Overbasalization in Type 1 and Type 2 Diabetes: You Can Have Too Much of a Good Thing!

Overbasalization in Type 1 and Type 2

It’s a universally acknowledged truth that a person with diabetes who has an elevated A1c must be in want of more basal insulin to bring their A1c down, right?

Not necessarily!

The Role of Long-Acting Basal Insulin

For people with type 1 diabetes, and many people with type 2, long-acting basal insulin is used to manage the body’s underlying continuous blood sugar needs between meals and periods of fasting (like overnight). It works primarily by increasing blood sugar uptake by the muscles. It also decreases sugar production by the liver which is usually in excess, especially in type 2 diabetes.

For the most part, basal insulin is fairly static, hovering in the background like a drone over a parade, or my mother at my first school dance.  But unlike my mother, basal insulin (such as Lantus, BASAGLAR, Levemir, Toujeo, and Tresiba) is unable to adequately manage the variations of day-to-day food intake. Basal insulin does not adapt to the spike in blood sugar that follows a carbohydrate load; this job is reserved for the shorter-acting bolus or premeal insulin (such as Regular, Humalog, Novolog, Fiasp, and Lyumjev) that must be dosed multiple times a day before meals and to correct for unexpected high glucose levels. Therefore, an appropriate basal insulin dose should keep your fasting blood sugar at goal, but your daytime postprandial (after meal) blood sugars can still run quite high, leading to an elevated A1c. Thus, the practice of insulin overbasalization was unintentionally born.

What Does Overbasalization Mean?

Overbasalization of insulin typically describes an increase in basal insulin doses in an attempt to control daytime highs. Overbasalization may happen for several reasons. A clinician may see an elevated A1c as a sign to intensify all insulin therapy, not realizing that the fasting morning sugar may actually be at goal. It may result from fear or hesitation of initiating short-acting bolus insulin on behalf of the clinician or the person with diabetes, and therefore the basal insulin dose continues to be increased instead. It may result from a clinician not realizing that an elevated A1c is caused by the person not being able to consistently take their basal or bolus insulin, and thus insulin prescriptions are increased unnecessarily.

How Do You Know If You Have Too Much, Too Little, or the Right Amount of Basal Insulin?

  • If your blood sugar drops low overnight or in the early morning, you might have too much basal insulin.
  • If your blood sugar drops low when you skip a meal, you might have too much basal insulin.
  • If your fasting morning blood sugar is 50 points lower than your bedtime blood sugar, you might have too much basal insulin.
  • If your A1c is not improving with increasing basal insulin doses, you might have too much basal insulin.
  • If you wake up with a fasting blood glucose between 80-130 and you go to bed in that same range, you might have the right amount of basal insulin.

As you can see, one of the main concerns with insulin overbasalization relates to recurrent hypoglycemia, often in the setting of a seemingly paradoxically elevated A1c.

A common scenario is when healthcare providers start basal insulin in people with T2D and up titrate the dose to get the morning glucose under control. The problem occurs when people have elevated glucose values after dinner, leading to elevated glucose values all night and into the morning. The HCP then increases the dose until the morning value is in range. This is a classic setup for overbasalization…bringing down the postmeal glucose by increasing the basal insulin. This is a setup for hypoglycemia overnight when someone goes to bed with a good glucose value (perhaps because they ate less or exercised) and then they take their usual basal insulin dose, which now is too high.

Individualized Insulin Regimens and Paired Testing

This further highlights the important point that every insulin regimen needs to be individualized to the person living with diabetes, with an assessment of multiple day-to-day blood sugars as the best way to determine what kind of insulin changes are best to avoid overbasalization. We call this paired testing. Paired testing is when a person with diabetes tests their blood sugars before bed and again first thing in the morning. If the glucose level drops more than 30 or 40 points, then the basal dose may be too high. If the glucose level stays roughly the same, the basal dose is in the ideal range. If the glucose level goes up 30 or 40 points, then the basal dose may be too low.

What if someone’s bedtime glucose value is around 200 points, does not change overnight, and is still 200 when they wake up? This means the basal dose is just right, and the goal now is to get the bedtime glucose down by controlling the post-dinner glucose value.

If the person in the example above never did paired testing and only looked at the morning value, they would likely increase their basal dose night after night until they ended up crashing with a low. This is a classic scenario of overbasalization.

The Takeaway

The bottom line is that overbasalization can occur if you do not do paired testing overnight to find the cause of an elevated morning value. It’s a crucial step to take in determining the right insulin regimen for you.


Additional Resources:

How to Treat Foot to Floor Phenomenon

Dawn Phenomenon: How to Identify and Manage It

  1. Avatar

    My BG drops overnight seems like no matter what I do. I have a new awareness (besides my CGM) because I tend to get very numb hands that wake me up. I know the basal must be set too high, even though it’s only at .45. I do not know when to change it. Is there still a two hour lookback rule? Would the Omnipod 5 help?
    I tend to stay up late and get up between 8 and 8:45. Definitely a night owl.

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