Insulin Use and Exercise, Part 2: Longer-Acting, Basal Insulins
By Sheri Colberg, Ph.D., FACSM
In Part 1, we discussed use of rapid- and short-acting insulins, as well as intermediate-acting ones. In this column, the use of longer-acting, basal insulins is covered.
Basal Insulins and Basal-Bolus Regimens
Two relatively new basal insulins, Lantus (generic name: glargine) and Levemir (detemir), are now available and have replaced the use of other long-lasting insulins like Ultralente. The main difference between these two newer insulins is that Lantus lasts up to 24 hours and is usually taken once daily, and Levemir requires twice-daily dosing. Both are supposed to be peakless and provide coverage for your basal insulin needs, but you’ll likely have to use rapid-acting insulin to cover your meals and snacks effectively if you don’t make enough of your own.
The benefit of either of these basal choices is that you can effectively replace just your basal insulin needs and cover meals and snacks solely with rapid- or short-acting insulins. The downside is that basal insulins last 12 to 24 hours, making it harder to implement short-term corrections in basal insulin coverage for unusual or prolonged activities unless you purposefully lower your doses in advance. Also, as mentioned, absorption can be inconsistent because of your choice of injection site, activity level, massaging the area, hot tubbing, or other factors that may speed up how quickly it shows up in your circulation, resulting in basal insulin levels that are first too high and later too low.
Many diabetic athletes have very low basal insulin needs, a scenario that presents a problem when it comes to using Lantus once a day. If you take less than 20 units a day, your basal coverage is unlikely to last a full 24 hours as promised. (Actually, if you read the package insert, you’ll see that the duration is quite variable and as short as 12 hours for some people.) In general, with all insulin, even basal ones, the smaller the dose you take, the more rapidly it is absorbed because of the surface area of the insulin depot (the spot where the insulin is injected) under your skin.
Key Point: For many Lantus users who only need small doses of insulin, coverage lasts significantly less than 24 hours, which may make twice-a-day dosing more effective for basal coverage.
The athletes who have mentioned this problem have found its maximal duration to be about 16 to 22 hours. One way to get around this problem is to give Lantus like Levemirâ€”split into doses that you give twice a day instead of only onceâ€”which is what a lot of small-dose Lantus users actually do. Dr. Karen Stark of Saint Louis Park, Minnesota, compared these two basal insulins on herself and found that she has to be more cognizant of taking Levemir at the same time every day because its duration is definitely shorter. On the flip side, she noticed that Lantus has more of a peak than Levemir and that she’s likely to experience Lantus-induced lows in the first 6 to 12 hours after taking it, whereas Levemir is absorbed more evenly with less chance of peaking and causing low blood sugars.
A recent study also demonstrated that blood glucose levels in anyone using Lantus usually rise around the time that you’re supposed to give your next dose (whether you give it at bedtime, dinner, or lunch). Bedtime injections in particular lead to hyperglycemia in the early part of the night, which is improved if you give your single dose at lunch or dinner instead. Regardless of when you give it, keep in mind that you may need to take extra rapid-acting insulin to cover the rise in your blood sugars when your Lantus dose wears off.
In Part 3 of this series, the use and features of insulin pumps will be covered.
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.