. But what about your patients who have diabetes? Sheri Colberg, Ph.D., FACSM, discusses how you can help your patients in this week’s feature

Insulin Use and Exercise, Part 1: Faster and Intermediate-Acting Insulins

 

By Sheri Colberg, Ph.D., FACSM

SheriAt the start of any activity, your body increases the release of glucose-raising hormones to prevent falls in your blood glucose levels. At the same time, your pancreas releases less insulin (if you still make any) during exercise. But if you have to depend on insulin by injections or pump or if you use certain other medications, your body may not be able to respond normally. You can’t turn off insulin from an injection site, and exercise can sometimes speed up its absorption by increasing blood flow to your muscles and skin. As a result, instead of having less insulin circulating around your bloodstream during exercise, you may end up with more than normal, which can easily lower your blood sugars too much. Similarly, certain oral diabetic medicines can also augment the effects of insulin during exercise or cause greater release, also potentially resulting in hypoglycemia.

Insulin Use: Effect on Spontaneity and More

Have you ever felt like jumping on your bike and going for a ride without giving any thought to where you’re going or how long you’ll be gone? When you have diabetes and you use insulin, the problem with such spontaneity is that your insulin levels during an activity can greatly affect your blood sugar response to exercise (refer to figure 2.6 in chapter 2). To predict your response to a workout, you must take into account what types of insulin you use, when you last took any, and how much is in your bloodstream before, during, and afterward.

Different insulins have varying times to peak action and unique durations, both of which can make activities (especially spontaneous ones) harder to handle. Several types of insulins are now on the market, further complicating matters. In general, insulins are considered rapid- or short-acting, intermediate-acting, or long-acting depending on their onset, peak, and duration. Each type of insulin potentially has a different effect on your blood sugar responses to exercise. A fact of life for insulin users is that spontaneity must usually be moderated with extra carbohydrate or immediate insulin changes to prevent hypoglycemia.

Key Point: Knowing when your insulins peak is crucial to determining your blood sugar responses to exercise and your need for extra carbohydrate or lower insulin doses.

Short- and Rapid-Acting Insulins: Good for Covering Carbohydrate Intake

As for the shorter-acting insulins, human-synthetic regular insulin (most common trade names: Humulin R, Novolin R, and Actrapid) is still available, but few manufacturers make beef and pork combinations anymore. Insulins of synthetic origin that have the same structure as human ones generally have faster onset, quicker peak time, and shorter duration than their previous animal counterparts and are less likely to cause allergic reactions.

In just the past decade, several rapid-acting insulins have hit (and taken over) the market from regular insulin, including Humalog (generic name: lispro), NovoLog or NovoRapid (aspart), Apidra (glulisine), and VIAject, an extremely rapid-acting formulation that is absorbed in about half the time as Humalog. These products are actually insulin analogs; they have a structure similar to that of insulin, but the order of the amino acids (i.e., protein building blocks) is slightly modified, which results in faster absorption and shorter duration. The benefit of these analogs for regular exercisers is that they’re mostly gone from your circulation within two hours after you take them, lowering your risk of getting low when active later. Most insulin pump users are now using one of these rapid-acting analogs in their pumps for both basal and bolus insulin coverage. For a comparison of the onset, peak, and duration of these and other currently available insulins, refer to table 3.1.

Table 3.1: Human Insulin Action Times

Insulin

Onset

Peak

Duration

Humalog, NovoLog, and Apidra

10–30 minutes

0.5–1.5 hours

3–5 hours

Regular (R)

30–60 minutes

2–5 hours

5–8 hours

NPH (N), Protophane

1–2 hours

2–12 hours

14–24 hours

Lantus

1.5 hours

None

20–24 hours

Levemir

1–3 hours

8–10 hours

Up to 24 hours

Note: Individual action times may vary depending on environmental conditions, activity level, injection site, and dosage taken.

Early in the new millennium, an inhaled insulin called Exubera also received approval for use in the United States. Just recently though, the manufacturer decided to stop making it because of lackluster sales. Its onset was similar to the rapid-acting insulin analogs, but its duration was more like regular insulin. Although other companies are working on perfecting the delivery of insulin through inhalation or by mouth (orally), the only insulins currently on the market are still the ones that you have to inject with a syringe or infuse with a pump.

 Intermediate-Acting Insulins: Not as Widely Used Anymore

Some intermediate-acting insulins are available as well. NPH (trade names: Humulin or Novolin N in the United States and Protophane elsewhere; generic name: isophane) is the most common insulin of this type. Although others are available, they all generally have the same or similar actions as NPH in terms of their onset, peak action, and duration. A usual regimen is NPH at breakfast along with regular or Humalog to cover breakfast, an optional rapid-acting injection at lunch, a mandatory one at dinner, and another dose of NPH at bedtime. An alternative regimen is to take rapid-acting insulin doses during the day with a single bedtime dose of NPH. If you have Type 2 diabetes, you may be using NPH alone (usually at bedtime) or a mixture of NPH and a shorter-acting one (e.g., a 70–30 mix or another mix).

In my next column (Part 2 on insulin use), we will talk more about use of basal insulin and insulin pumps.

This column is excerpted from Diabetic Athlete’s Handbook (released November 2008 from Human Kinetics), which contains essential exercise-related information and examples for Type 1 and Type 2 diabetic exercisers. Look for it in stores or find links to places to buy it online on www.shericolberg.com, along with additional information.

Courtesy of www.diabetesincontrol.com