Chapter 3

Understanding Diabetes Medications

IN THIS CHAPTER

check Finding out how various diabetes medications lower blood glucose

check Adjusting insulin and other medications for exercise

check Minimizing the exercise effects of other medications

Using prescribed medications to treat diabetes — type 2 in particular — never used to be so complicated. You had one main class of drugs (sulfonylureas), along with insulin, but no other options. Now, multiple classes of medications are available that target tissues from your pancreas to your liver, intestines (gut), and kidneys. Which ones are best to use can be hard to sort out.

In this chapter, you uncover information about these options and how they work. The various insulins may need to be adjusted based on your physical activities, and being regularly active may allow you to lower doses of other medications, too. You also find out more about the effects of some other medications that you may be taking and whether exercise impacts them so you can get the most out of your workouts and get as fit as possible.

Knowing How Oral Diabetes Medications Work

If you have type 2 diabetes and use diabetes medications that you take as a pill by mouth, you benefit by understanding how they may or may not lower your blood glucose during activities. When you get more active, you may need lower doses, even of oral medications that don’t usually cause low blood glucose with exercise.

warning If you have type 1 diabetes, most oral medications won’t manage your blood glucose (except possibly metformin if you’re insulin resistant). However, some people with type 1 diabetes use pills to lose more glucose through urine or other medications to help lower glucose variability and lose weight (but they’re using them off label, which means that they’re not approved by the FDA for use by people with type 1).

Targeting specific tissues

The number of diabetes medications available for persons with type 2 diabetes has skyrocketed recently, with 12 classes of medications now available that target different tissues in your body. The targets now include the pancreas (increasing insulin release), liver (decreasing blood glucose release), muscles (making them more responsive to insulin), gut (slowing down absorption of carbohydrates), and kidneys (releasing excess glucose in urine).

remember Among oral medications, only the ones that target the pancreas and cause insulin release have any significant effect on your exercise blood glucose responses.

technicalstuff Metformin works by targeting the liver to reduce blood glucose release overnight and after meals; it also increases insulin action. Sulfonylureas like Amaryl and Glyburide help stimulate your pancreas to make more insulin (if it can). Both Actos and Avandia, drugs in the thiazolidinedione (TZD) class, sensitize fat and muscle cells to insulin. A newer class of drugs (SGLT-2 inhibitors) acts on the kidneys to cause excess blood glucose to be peed out.

Identifying which pills work best to lower glucose

Some people have elevated blood glucose levels in the morning only, while others experience spikes after eating. Your doctor may prescribe medications for you based on which body tissues are the target (see the preceding section) and add other ones to the mix if your blood glucose isn’t coming down enough. Here’s a breakdown of how each of the following classes of medications works:

  • Sulfonylureas: These medications stimulate your pancreas to release most insulin and have been around the longest to treat type 2 diabetes. They include Amaryl, DiaBeta, Diabinese, Glynase, Glucotrol, Micronase, and others. The newer generation sulfonylureas have fewer bad side effects than the older ones. These medications are generally less expensive than newer types.

    remember If your pancreas loses the capacity to make much insulin, no medication will be able to stimulate your beta cells to make enough to manage your blood glucose.

  • Biguanides (metformin): Metformin is the generic name of the only medication in this class. It’s one of the most widely prescribed medications for type 2 diabetes and prediabetes (and other insulin-resistant states) and the drug of first choice for these conditions. It doesn’t cause hypoglycemia, but it can shut down your liver’s release of glucose overnight, making it excellent for preventing morning elevations. It also improves the action of your insulin in both the liver and muscles.
  • Thiazolidinediones (TZDs): These medications act as insulin sensitizers to boost insulin action. Two medications in this class, Avandia and Actos, are available. They can increase bone fractures and swelling of the feet and ankles, and you can’t take them if you have heart failure. Both may cause you to gain weight.
  • DPP-4 inhibitors: DPP-4 inhibitors work with gut hormones, natural enzymes, and your body’s own insulin to lower blood glucose. They may help preserve the ability of the beta cells of the pancreas to make insulin.

    technicalstuff Incretin hormones, called GLP-1 and GIP, are naturally occurring substances produced in the intestines when you eat, and they help regulate blood glucose by stimulating both the alpha and beta cells of the pancreas. Alpha cells secrete glucagon, which mobilizes glucose when your blood glucose is low (such as overnight or during prolonged activity). These medications boost the incretin response by inhibiting DPP-4, an enzyme that breaks down incretin hormones before they have time to work effectively.

  • Meglitinides: Prandin and Starlix are the two drugs in this class, which may work well for you if you eat sporadically. You take a dose when you eat to cause your pancreas to release enough insulin then to reduce blood glucose spikes after meals. They are one of the oral medications sometimes prescribed for women who have gestational diabetes (during pregnancy).

    tip If your blood glucose rises sharply after you eat, you can benefit from these medications, assuming your beta cells can still release enough insulin.

  • Alpha-glucosidase inhibitors: These medications control your post-meal spikes by slowing how quickly you digest carbohydrates after eating. You can dose with either Precose or Glyset, the two medications in this class, but only if you don’t have slowing of your digestion caused by gastroparesis (central nerve damage). This medication is also an option for women who are pregnant and have gestational or type 2 diabetes.
  • SGLT-2 inhibitors: This more recent class of medications treats diabetes by making you lose glucose through your urine. Because more glucose appears in the urine, taking these medications raises your risk of yeast infections slightly, especially in women, as well as of urinary tract (bladder) infections and dehydration. These medications have been associated with ketoacidosis (elevated levels of ketones in the blood) in both individuals with type 1 and type 2 diabetes even with only moderate elevations in blood glucose.

    technicalstuff Around 160 to 180 grams of glucose a day are filtered through the kidneys, but they don’t appear in urine because they’re reabsorbed back into your bloodstream. When your blood glucose rises above 180 mg/dL, however, some glucose normally ends up in your urine. These SGLT-2 (sodium-glucose co-transporter-2) inhibitors block glucose reabsorption and cause you to lose some glucose and calories in urine and usually lose some weight.

Even if you start out taking only one medication, ending up being prescribed two or more is common. Combination drugs that have two of these drugs in one pill are popular for that reason. For instance, Glucovance and Metaglip combine a sulfonylurea and a biguanide, and Avandamet is a combination of a glitazone and a biguanide. Combinations of some of the newer medications (like DPP-4 and SGLT-2 inhibitors together in Glyxambi, a combination of Tradjenta and Jardiance) are now available. Expect many new combination diabetes pills to be available in the future, reducing the number of pills you may take on a daily basis.

tip Table 3-1 provides a handy summary of the various types of oral diabetes medications currently available.

TABLE 3-1 Oral Diabetes Medications

Class of Medication

What They’re Called

How They Work

Sulfonylureas

Amaryl, DiaBeta, Diabinese, Glynase, Glucotrol, Micronase

Promote insulin release from the beta cells of the pancreas; some increase insulin action

Biguanides

Metformin (generic), Glucophage, Glucophage XR, Riomet, Glumetza

Decrease glucose release from the liver; increase liver and muscle insulin sensitivity

Thiazolidenediones or glitazones

Avandia, Actos

Increase insulin sensitivity in muscles

DPP-4 inhibitors

Januvia, Onglyza, Nesina/Galvus, Tradjenta

Inhibit DPP-4 that breaks down GLP-1; improve insulin action, lower glucagon

Meglitinides

Prandin, Starlix

Stimulate beta cells to release insulin, but only enough to cover meals

Alpha-glucosidase inhibitors

Precose, Glyset

Work in gut to slow carbohydrate digestion and lower post-meal blood glucose spikes

SGLT-2 inhibitors

Invokana, Farxiga, Jardiance, Steglatro

Prevent kidneys from reabsorbing glucose; lost in urine when above a certain level

Combination therapies

Glucovance, Metaglip, Avandamet, Avandaryl, Duetact, Glyxambi

Combine effects of two medication classes in each pill

Using (Non-Insulin) Injected Medication

You can use other medications besides insulin that are injected and treat type 1 and type 2 diabetes. One class (amylin) replaces a hormone secreted with insulin, and the other (GLP-1 agonists) affects the gut hormones. Table 3-2 summarizes these two classes quickly, and the following sections provide more detail.

TABLE 3-2 Injected (Non-Insulin) Diabetes Medications

Class of Medication

What They’re Called

How They Work

Amylin

Symlin

Work with insulin to control glucose spikes for three hours after meals

GLP-1 agonists (incretins and incretin mimetics)

Byetta, Victoza, Lyxumia, Bydureon, Trulicity, Ozempic, Eperzan, Adlyxin

Stimulate insulin release; inhibit the liver’s release of glucose; delay emptying of stomach

Amylin

If your body makes very little or no insulin, you’re missing a hormone called amylin. A replacement form, Symlin (pramlintide), can be injected by people with type 1 diabetes or anyone with type 2 using insulin. Symlin works with insulin after meals to slow the glucose coming into the blood from digested foods. It can help you lose weight by making you feel full sooner, as well as improve your diabetes management and lower the risk of complications.

Symlin has some potential side effects, including severe hypoglycemia (low blood glucose, mostly in type 1s), nausea, vomiting, abdominal pain, headache, fatigue, and dizziness. Another drawback is that it can only be injected, not taken by mouth. If you have diabetes-related digestive problems (gastroparesis), you shouldn’t use this medication.

GLP-1 agonists

People with type 2 diabetes can also use a class of injected medications known as glucagon-like peptide-1 agonists, or GLP-1 agonists. These medications delay digestion and cause you to feel full sooner and possibly lose weight.

technicalstuff GLP-1 agonists replicate a synthetic version of a small protein derived from the venom of the Gila monster (a poisonous lizard found in the southwestern United States and in Mexico). These gut hormones stimulate the release of insulin when you eat. They also protect your pancreatic beta cells from burnout, inhibit the liver’s release of glucose (by blocking glucagon), delay the emptying of food from your stomach, and promote early fullness.

Despite occasional side effects such as nausea, vomiting, temporary headaches, and increased risk of blood glucose lows when used with sulfonylureas or insulin, replacement of these natural hormones can treat type 2 diabetes quite effectively. A drawback for many potential users, though, is that some types must be injected daily (Byetta and Victoza), although once-weekly forms (Bydureon, Trulicity, and Ozempic) are available.

Changing Doses for Exercise

The medications you take to manage diabetes or other health conditions can alter your blood glucose responses to being active. If you take certain pills or insulin, you must be vigilant about adjusting how much you take and what you eat to avoid ending up with blood glucose that is too low or too high from exercise.

If you take medications that increase the secretion of insulin, or if you take insulin, you have a greater risk of exercise-induced blood glucose lows. To prevent hypoglycemia, you may have to adjust other medications for regular exercise or lower your insulin doses before and possibly after your workouts. (The earlier sections in this chapter explain the basics of the various classes of diabetes medications.)

Oral medications that may cause exercise lows

Most oral medications are unlikely to cause lows, with a few exceptions. Any pills that cause your pancreas to release insulin increase your risk of hypoglycemia with exercise. For the sulfonylureas, the actual risk varies with how long the medication works. For the meglitinides, the timing of when you take the pill before exercise matters.

Sulfonylureas

Sulfonylureas are one class of medications with definite potential effects on exercise, increasing the risk for hypoglycemia in people with type 2 diabetes. Older-generation sulfonylureas (such as Diabinese, Orinase, Tolinase, and Dymelor) cause insulin to be released from the pancreas and reduce insulin resistance. These typically have a longer duration (up to 72 hours) than the newer ones, creating the greatest potential for lows during and after exercise.

Second-generation sulfonylureas, such as Amaryl, DiaBeta, Micronase, and Glucotrol, don’t last as long and carry a lesser risk. DiaBeta and Micronase have a slightly longer duration (24 hours) versus 12 to 16 hours for Amaryl and Glucotrol.

tip Keep these guidelines in mind if you use any of these medications:

  • Frequently monitor your blood glucose levels when exercising if you take any sulfonylureas that stay in your body for 24 hours or longer.
  • Choose to take Amaryl and Glucotrol if you want a reduced chance of getting low during or after exercise because their effects don’t last as long.
  • Check with your health care provider about lowering your doses of sulfonylureas, particularly if you begin to have lows more frequently.

Meglitinides

Prandin or Starlix only potentially increase your risk of low blood glucose if you take them immediately before prolonged exercise because they increase insulin levels in the blood temporarily when taken with meals.

warning However, if you take Prandin or Starlix before meals after which you plan to exercise, you may need to lower your doses to avoid hypoglycemia.

Medications unlikely to cause lows

Other diabetes medications may affect exercise even less or not at all. The following list and Table 3-3 spell out some of their other possible effects so you can be informed before you get active.

  • Insulin sensitizers: Medications that increase insulin sensitivity (Avandia, Actos, and metformin) only affect it when you’re resting. They don’t cause exercise lows.
  • Alpha-glucosidase inhibitors: The slower absorption of carbohydrates Precose and Glyset cause doesn’t directly affect exercise blood glucose levels. However, these medications can slightly delay your treatment of a low blood glucose level during workouts.
  • DPP-4 inhibitors: During low blood glucose, people taking these medications have a greater release of glucagon, which helps raise glucose levels. They don’t cause lows.
  • SGLT-2 inhibitors: These medications have no known exercise effects, even though they may lower blood pressure by causing you to pee out extra water when your blood glucose goes high. To be on the safe side, drink plenty of fluids to stay hydrated.

TABLE 3-3 Oral Diabetes Medications and Risk of Exercise Lows

Class of Medication

Specific Medications

Risk of Exercise Lows

Sulfonylureas

Diabinese, Glynase, Orinase

High (last > 24 hours)

DiaBeta, Micronase

Medium-high (24 hours)

Amaryl, Glucotrol

Medium (12 to 16 hours)

Biguanides

All formulations

Low

Thiazolidenediones

Avandia, Actos

Low

DPP-4 inhibitors

Januvia, Onglyza, Nesina, Tradjenta

Low

Meglitinides

Prandin, Starlix

Moderate (during exercise after meals)

Alpha-glucosidase inhibitors

Precose, Glyset

Low

SGLT-2 inhibitors

Invokana, Farxiga, Jardiance, Steglatro

Low

Injected (non-insulin) medications

None of the non-insulin, injectable medications impact glucose responses to exercise unless you take them with insulin or you have slower digestion from diabetes. Problems may arise if your blood glucose drops for other reasons.

By slowing how quickly carbohydrates are digested, these medications make exercise lows harder to treat. This difficulty can occur with use of either Symlin that you inject for meals or GLP-1 agonists that you inject daily or weekly.

warning If you use Symlin and try to treat a low, your body will digest the carbohydrates you take more slowly, making raising your blood glucose quickly more difficult.

warning Some individuals with type 2 diabetes find that long bouts of exercise are much more difficult to accomplish when using GLP-1 agonists because they feel more sluggish and less able to do their fitness routines.

Check out Table 3-4 for a handy summary of the risk of exercise lows with injected diabetes medications.

TABLE 3-4 Injected Medications and Risk of Exercise Lows

Class of Medication

Examples

Risk of Exercise Lows

Insulin (bolus: injected or pumped)

Humalog, NovoLog, Apidra, Fiasp, Regular (R)

High (given within 2-3 hours of last bolus)

Insulin (basal: injected, not pumped)

Lantus, Basaglar, Levemir, Toujeo, Tresiba, Novolin N, Humulin N

Moderate (but lower overall doses may be needed when active)

Amylin

Symlin

Low (can make hypoglycemia harder to treat effectively)

GLP-1 agonists

Byetta, Victoza, Lyxumia, Bydureon, Trulicity, Ozempic, Eperzan, Adlyxin

Low

Understanding Insulin Use

All people with type 1 diabetes and many with type 2 must give themselves insulin to manage blood glucose, whether that insulin is injected, pumped, or inhaled. (In the future, a swallowed form may be an option.)

remember If your blood glucose is high (greater than 250 mg/dL) at diagnosis, your doctor may start you on insulin right away, regardless of your diabetes type.

Taking insulin allows you to rapidly achieve better blood glucose and may give your beta cells a rest so they can recover at least some of their function. Being put on insulin with type 2 diabetes isn’t a sign that you have failed or that your diabetes is worse. In fact, when people with type 2 diabetes are started on insulin early, they’re unlikely to need to take it a year later (although they may need it years down the road).

If you have type 2 diabetes, your insulin doses may be decreased or withdrawn if lifestyle changes (improvements in food, diet, stress management, and more) can manage your blood glucose. That period of improved blood glucose when you start using insulin also has a lasting effect in terms of preventing diabetes complications for both types.

Often when adults develop type 1 diabetes, their insulin needs are low for several years and result in a misdiagnosis of type 2. Most individuals with type 1, however, require insulin from diagnosis on, and oral medications don’t effectively lower blood glucose.

Basal and bolus insulins and their actions

Insulins have been formulated to act differently. Depending on the type, they lower glucose at different times after you take them (onset), reach maximal concentrations in the blood (peak) at varying times, and last for shorter or longer times in the body (duration).

Most people with type 1 diabetes follow a basal-bolus regimen, meaning that they take basal (longer-lasting, or background) insulin to cover their needs all day long and bolus (shorter-acting) insulin to cover increases in blood glucose from meals and snacks. See Table 3-5 for more about the actions of the various insulins. You can follow this regimen whether you inject or pump insulin. In the case of pumps, they are unique in that they use shorter-acting insulins only but are programmed to deliver doses over time that cover basal insulin needs. People using them have a separate program in the pump to give bolus dose for meals and snacks.

TABLE 3-5 Characteristics of Insulins and Insulin Analogs

Insulin/Insulin Analog

Onset

Peak

Duration

Fiasp

2–15 minutes

0.25–2.0 hours

2–5 hours

Humalog, NovoLog, Apidra, Admelog

10–30 minutes

0.5–3.0 hours

3–5 hours

Regular (R)

30–60 minutes

2–5 hours

5–8 hours

N (NPH)

1–2 hours

2–12 hours

14–24 hours

Lantus, Basaglar, Toujeo

1.5 hours

None

20–24 hours

Levemir

1–3 hours

8–10 hours

Up to 24 hours

Tresiba

30–90 minutes

None

Over 24 hours

remember If you have type 2 diabetes and need to take insulin, your doctor may first put you on only basal insulin, which covers your non–food-related insulin needs and provides stable amounts of insulin during the day.

Basal insulins

At present, the most widely used basal insulins are Lantus, Basaglar, and Levemir, all of which you can inject once or twice a day. Note: For many Lantus/Basaglar users who need small total daily doses of basal insulin, their insulin lasts significantly less than 24 hours, and they may need to take it twice a day.

remember Basal insulins don’t directly cover the carbohydrates you eat during the day, but they help you start the day with better glucose readings. They also maintain your blood glucose throughout the day by covering your body’s insulin needs that remain the same regardless of whether you eat.

An even longer-acting one called Tresiba covers your basal insulin needs for well over 24 hours. In addition, the manufacturers of Lantus recently created a version of basal insulin called Toujeo at three times the strength per volume (especially made for people who take large doses of basal insulin).

Combination basal and bolus insulins (intermediate-acting)

Intermediate-action insulins like Humulin N can cover both basal needs and some meals (like lunch, which is when it peaks if given before breakfast), but they’ve become less popular than longer-acting basal insulins that better mimic the normal release of insulin. People with type 2 diabetes may also be put on combination insulins, such as 70/30 or 75/25, containing more basal or intermediate insulin (70 or 75 percent) with less of a rapid-acting one (the other 25 or 30 percent) to cover meals. Using premixed insulin may increase the risk of hypoglycemia.

For many with type 2 diabetes, using combination insulins is effective. Premixed formulations may make taking the proper combination of insulin to best cover all your body’s daily needs easier, although these options aren’t as effective for people who make none of their own insulin (that is, those with type 1 diabetes).

Bolus (mealtime) insulins

The main rapid-acting insulin analogs (all synthesized and slightly altered forms of human insulin) you can use are Humalog, NovoLog (or NovoRapid), Admelog, and Apidra. Their differences in onset and peak times are minimal, but all work more rapidly than regular (for example, Humulin R) insulin. Another one, Fiasp, just gained FDA approval and is even more rapid-acting than all of these insulins, with a quicker onset and 50% more insulin delivered during the first hour after you inject it. You can use any of these to cover food at meals or to correct high blood glucose, and usually one is used in insulin pumps.

Insulin delivery methods

You have many options to choose from on how to take insulin, such as syringes (of varying needle length and dosing scales), insulin pens, insulin pumps, or inhaled insulin, with other possibilities likely coming down the pike soon. The following sections outline some of these choices.

Syringes and pens

You can use syringes or choose insulin pens that contain prefilled insulin cartridges. Using insulin pens reduces the chances of giving yourself a dose of the wrong insulin when you use more than one type because each insulin has its own unique injection pen. Giving an exact dose dialed on a pen is also easier than filling a syringe from an insulin vial to the correct amount (which can be particularly difficult if you can’t see well).

tip If you take insulin, ask your doctor whether an insulin pen would be better for you than syringes. Several pens now have memory functions (recording the last dose and time), and some have half-unit dosing rather than just whole units.

remember For all injected insulins, smaller doses are generally absorbed from your skin and available in your bloodstream more rapidly than larger ones, but smaller doses also have a shorter duration.

Insulin pumps

You may take insulin by using a specialized insulin pump, which is usually about the size of a pager or small cellphone (or smaller). Pumps use a small catheter or needle under your skin to frequently deliver basal doses of short- or rapid-acting insulin to mimic normal insulin release by the pancreas. You program the pump to give yourself boluses to cover your meals and snacks.

remember In other words, pumps provide insulin more like your own pancreas would: in small doses all day long, with bigger doses following eating.

You can closely mimic this same pattern with the newer basal/bolus regimens (for example, Lantus insulin for basal, Humalog for boluses), but insulin pumps make insulin delivery easier and are flexible enough to allow you to change basal rates of insulin delivery at any time or put in a temporary basal rate for exercise or anything else that changes your insulin needs.

remember Using an insulin pump requires having an understanding of the impact of your food and doing frequent blood glucose monitoring (just like if you take multiple daily injections). But you only have one needle stick when the infusion set is inserted every three to five days. The insulin is directly infused into the skin through the same catheter, which stays under your skin.

technicalstuff Insulin pumps have been available since the 1980s. You now have several models from which to choose. Most still require tubing to deliver insulin from the pump through the infusion site below the skin, but several tubeless patch pumps are now available. On most pumps, the built-in features routinely include a bolus calculator that helps to determine how much insulin to give for food and correction, along with a dual wave or square wave to change the duration of the bolus delivery itself. The “active insulin” feature for the insulin still available in the system can help prevent stacking (that is, giving doses too close together). By checking blood glucose frequently after a bolus to see when levels stop falling, you can figure out how long it lasts.

Inhaled insulin

One inhaled insulin, Afrezza, is another option for administering rapid-acting insulin for meals. It makes insulin available sooner but doesn’t last as long compared to other rapid-acting insulins. One issue with its use is that the possible doses are only four or eight units at a time. Also, it can cause a cough and throat pain or irritation, and smokers or people with asthma or lung problems like emphysema can’t use it.

Insulin and exercise interactions

Using insulin creates the most problems when you’re being active. Insulin is the only hormone that lowers blood glucose. The body normally decreases insulin release during exercise, but when people inject or pump insulin that is absorbed slowly, lowering insulin levels during activities is harder, and hypoglycemia can result.

warning If you take insulin, exercise can cause dramatic reductions in blood glucose.

Here are critical points that you need to understand about taking insulin and balancing your blood glucose during and after exercise:

  • Insulin and contractions use separate mechanisms to take up glucose from the blood, and they additively increase what’s going into muscles.
  • The type of insulin you use and its timing (peak, onset, and duration) can have a large effect on your blood glucose responses.
  • When no more than basal levels of insulin are circulating in your body during exercise, your body’s response is more normal.
  • If you exercise when your insulin levels are peaking, you have an increased chance of getting low.
  • If you use basal insulin only, or your last bolus insulin dose has peaked and waned before you start exercising (usually within two to three hours), your risk of developing hypoglycemia will be much lower.
  • Insulin pump users can prevent lows by either disconnecting their pumps or reducing their basal rates during activity.
  • Some pump users decrease their basal rates before and/or after the activity, depending on how long it lasts and on blood glucose responses.
  • Taking twice-daily doses of basal insulin gives you a greater ability to adjust dosing to prevent hypoglycemia before and after exercise.
  • Exercise, as well as hot tub use and vigorous massage, can increase the absorption of insulin and cause hypoglycemia.

Lowering insulin for physical activity

Physical activity is one of the main causes of hypoglycemia when you use insulin. Knowing when and how to adjust your insulin doses can be critically important to managing your blood glucose. How much insulin is in your bloodstream when you exercise determines much of your response.

remember Exercising with low levels of insulin in your blood is a much more normal physiological response.

warning If your insulin levels are high during an activity, your muscles will take up even more blood glucose, and you’re more likely to end up with low blood glucose for up to 48 hours after you’re done exercising.

Being able to adjust your insulin doses takes a higher level of knowledge about how insulins work, experience adjusting doses, and quite a bit of trial and error, no matter how much you know about your own body’s responses. If you’re unsure about how to adjust insulin doses, consult with your health care provider, particularly if you begin to experience lows related to your activities and are relatively new to being active. Alternatively, you may be able to gauge how to lower pre-exercise insulin doses or increase carbohydrate intake yourself by determining the effects of the activity.

To lower your insulin during exercise, you may need to decrease your insulin doses before meals, as shown in Table 3-6. The general recommendations for insulin adjustments that follow apply to bolus insulins given within two to three hours of when you start to exercise only.

TABLE 3-6 Reduction of Mealtime Insulin Taken Before Exercise

Duration

Low Intensity

Moderate Intensity

High Intensity

30 minutes

None

10–20%

10–30%

60 minutes

10–20%

20–40%

30–60%

90 minutes

15–30%

30–55%

45–75%

120 minutes

20–40%

40–70%

60–90%

180 minutes

30–60%

60–90%

75–100%

Adapted from Colberg, S., Diabetic Athlete’s Handbook (Human Kinetics, 2009).

Consider these general guidelines related to making insulin adjustments to manage your blood glucose during exercise:

  • These recommendations only give you a starting point for making insulin changes; you need to do some trial and error to find what works for you.
  • If you eat extra for exercise, your insulin adjustments may be less, or you may need to both lower insulin and eat more for longer activities.
  • Reduce your carbohydrate intake at meals before exercise to allow you to take smaller doses of insulin (to keep insulin lower during exercise).
  • Larger insulin doses take longer to fully absorb, so they stick around in your body longer and can cause lows later on.
  • Basal rate reductions on pumps may be more or less than recommended for boluses, and they may be done alone or with reduced boluses.
  • You may need to reduce insulin less when exercising more than three hours after your last dose (injected or pumped) of bolus insulin.
  • For the meal after exercise, you may need to reduce bolus insulin doses (such as cutting back by a unit or two).
  • You may also need to lower doses after exercise (bolus and basal), both in the short run and longer term (if your training is consistent).
  • If your activities are seasonal, you may have to lower your insulin doses during the season and raise them again during the off-season.
  • When doing intense, near-maximal exercise, you may need to increase your bolus insulin rather than lower it.
  • Competitions usually have more of a glucose-raising effect (especially when you’re nervous) compared to practices, which usually lower blood glucose.
  • If you use a pump and disconnect it during exercise, check your blood glucose once per hour, reconnect and correct with dosing suggested by the insulin pump (usually at least half of what you missed per hour off the pump).
  • If you use Lantus or Basaglar as your basal insulin and take small doses, you may want to split it into two daily doses. You can then give less to cover the hours during which you’ll be exercising or a smaller dose for the 12 hours following prolonged activities.
  • If you’re ever in doubt about how to adjust your own insulin, check with your health care provider for recommended changes and further guidance.

tip For additional guidance, consult specific activity recommendations in my book Diabetic Athlete’s Handbook (published by Human Kinetics).

Exercise and insulin needs in athletes

As I note in Chapter 2, regular physical training increases your muscle mass, in effect giving you a larger glucose tank in which to put excess glucose after meals. What you may not know is that trained athletes generally have low levels of circulating insulin for this reason and are extremely insulin sensitive. Insulin action, though, begins to decline after a period with no exercise, in as little as one to two days, even if you’re normally active.

remember Many athletes report that their total insulin requirements increase after two to three days without regular exercise (such as when they’re too busy to exercise or are injured or ill).

Monitoring Effects of Other Medications

Other medications that don’t have a direct effect on your blood glucose can still impact your ability to be physically active, while others have no influence at all. The following sections break down some of the categories other medications you may be taking fall into so you can assess your risk.

Non-diabetes medications with exercise effects

You may be taking medications to lower your blood cholesterol, manage blood pressure, or control other cardiovascular problems. Certain medications for each of these health issues can have an impact on exercise.

Statins

Statins are a class of medications you may be taking to lower cholesterol levels or abnormal levels of blood fats to reduce your risk of having heart attack or stroke. Brand names include Altoprev, Crestor, Lescol, Lipitor, Livalo, Mevacor, Pravachol, and Zocor. In individuals who are unwilling or unable to change their diets and lifestyles sufficiently or have genetically high levels of blood fat (lipids), the benefits of statins on lowering cardiovascular risk likely greatly exceed the risks.

Statin use can cause undesirable muscular effects, such as unexplained muscle pain and weakness with physical activity that may be related to these medications’ compromising the ability of your muscles to generate energy. The occurrence of muscular conditions like myalgia, mild or severe myositis, and rhabdomyolysis, although relatively rare, is doubled in people with diabetes. Others have reported an increased susceptibility to exercise-induced muscle injury when taking statins, particularly active, older individuals. Other symptoms, such as muscle cramps during or after exercise, nocturnal cramping, and general fatigue, generally resolve when you stop taking them. If you experience any of these symptoms, talk with your doctor about switching to another cholesterol-lowering drug.

warning A major issue related to statins is that their long-term use negatively impacts the organization of collagen and decreases the biomechanical strength of the tendons and ligaments (which connect muscles to bones and stabilize your joints). These changes make them more predisposed to ruptures. In fact, statin users experience more spontaneous ruptures of both their biceps and Achilles tendons.

Talk to your doctor about whether you may be able to manage your cardiovascular risk and lipid levels without taking statins long-term for this reason. The potential impact of other cholesterol medications like Repatha (which is injected) on muscles and joints is presently unknown.

Beta-blockers

Beta-blockers (such as Lopressor, Inderal, Levatol, Corgard, Tenormin, and Zebeta) treat heart disease and hypertension (high blood pressure). These medications lower both your resting and your exercise heart rate. If you’re taking one, your heart rate doesn’t reach an age-expected value at any intensity of exercise, and your ability to reach greater intensities is likely compromised. Take them as prescribed, but just be aware of how your exercise responses may differ from normal.

warning Beta-blockers also blunt your normal hormonal response to hypoglycemia and exercise and increase your risk of more severe lows.

Diuretics

Diuretics — often known as “water pills” — such as Lasix, Microzide, Enduron, and Lozol that reduce the amount of water in your body lower blood pressure, but they can also lead to dehydration if you lose too much fluid. They aren’t likely to affect your blood glucose, although they may interfere with insulin secretion.

warning Using diuretics can cause low blood pressure, dehydration, and dizziness during exercise.

Vasodilators (nitroglycerin)

Taking vasodilators like nitroglycerin allows more blood to flow to your heart during exercise. These medications are used to treat chest pain (angina) both at rest and during exercise.

warning Vasodilators can also induce hypotension, or a drop in your blood pressure that may cause you to faint during or following an activity.

Blood thinners

warning Aspirin and other blood thinners (such as Coumadin) have the potential to make you bruise more easily or extensively in response to athletic injuries. They usually don’t have any impact on your ability to exercise, though.

Other medications with no exercise effects

If you take ACE inhibitors (for example, Capoten, Accupril, Vasotec, Lotensin, or Zestril) or angiotensin II receptor blockers (ARBs, such as Cozaar, Benicar, and Avapro) to reduce your blood pressure or protect your kidneys from possible damage, you should expect no negative effects during exercise. In fact, using certain ACE inhibitors may lower your risk of a heart attack during exercise if you have heart disease.

Other medications that treat heart disease and high blood pressure (calcium-channel blockers like Procardia, Sular, Cardene, Cardizem, and Norvasc), depression (such as Wellbutrin and Prozac), or chronic pain (Celebrex) have no effect on exercise.

Non-diabetes medications affecting blood glucose

Very few non-diabetes medications have a direct impact on your blood glucose levels. The exception is any type of corticosteroids — like Prednisone or cortisone (pills or injections into inflamed joints) — which make you more insulin resistant and cause blood glucose to rise, sometimes dramatically. Statins also raise the overall risk of developing type 2 diabetes. (Head to the earlier section “Statins” for information on how these drugs affect exercise risk as well.)

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