Is there an ideal time to do physical activity with type 1 diabetes?

Physical activity can be a powerful tool for improving quality of life and overall well-being. But if you or your child are living with type 1 diabetes (T1D), doing physical activity can also complicate blood sugar management and increase its variability.

The risks of hypo- and hyperglycemia are greater not only during physical activity, but also in the following hours. Variations in blood sugar levels generally depend on a number of factors, such as the type of activity (e.g., running vs. weight training), duration, intensity, level of active insulin (i.e., the amount of insulin that is still in effect following a bolus), outside temperature, etc. 

However, there are many ways to mitigate this risk, such as reducing insulin or eating a snack. Have you ever wondered whether there’s a better time of day to be physically active when you live with T1D? Is there a moment where it would be easier to predict the expected variation in blood sugar and simplify its management?

The American Diabetes Association recently published a brief review of scientific studies on the impact of physical activity depending on the time of day. Here’s a summary of what was discovered. 

Morning vs. afternoon

Doing endurance exercise (e.g., swimming, cycling on a flat surface) on an empty stomach in the morning rather than in the afternoon could help reduce the risk of hypoglycemia and increase the time spent in the target range. Blood sugar levels should drop only slightly, even without any meal or snack.

Doing high intensity exercise (e.g., high intensity interval training, sprints) in the morning may result in a greater rise in blood sugar levels, but may also help reduce the risk of post-workout hypoglycemia (especially overnight) compared to doing it in the afternoon.

Both of these observations can be explained by the higher level of certain hormones in the morning, such as cortisol. Cortisol gets the body ready the body for waking, and also acts as a growth hormone in adulthood. These hormones are also involved in the dawn phenomenon.

On the other hand, doing resistance exercise (e.g., lifting weights) in the afternoon can help improve the stability of blood sugar levels following exercise as opposed to doing this type of activity in the morning, when it often leads to higher blood sugar levels and greater variability.

Before a meal vs. after a meal

After a meal, blood sugar levels naturally tend to rise. Doing light or moderate exercise after a meal (e.g., a 15-30 minute walk) can help to lower your blood sugar levels. But if this activity lasts more than 30 minutes and the mealtime insulin dose was not reduced, the risk of hypoglycemia increases rapidly.

In order to prevent the risk of hypoglycemia when doing physical activity, it might be best to do endurance exercise before meals, as there is less insulin in action in the body at that time.

It’s important to note, however, that the risk of hypoglycemia is generally lower for high intensity exercise (e.g., sprints) and resistance exercise (e.g., weight training) than it is for endurance exercise (e.g., running, cycling), regardless of the time a meal is taken.

Listen to your body: the best time is your time!

There are a number of constraints that can dictate the time you have available for physical activity, including your professional and personal responsibilities (e.g., work schedule, family life) or your natural preference to be active in the morning or evening. Children and teenagers living with T1D often do physical activity spontaneously throughout the day.

At all times, continuous glucose monitors (CGMs) are invaluable tools for understanding and assessing the impact of physical activity on blood sugar levels. It’s important to remember, however, that the sensor measures blood sugar in the interstitial fluid under the skin and therefore always lags slightly behind capillary blood glucose measured at the fingertip. You must take into account that the lag is generally a little longer during physical activity, when blood sugar levels change more rapidly. For instance, if your sensor indicates 4.3 mmol/L with a downward trend arrow during your workout, your blood sugar is probably already lower than the value displayed. In this case, it’s best to stop your workout and treat the hypoglycemia. 

It’s important to keep in mind that everyone is different. While scientific studies can provide general guidelines, the best time to exercise is whatever time that suits you best. Listen to your body and take into account your routine, schedule and personal preferences. If you notice fluctuations in blood sugar levels or unusual reactions, take note of these observations and adjust your routine accordingly.

Scientific studies suggest that doing physical activity at certain times (e.g., in the morning on an empty stomach and after meals) may provide optimal benefits on blood sugar levels, but there is no universal answer, and it’s always a good time to be active!

So, go for it! Try different approaches, listen to your body and find the pace you’re the most comfortable with.

References:

• Riddell, Michael C. et al. Is There an Optimal Time of Day for Exercise? A Commentary on When to Exercise for People Living With Type 1 or Type 2 Diabetes. Diabetes spectrum : a publication of the American Diabetes Association vol. 36,2 (2023): 146-150. doi:10.2337/dsi22-0017
• Yardley, Jane E. Reassessing the evidence: prandial state dictates glycaemic responses to exercise in individuals with type 1 diabetes to a greater extent than intensity. Diabetologia vol. 65,12 (2022) : 1994-1999. doi:10.1007/s00125-022-05781-8
• Huynh, Lyly, Haag, Sarah and Roy-Fleming, Amélie. Diabète de type 1 – Recommandations et stratégies pour l’activité physique. Revue Plein Soleil, hiver 2021-2022. https://type1better.com/wp-content/uploads/2021/12/2021_PS4_IRCM.pdf [In French only].