You ate the same thing at the same time, and today's number is not yesterday's. If that has ever puzzled you, here is the plain answer: glucose responds to a lot more than your plate. Food, medicines and physical activity all change blood sugar through the day [2], and so do illness, sleep and a few other things. Below is what published sources say about each one, in everyday words. It is general information from the sources listed at the end, not advice for your situation. Your own care team is the place for questions about your numbers.
Food: carbs become glucose
Start with the one everybody knows. Your body turns carbohydrates from food into glucose, which can raise your blood glucose level [1]. Carbs are not spread evenly across foods: some fruits, beans and starchy vegetables have more of them than other foods [1]. So two meals that look similar on a plate can differ in how many carbs they hold.
Movement: usually down, sometimes up
Physical activity often lowers the level of glucose in your blood [1]. Working out puts your muscles to work, and working muscles burn glucose; activity also improves how insulin works [3]. The effect can outlast the workout: after activity, glucose may stay low for hours or days [1]. Low glucose is most likely for people who take insulin or some other diabetes medicines, such as sulfonylureas [1].
Then comes the twist. Some workouts make your body produce stress hormones such as adrenaline, and adrenaline raises glucose by stimulating the liver to release it [3]. So movement does not always pull in one direction.
| Factor | What the sources describe |
|---|---|
| Food (carbs) | Carbs from food turn into glucose, which can raise it |
| Physical activity | Often lowers it, sometimes for hours or days; some workouts can raise it |
| Illness | Hormones that fight illness can raise it; fever, sweating and poor appetite can lower it |
| Sleep | Too much or too little may raise it |
| Alcohol | With insulin or certain diabetes medicines, can make it drop too low |
Being sick: your own hormones join in
If you do get sick, you may notice your blood sugar is higher than usual [4]. The reason: to fight off illness, your immune system releases hormones, and those hormones can raise your blood sugar temporarily [4] [5]. Some cold and flu medicines can raise it too [4]. And it can pull the other way: fever, sweating and poor appetite can cause low blood sugar [4]. Blood sugar can be hard to manage on a sick day [5].
Sleep: too little or too much
Sleeping too much or too little may raise your blood glucose levels [1].
The rest of the cast
Medicines are on the list of things that move blood sugar through the day [2]. Some diabetes medicines can make glucose drop too low during exercise, or when a meal is skipped or delayed [1]. For people taking insulin or certain diabetes medicines, drinking alcohol can also make glucose drop too low [1]. The sources here do not describe how stress affects glucose; one lists it, with food and activity, among the things to note beside a reading [6].
Why a note beside the number helps
With this many things pulling at once, a number on its own rarely says why it is what it is. A short note about food, activity or stress turns it into something you can read: a number with a note beside it can show what was going on [6]. Over days, those notes can start to show a pattern. For what to write down and how to keep it, see the post on keeping a glucose log, and for why timing changes what a reading means, see the post on fasting, post-meal and random readings.
Sources
- National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), Healthy Living with Diabetes.
- Centers for Disease Control and Prevention, Monitoring Your Blood Sugar.
- American Diabetes Association, Exercise and Blood Glucose Levels in Diabetes.
- Centers for Disease Control and Prevention, Your Immune System and Diabetes.
- Centers for Disease Control and Prevention, Managing Sick Days.
- American Diabetes Association, Check Your Blood Glucose.
We made Steadion, an iPhone tracker for people with diabetes or prediabetes. In it you can log a fingerstick reading by hand, or photograph your meter and let Steadion read the number off it. You confirm the number before it saves. Readings save back to Apple Health, and trend charts show them over time. Learn more at steadion.fit.