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How many factors actually affect blood glucose?

By Adam Brown

A printable, colorful PDF version of this article can be found here, and an updated list with 42 Factors can be found here.

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twitter summary: Adam identifies at least 22 things that affect blood glucose, including food, medication, activity, biological, & environmental factors.

short summary: As patients, we tend to blame ourselves for out of range blood sugars – after all, the equation to “good diabetes management” is supposedly simple (eating, exercise, medication). But have you ever done everything right and still had a glucose that was too high or too low? In this article, I look into the wide variety of things that can actually affect blood glucose - at least 22! – including food, medication, activity, and both biological and environmental factors. The bottom line is that diabetes is very complicated, and for even the most educated and diligent patients, it’s nearly impossible to keep track of everything that affects blood glucose. So when you see an out-of-range glucose value, don’t judge yourself – use it as information to make better decisions.

As a patient, I always fall into the trap of thinking I’m at fault for out of range blood sugars. By taking my medication, monitoring my blood glucose, watching what I eat, and exercising, I would like to have perfect in-range values all the time. But after 13 years of type 1 diabetes, I’ve learned it’s just not that simple. There are all kinds of factors that affect blood glucose, many of which are impossible to control, remember, or even account for.

Based on personal experience, conversations with experts, and scientific research, here’s a non-exhaustive list of 22 factors that can affect blood glucose. They are separated into five areas – Food, Medication, Activity, Biological factors, and Environmental factors. I’ve provided arrows to show the general effect these factors have on my blood glucose (a sideways arrow indicates a neutral effect), but emphasize that not every individual will respond in the same way (and even within the same person, you may be different from day-to-day or over time). Certain factors may also apply more to type 1 vs. type 2 diabetes (or the other way around). The best way to see how a factor affects you is through personal experience – test your blood glucose more often or wear a CGM and look for patterns. Please email me at adam.brown(at)diaTribe.org with your thoughts on this article or any factors you would add.

If you find this article useful, check out my book, Bright Spots & Landmines, available as a free PDF or for $6 at Amazon.



Typical Effect on Blood Glucose


More Info.

1. Carbohydrates


Of all the three sources of energy from food (carbohydrates, protein, and fat), carbohydrates affect my blood glucose the most. Accurately counting carbs is very difficult, and getting the number wrong can dramatically affect blood glucose. The type of carbohydrate also matters – higher glycemic index carbs tend to spike blood glucose more rapidly.

Adam’s Corner in diaTribe #58

2. Fat

Fatty foods tend to make people with diabetes more insulin resistant, meaning more insulin is often needed to cover the same amount of food relative to a similar meal without the fat. On my pump, I typically use temporary basals or extended boluses (square and dual-wave) to cover high-fat meals. This effect is most notable if you eat a lot of fat at one time – for instance, when snacking on nuts, I’ll observe a steady rise in blood glucose over many hours.

Wolpert et al., Diabetes Care 2013

3. Protein



If you’ve ever eaten a protein-only meal with very few carbs (e.g., salad with chicken), you may have seen a noticeable rise in blood glucose (~20-50 mg/dl). Though protein typically has little effect on blood glucose, in the absence of insulin, it can raise blood glucose. When I’m eating a carb-free, protein-only meal, I still take a bit of insulin to cover it (usually an equivalent of about 10-15 g of carbs)

Franz, Diabetes Educator 1997


Smart et al, Diabetes Care 2013


4. Caffeine


Many studies have suggested that caffeine increases insulin resistance and stimulates the release of adrenaline. Personally, I know that if I have a cup of coffee, I’ll see at least a 20-30 mg/dl rise in blood glucose, particularly in the morning when I’m more insulin resistant.

Lane, Journal of Caffeine Research 2011

5. Alcohol


Normally, the liver releases glucose to maintain blood sugar levels. But when alcohol is consumed, the liver is busy breaking the alcohol down, and it reduces its output of glucose into the bloodstream. This can lead to a drop in blood sugar levels if the alcohol was consumed on an empty stomach. However, alcoholic drinks with carbohydrate-rich mixers (e.g., orange juice) can also raise blood sugar. When drinking alcohol, make sure you test your blood glucose often and that someone responsible nearby knows you have diabetes.

American Diabetes Association








Typical Effect on Blood Glucose


More Info.

6. Medication dose


For those of us with diabetes on any medication (pills or insulin injections), the dose of medication directly impacts blood glucose – in most cases (but not always), taking a higher dose of a diabetes medication means a greater blood glucose-lowering effect

Your medic-ation’s label and package insert

7. Medication timing


In addition to dose, medication timing can also be critical. For instance, taking rapid-acting insulin (Humalog, Novolog, Apidra) 20 minutes before a meal is ideal for me - it leads to a lower spike in glucose vs. taking it at the start of the meal or after the meal has concluded. Note that this works best for me, although this can vary among individuals – please consult your health care provider to discuss the optimal timing of insulin. The timing of many type 2 diabetes medications matters a lot – some can consistently be taken at any time of day (e.g., Januvia, Victoza), while others are most optimally taken at meals (e.g., metformin).

Your medic-ation’s label and package insert

8. Medication Interactions


Non-diabetes medications can interfere with your diabetes medications and blood glucose. Consult the information included in both your diabetes and non-diabetes medications.

ADA’s My Medicine Tracker




Typical Effect on Blood Glucose


More Info.

9. Light exercise

Light activity can have a surprising glucose-lowering effect – I find that walking tends to lower my blood sugar by about 1 mg/dl per minute. I have seen drops as large as 46 mg/dl in 20 minutes, more than 2 mg/dl per minute, and others see even more.

Adam’s Corner in diaTribe #51

10. High-intensity and moderate exercise


Exercise is often positioned as something that always lowers blood glucose; however, high-intensity exercise, such as sprinting or weight lifting, can sometimes raise blood glucose. This stems from the adrenaline response, which tells the body to release stored glucose. Often, I find this happens when I’m exercising in the morning on an empty stomach. But this is not a reason to avoid high intensity exercise – studies show it can improve blood glucose for one to three days post-exercise! Note that in some cases high-intensity exercise can also drop blood glucose very rapidly (2-3 mg/dl per minute), especially if you have insulin on board in your pump. The best way to see how individual exercise sessions affect your blood glucose is to test prior and after activity.

The Impact of brief, high-intensity exercise on blood glucose levels” (Diabetes Metab Syndr Obes 2013)




Typical Effect on Blood Glucose


More Info.

11. Dawn phenomenon

The “dawn phenomenon” occurs in people with and without diabetes. The term refers to the body’s daily production of hormones around 4:00-5:00 AM. During this time, the body makes less insulin and produces more glucagon, which raises blood glucose. The best way to figure out how dawn phenomenon affects you is to wear a CGM or wake up and test your blood glucose early in the morning. If you take insulin, you may need to time your dose to cover this early morning rise in glucose. Note that not everyone experiences dawn phenomenon, but it is common!

Dawn phenomenon (ADA)

12. Infusion set issues (e.g., length of wear, occlusions, air bubbles)

Infusion sets are not as well understood as we would like, and a huge number of factors can lead to higher glucose levels: air bubbles in the tubing, an occluded cannula, an infected site, or even the location of the set. If you wear a pump and your glucose is unexpectedly high, a good first step is to change your set out. I find that my glucose always tends to run higher on the third day of wearing an infusion set. In addition, I tend to get the best absorption wearing sets in my buttocks and the worst absorption in my legs – yet again, this varies among patients.

Insulin Infusion Set: The Achilles Heel of Continuous Subcutaneous Insulin Infusion” (JDST 2012)

13. Scar tissue and lipodystrophy

Using the same sites on the body for injections or infusion sets can lead to lipodystrophy and scar tissue buildup – these result in erratic absorption of insulin, leading to glycemic variability and making it harder to spend more time in range. To avoid these issues, rotate your injection/infusion sites and don't reuse needles.

Common Insulin Injection Challenges (BD)


Insulin Pump Therapy (AADE)

14. Insufficient Sleep

In my experience, I have found that I need nearly 25% more insulin on days following less than seven hours of sleep; my highest blood glucose of the day is even higher on days following little sleep; and my glucose is 21% more variable when I do not sleep enough. These findings are consistent with many studies, which have found that not getting enough sleep leads to worse diabetes control, insulin resistance, weight gain, and increased food intake.

Adam’s Corner in diaTribe #53 – see my full length article on sleep and glucose control for a more comprehensive list of related research studies

15. Stress and illness

Stress and illness can cause the body to release epinephrine (adrenaline), glucagon, growth hormone, and cortisol. As a result, more glucose is released from the liver (glucagon, adrenaline) and the body can become less sensitive to insulin (growth hormone, cortisol). In some cases, people are much more insulin sensitive right before getting sick and can tend to run low blood sugars. Personally, I have found exercise, time outside, and meditation to be most helpful against combatting stress.

UCSF Diabetes Education



16. Allergies

Though I have not found any studies on this topic, some patients report higher glucose levels when they have allergies. Some have speculated that it’s due to the stress hormone cortisol.

Can allergies raise glucose level? (Diabetes Forums)


Allergies and Blood Sugar (TuDiabetes)


17. A higher glucose level (“glucotoxicity”)

Hyperglycemia can lead to a state known as “glucotoxicity,” which can actually cause insulin resistance. Have you ever needed to correct a very high blood sugar with much more insulin than your correction factor would suggest? I find that simply having a high blood glucose for many hours makes me appear much more insulin resistant.

Vuorinen-Markkola et al., Diabetes 1992


Kim et al., Circulation 2006

18. Periods (Menstruation)


There is not a definite answer to the question of how periods affect women’s blood sugars. Many women report having higher blood sugar levels a few days prior to their period starting, but some women notice a sharp drop in sugar levels. To figure out how you respond, your best bet is to test your blood glucose often during this time of month.

Periods (Menstruation) and Diabetes (Diabetes UK)


Why are my blood sugars affected by my period? (DiabetesSisters)

19. Smoking

Some studies suggest that smoking can increase insulin resistance, and people with diabetes who smoke are more likely than nonsmokers to have trouble with insulin dosing and managing their diabetes. Smokers also have higher risks for serious complications.



Chiolero et al, AJCN 2008





Typical Effect on Blood Glucose


More Info.

20. Insulin that has gone bad

I’ve fried my insulin by exposing it to direct sunlight or leaving it in the car on a hot day. If your insulin is normally clear, but suddenly turns cloudy, that could signal it has gone bad (note: NPH is always cloudy). Aside from a change in appearance, it can be hard to know if a vial of insulin has actually gone bad unless you try a new one. I’ve found that insulin that has “gone bad” will typically still work, but just not as well – I may need more insulin than I think to bring my glucose down, and the insulin may work unpredictably. Unopened insulin should be stored in a refrigerator at approximately 36-46 °F. According to the FDA, insulin can be left unrefrigerated at a temperature from 59-86 °F for up to 28 days.

Information regarding insulin storage (FDA)

 21. An inaccurate blood glucose reading

While this seems fairly obvious, I often find myself testing multiple times in a row, since I do not believe the initial value – in many cases, the second time I get a much lower value, and it’s because I failed to wash my hands. For a meter that needs a tiny 0.3 microliter blood sample (the smallest currently on the market), a speck of glucose on the finger the weight of a dust particle will falsely increase the reading by 300 mg/dl! I recommend rechecking if you don’t believe the value on the meter; if you wear CGM, it’s great to reality check the meter value against your sensor reading. The diabetes online community has also done a lot of work advocating for more accurate blood glucose testing supplies – you can read more about their campaign here.

Glucose Monitoring After Fruit Peeling (Diabetes Care 2011)

22. Altitude


Though most studies related to diabetes and altitude concern the accuracy of blood glucose meters, there are some reports that altitude can increase insulin resistance. I’ve found that when I go to high altitude regions like Colorado, I need about 20-30% more basal insulin. However, if you go to a high altitude place to do activity (e.g., skiing), you may find that you need less insulin.

High Altitude Diabetes (A Sweet Life)


Blood Glucose and Altitude (Diabetes Forecast)

February 2018 Update: Get an expanded list with 20 additional factors here. This update brings the total to 42 factors, including a whole new category on behavior and decisions.

[Editor’s Note: Adam is a patient with diabetes and not a health care provider. Please consult with your health care provider before making any changes to your diet, insulin, or medication regimen.]

Adam is Senior Editor of diaTribe and Chief of Staff/Head, Diabetes Technology at Close Concerns. He is a graduate of the University of Pennsylvania and serves on the board of the San Francisco branch of JDRF. He was diagnosed with type 1 diabetes at the age of 12 and has worn an insulin pump for the last 12 years and a CGM for the past four years. Adam is passionate about exercise, nutrition, and wellness and spends his free time outdoors and staying active. He can be contacted at adam.brown(at)diatribe.org or @asbrown1 on twitter.