Factors that Affect Blood Glucose

Why is BG High? or Low? factors that affect blood glucose

A number of factors impact your child’s blood glucose reading at any given moment in time. To maximize the time your child spends in their target range, we need to balance these factors. But let's be gentle with ourselves, because the balancing act isn't easy! Some factors decrease blood glucose, while other raise it. But which are which? Under what conditions? And what about those sneaky, lesser-known causes of BG swings? Read on to reduce the swings (and your child’s A1C).

As we said, managing blood sugar is a balancing act. The major players are food, physical activity, medication and hormones.

In a nutshell, carbs and hormones raise blood glucose, while insulin (medication) and exercise lower it.

Factors That Raise Blood Glucose

Food and Drink Consumed

When your child eats foods containing carbohydrates (and protein, to some degree), her blood glucose will rise.

The goal in managing post-meal glucose levels is to match the food bolus (insulin dose to cover food) as closely as possible to the food consumed, so that blood glucose rises as little as possible, and returns to the target range after meals and snacks.

More on the effect of FOOD on blood sugar:

Nutrition section


If your child is in a growth spurt, has entered puberty, is menstruating, is in a period of elevated stress or excitement (such as exam time, travel, or exciting visits with grandparents or to an amusement park), you may need to make adjustments to the insulin she receives, possibly giving more insulin than her body would require in non-growth, non-stress, non-hormonal times.

Tips from the Trenches

When we travel, even if activity levels stay about the same, we find that because of stress and excitement, we need to increase our son’s basal insulin significantly or else we are constantly battling high blood glucose.

Factors That Lower Blood Glucose


Your child’s blood glucose will be affected by the amount of insulin that is currently acting (from recent insulin doses), including:

You may find that changes need to be made periodically to these rates and ratios to meet the changing needs of your child’s body for insulin. Also, If your child is on a Conventional Insulin Program and there have been or will be changes in his eating habits/planned meals, insulin doses may need to be adjusted.


If your child will be participating in planned exercise, you may need to adjust insulin doses or provide extra carbs to accommodate for the blood-glucose-lowering effect of physical activity.

More on the effect of physical activity on blood sugar:

But That's Not the Whole Story...

There are many other lesser-known factors that also weigh in on the blood glucose balancing act. In fact, Adam Brown (for diaTribe) counts over 3 dozen of them (!) of them in 42 Factors That Affect Blood Glucose?! A Surprising Update. To further complicate things, some factors can either raise or lower glucose levels.

Let's take a look...

Food & Drink

Here are some other food-related factors that impact your child's blood glucose:

  • Amount of Carbs ( blood glucose)

We've already talked in general about how the amount of carbs that your child eats will affect his blood sugar. But here are some additional things to consider when it comes to carbohydrates:

    • Having an accurate carb-count affects blood glucose levels after eating. Did you nail the carb-counting? Did you have to wildly guess?
    • Were ALL of the carbs covered with insulin? It's great when our kids are getting more independent with insulin delivery, but sometimes a meal bolus is missed, or they remember to bolus for the first serving, but not for the second. Also, some kids like to graze. When they do, they can have a couple of grams of carbs here, and few more there, until they have eaten way more than anyone would have guessed. If the sum-total of carbs isn’t covered by insulin, blood sugar will rise.
    • Eating a huge amount of carbs in one sitting requires proportionally more insulin than if your teen had eaten a small amount of carbs at that same sitting.
  • Type of Carbs (or or  blood glucose): There’s a difference between how 30g of carbs in mashed potatoes affects blood glucose, versus 30g of carbs in a banana. Some carbs digest quickly, while others digest slowly. This is related to the concept of Glycemic Index). In short, the quality of carbs affects blood glucose differently, and the affect lasts for different amounts of time post-meal.
  • Combination of foods in the meal: If your child eats protein or fat with carbs, this will slow down digestion and flatten post-meal BG spikes.
  • Timing of a Meal: Eating a late-night meal may lead to higher overnight blood glucose than eating earlier in the evening. (This one is my arch enemy now that our son is a teenager.)
  • Fat: High-fat foods lead to insulin resistance, which raises glucose levels.
  • Protein: Eating large amounts of protein in the absence of carbs leads to a gradual rise in blood glucose.
  •  Caffeine increases insulin resistance and causes the release of adrenaline, leading to a rise in blood sugar.
  • Alcohol: Sweet drinks will raise BG in the short term; but the alcohol itself drops BG hours later.
  • Mind-altering Drugs affect decision-making, which may lead to missed insulin doses, or to mis-dosing insulin. Also, they may get the munchies and eat snacks that they forget to bolus for.
  • Dehydration: When your body is under-hydrated, the hormone vasopressin is released to help retain water. But vasopressin also has a blood-glucose-raising effect, as it causes the liver to release stored glucose.


  • Timing of insulin: Whether insulin is given well before eating (15-20 minutes), right before eating, or after eating affects how effective it is at keeping blood glucose steady.
  • Amount of Insulin (Dose): Insulin needs change over time, as kids grow, as soccer season starts, and then again when it ends. If the insulin dosing is not tweaked regularly to keep pace with their changing needs, your child/teen may not be getting the correct amount of insulin. 
    • Basal insulin
    • Bolus Insulin for food, expressed as an insulin-to-carb ratio, or I:C
    • Bolus insulin to correct high blood glucose. expressed as a Correction Factor, sliding scale, or Insulin Sensitivity factor (ISF)
    • Size of bolus – a huge bolus is less effective, as the injection or pump site gets saturated and so cannot absorb the insulin as well as if it is delivered more slowly.
  • Steroids (such as prednisone; some allergy meds; asthma inhalers) increase insulin resistance, and so raise blood sugar.
  • Vitamins: Vitamin C (high dose) raises blood glucose, as does Niacin (vitamin B3).


  • The degree of intensity of physical activity affects if, or how much, blood sugar is affected.:
    • You may see a slight drop in BG after light exercise
    • A slow and steady walk that lasts for a while (for example a long dog stroll, or a day walking around an amusement park) may result in a bigger dip that will last longer.
    • Intense physical activity that gets your child huffing and puffing will lead to a quicker, bigger drop in BG 
  • Adrenaline-inducing, anaerobic exercise has the opposite affect, raising BG during exercise
    • Lifting, Resistance Training
    • HIIT (Hi-Intensity Interval Training): short bursts of intense exercise
    • Hill sprints in which you push hard up the hill then jog gently back down
    • Competitive and really want to win, then adrenaline spikes - and so does blood sugar
    • Games are more likely to lead to a BG rise than practices, which may lead to falling blood glucose
  • Amount of time since the physical activity ended: Steady or intense exercise may continue to cause blood glucose to fall for several hours after the activity ends.
  • Time of day: the way that you adjust for exercise in the morning may be different from the afternoon or evening, due to your differing insulin sensitivity at different times of day
  • Your level of fitness: the more fit you are, the less energy it takes to engage in a given activity, and so the less blood glucose will drop (compared to the beginning of your fitness journey, when you were less physically fit).

More on the effect of physical activity on blood sugar:

More on physical activity that could RAISE blood sugar:

Illness, Hormones & Other Biological Factors

  • Illness: If your child is sick, his insulin doses will likely need to be adjusted (either up or down) throughout the course of the illness.

Tips from the Trenches

We have found that our son has several unexplainable lows for about 3 days before he shows symptoms of a cold or flu-like illness. Just when we’re wondering “what the heck is going on here?!” he starts to cough or get congested, and then it all makes sense. 

We've also noticed that when he has a cold or flu, it's like T1D goes on vacation; his blood glucose is steadier and easier to manage then it ever is when he's feeling well. Go figure.


  • Menstruation
    • Most girls have an increased need for insulin in the 3-7 days before her period begins. For some girls, insulin needs decrease during this time. 
    • Then insulin needs usually fall once her cycle starts.
    • Around Day 11-18, hormones rise for 2 or 3 days because of ovulation, so insulin needs increase again, then drop back down until the they ramp up again in the 3-7 days before her period, as above. 
  • Puberty: insulin needs increase because of increasing hormone levels.
  • Dawn Phenomenon: For teens and adults, insulin needs are greater in the early morning hours than at other times of the day.
  • Growth Hormones in Kids:
    • When your child or teen is going through a growth spurt, their insulin needs increase across the board.
    • During this time, soon after your child/teen falls sleep, growth hormone is released into the blood stream, resulting in a rise in blood glucose. So the basal rate around bed-time may need to be higher that at other times of the day (during times of physical growth).
  • During Sleep some kids drop, while others tend to rise.
  • Recent lows (hypoglycemia): Having a low BG increases the risk of further lows, due at least in part to the body speeding up stomach-emptying, to get glucose into the blood stream to counteract the low. This effect can persist for hours after a low.
  • High BG (glucotoxicity):
    • Once BG is high (over 14 mmol/L) you need proportionally more insulin to bring it back down. (If our teen son has BG over 15 mmol/L, we often need to double the correction dose for it to be effective.)
    • If BG is high for prolonged period, insulin needs increase, due at least in part to insulin resistance.
  • Stress (school tests, road rage, excitement about a birthday party) most commonly causes high blood sugar, but some kids find that they are more likely to experience lows just before or during school exams.
  • Allergies – histamine reaction causes inflammation in the body, creates stress in the body so insulin needs increase (medications may also affect BG, especially if the allergy med has a steroid component)
  • Intense Pain (injury, severe headaches/migraines, surgery, broken bone) causes stress in the body, and so leads to high blood glucose.
  • Sunburn is a stressor, and so leads to high blood glucose.
  • Smoking makes you insulin resistant, perhaps because of an inflammatory response in the lungs.
  • Over-tired / too little sleep causes stress in the body.
  • Undiagnosed, Untreated Celiac Disease can lead to unpredictable glucose swings in both directions, largely due to the inefficient digestion of food, as well as body inflammation.
  • Mental Health Struggles
    • Depression and anxiety are a stress on your body and so (along with behaviour changes and a likely decline in self-care) lead to high blood sugar.
    • Diabetes-related Eating Disorders may cause under-dosing of insulin (which will cause high blood glucose).
  • Weight Gain: If overweight, you are more insulin resistant, and so will need more insulin than you did previously.
  • Problems with the injection site or infusion set/site
    • Bent cannula
    • Scar tissue / lipodystrophy:  If you over-use a site, scar tissue develops, so insulin will not absorb as well at that site and high BG will result. If you then switch to a new site, the insulin will be absorbed better and so have more effect, which could lead to lows.
    • On the third day using the same infusion set, blood glucose may rise, as the insulin loses effectiveness AND absorption at the site is reduced.

When your child experiences any of the above factors, or you notice that her blood glucose is often below or above the target range, you may want to explore some of these factors in more detail. For more information, click on any of the underlined topics above for more information. Many parents choose to consult with their child’s diabetes health care team for assistance with changes to the blood glucose management regime.


  • 2.

    Juicebox Podcast Ep 231. Diabetes Pro-Tip: Variables

    Scott Benner (parent of a teen with T1D) and Jennifer Smith, RD (Registered Dietician), CDE (Certified Diabetes Educator)