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The Overnight Blood Sugar Conundrum

By Adam Brown

How do I stay in range while sleeping?

In the past week, I’ve seen these two 24-hour CGM traces:

It’s amazing that the same overnight insulin dose produced those two markedly different midnight-to-9am glucose outcomes (left side of each graph).

The example on the right, I believe, was caused by: (i) a big late-night dinner after barely eating all day, and (ii) changing my pump’s infusion set and reservoir right before bed, without confirming a few hours later that it was working properly.

Whatever the cause, I woke up at 7:50 am on Tuesday at 262 mg/dl – exhausted, frustrated, and late for a team event. I changed my pump site quickly, took a huge six-unit insulin bolus, and decided at the last minute to ride my bike 4.5 miles to the event.

Halfway down the steep hill from my house, I had that sinking feeling: “Gah! I should go back home and get glucose tabs, just in case.” I cycled back, grabbed the tabs, and then my prediction turned out to be correct 15 minutes later – halfway to the event, my glucose was dropping faster than I’d ever seen in my life. I ate three tabs as a buffer and luckily avoided going low.

By 9:05 am, I had arrived for our team photo event covered in embarrassing business-casual sweat, but back in range. And from there, the workday could actually begin.

I tell this story to illustrate a larger point – overnight blood sugar has a major impact on the next day. Unfortunately, keeping glucose in range every single night is very difficult without an automated system. This article shares some of my Bright Spots for beating this nighttime conundrum, gleaned from those nights like the example above on the left. Enjoy, and get all my Bright Spots & Landmines here (free PDF) or at Amazon.

Overnight BGs in a tight, safe range (80-140 mg/dl): early dinner, no snacking, disciplined bedtime corrections

Keeping my blood glucose (BG) in a tight, safe range overnight (80-140 mg/dl) dramatically improves my sleep quality and next-day restfulness. Nighttime highs and lows really disrupt sleep, and the more dramatic or prolonged they are, the worse I end up feeling the following morning: exhausted, grumpy, and likely to either overeat (to correct a low) or remain high for much of the next day.

What makes nighttime BGs profoundly difficult is that they are influenced by a number of factors: food during the day; dinner and nighttime snacking (size, type, timing); daytime exercise; insulin dose and timing; and more. Basal insulin requirements can also change drastically from night to night – in studies of automated insulin delivery, people with diabetes sometimes need half as much basal insulin on some nights and twice as much insulin on other nights. This makes repeatable perfection challenging!

Nighttime is also a scary time to live with diabetes – given the potential for severe hypoglycemia – so my instinct is to be ultra conservative before bed with food (eating too much) and insulin dosing (taking too little). Upcoming automated insulin delivery systems will be a major overnight Bright Spot, but not everyone may want to or be able to use them.

When I have a Bright Spot night of BGs (80-140 mg/dl), there are usually some key enablers:

  • I have a filling early dinner with lots of veggies, a modest portion of protein, and plenty of fluids at least three hours before bed.

  • I stick to a black-and-white rule to prevent snacking – I do NOT eat after dinner unless I’m low.

  • I correct lows before bed with a quantity-limited food (a small apple, glucose tabs, Smarties), eating just enough to get back to my target range. 

Just as with food, glucose monitoring (ideally with CGM) is the key feedback mechanism for this Bright Spot – am I consistently going high or low during sleep? How does my BG usually change from pre-bed to waking up? What might be driving the pattern, particularly my food habits?

I’m careful about changing my overnight basal insulin dose from night to night, since my routine tends to vary minimally. I get into trouble when I use one isolated night of BGs (e.g., two hours spent low on Monday) and impulsively change my entire weekly basal insulin plan. This is never a good idea. My personal nighttime patterns are often inconsistent (high on Monday, low on Tuesday), and I find my eating habits are typically the biggest driver. (The obvious exception is if I have a consistently high or low pattern on most nights in a period of two weeks – then I do change my basal insulin dose.)




Look for overnight BG patterns: does my BG stay relatively level throughout an average night (within about 30 mg/dl from before bed to waking up), or does it consistently rise or fall from bedtime to wakeup? If BG is consistently changing on most nights, talk to your healthcare provider about your medication dose. (Insulin users can read more on this topic from Gary Scheiner at diatribe.org/basaltesting)

On Bright Spot nights, what combination of factors may have contributed to in-range BGs? When my BG goes far out of range from pre-bed to waking up, was there an obvious driver? If this happens consistently, how might I change my eating routine or medication dose?

Focus on food it’s the biggest driver of my high and low BG patterns overnight. What foods and timing help keep me in range overnight, including dinner and nighttime snacks? Can I be more consistent with my evening eating? What bedtime low correction brings me back in range and keeps my BG stable overnight?

Remember that overnight perfection is difficult when manually dosing insulin. Strive for improvement, use data to make decisions, and experiment conservatively. I’m always in learning mode and still constantly making mistakes.

Use automated insulin delivery overnight, if it’s accessible to you (also known as a “hybrid closed loop” or “artificial pancreas”). These systems are outstanding overnight – almost every morning while wearing one, most people wake up around 90-120 mg/dl.

If using a pump in open loop (no automation), remember basal insulin changes should be made at least one hour before the actual low or high occurs (i.e., a change in basal dose takes time to actually affect my BG).


Want more tips like this? Get Bright Spots & Landmines: The Diabetes Guide I Wish Someone Had Handed Me here for free/name your own price. You can also purchase it at Amazon in paperback ($6.29) and Kindle ($1.99). The print book is priced at cost to ensure widespread access, and 100% of proceeds from digital downloads benefit The diaTribe Foundation, a 501(c)(3) non-profit.

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