February 5, 2025, 10:32 pm | Read time: 5 minutes
Exercise is healthy, but does it make a difference whether you are active in the morning, afternoon, or evening? A study from Germany has now provided some quite surprising findings. The time of day of exercise can be an influencing factor, particularly with regard to the risk of obesity and diabetes.
It is undisputed that physical activity can reduce the risk of obesity and diabetes. However, current research suggests that not only the volume of activity plays a role but also the timing. The human metabolism follows a natural daily rhythm that influences blood sugar levels, energy consumption, and insulin action, for example. Theoretically, this could mean that exercise at the right time can be more effective in reducing the risk of obesity and diabetes – but how strong are these differences really?
A team led by Michael Stein from the University of Regensburg took a closer look at this question.1 Using objective exercise data from tens of thousands of study participants, they investigated whether there is an optimal time for physical activity – and when exercise may be less beneficial.
What Exactly Was Investigated?
The researchers investigated the relationship between the time of day of physical activity and the risk of obesity (BMI ≥ 30) and diabetes. To diagnose diabetes, either a doctor’s indication or the so-called HbA1c value was used. HbA1c is also commonly referred to as long-term glucose, as it reflects the average blood glucose level over the past two to three months and is used for the long-term control of diabetes.
The background to the study is the growing realization that the body’s circadian rhythm influences not only sleep but also metabolism. In an interview with FITBOOK, the renowned chronobiologist Dr. Satchin Panda confirmed that consistently ignoring the internal clock can have health consequences. “After a few months and years, the risk of chronic illnesses such as neurodegenerative diseases, depression, anxiety, and other disorders increases,” says Panda. “It can even be a trigger for attention deficit disorder. It also increases the risk of metabolic diseases such as diabetes, fatty liver, elevated cholesterol levels, and cardiovascular disease. Moreover, it can even increase the risk of cancer.”
The circadian rhythm (the internal biological clock) also has an effect on the impact of exercise. Previous research has suggested that activity at certain times of the day may be more beneficial for sugar metabolism and weight control. At the same time, there are indications that exercise at night could have unfavorable effects.
The Structure of the Study
The study is based on a cross-sectional analysis of 61,116 participants in the NAKO Health Study, a large-scale cohort study in Germany. Between 2015 and 2019, the participants wore a hip activity sensor (ActiGraph) for seven days, which recorded their movements. The researchers analyzed the activity separately by age group and gender and divided the participants into four groups (quartiles) depending on how much they moved.
Using statistical models, they calculated the probability of obesity and diabetes depending on the time of day of activity. The scientists took into account various factors that influence this, such as age, gender, education, and lifestyle. The so-called OR value (odds ratio) indicates the extent to which the probability of a disease has changed in comparison to a reference group. A value below 1 means a lower risk; a value above 1 means an increased risk.
When is the Right Time to Exercise to Reduce the Risk of Obesity and Diabetes? The Results
The results show that the risk of obesity and diabetes differs significantly depending on the time of day of activity:
- Exercise in the afternoon is most beneficial: participants with high afternoon activity had a 64 percent lower risk of obesity (OR: 0.36) and a 53 percent lower risk of diabetes (OR: 0.47) compared to the group with the lowest afternoon activity.
- Evening activity also has positive effects: A lot of exercise in the evening was associated with a 55 percent lower risk of obesity (OR: 0.45) and a 44 percent lower risk of diabetes (OR: 0.56).
- Morning activity offered only moderate benefits: The risk for obesity was reduced by 29 percent (OR: 0.71) and for diabetes by 20 percent (OR: 0.80) – less than with later activity.
- Exercise at night is unfavorable: participants with high levels of night-time activity had a 58 percent higher risk of obesity (OR: 1.58) and a 43 percent higher risk of diabetes (OR: 1.43).
These correlations remained even after taking into account sleep duration, shift work, and employment status.
What Is the Significance of the Results?
The results suggest that it is not only exercise itself that is important in preventing obesity and diabetes, but also the right time for it. Physical activity seems to be particularly beneficial for the metabolism in the afternoon and evening. This could be related to diurnal fluctuations in insulin sensitivity, which is lowest in the afternoon and evening – precisely when exercise can help to improve glucose utilization.
People with diabetes or at increased risk of obesity could, therefore, benefit from targeted exercise or physical activity in the afternoon or evening. A walk after dinner could be particularly beneficial, although this specific activity was not investigated in the study. The results could be relevant for general exercise recommendations, as they suggest that exercise should not only be promoted in general but also better distributed strategically.
Possible Limitations
As this is a cross-sectional study, no clear causal relationships can be derived. In addition, the exact type of exercise was not recorded, and no distinction was made between leisure and work activity, so it is not clear whether it was voluntary or work-related. The participants’ diet was also not taken into account, although it can influence the metabolism.
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Conclusion
The study shows that the time of day is a factor in reducing the risk of obesity and diabetes and that exercise in the afternoon and evening appears to be the most effective. Anyone wishing to promote their health in a targeted manner could, therefore, benefit from scheduling exercise for the second half of the day. At the same time, nocturnal activity should be avoided as it is associated with negative metabolic changes.