People generally have a good understanding of what is healthy—standing is preferable to sitting, exercise is beneficial for overall health, and getting quality sleep is crucial. However, if exercising in the evening disrupts our sleep or makes us feel the need to be more sedentary to recover, an important question arises—what is the best way to manage our 24-hour day to optimize our health? Our research aimed to answer this for risk factors associated with heart disease, stroke, and diabetes. We discovered that the ideal amount of sleep was 8.3 hours, and for both light activity and moderate to vigorous activity, 2.2 hours was optimal. Current health guidelines advise engaging in 2.5–5 hours of moderate-to-vigorous-intensity physical activity per week.
However, growing evidence indicates that how you spend your day can significantly impact your health. This includes the time spent sitting, standing, engaging in light physical activity (like walking around your house or office), and sleeping, in addition to moderate-to vigorous-intensity physical activity. Our study involved more than 2,000 adults who wore sensors to monitor their physical behaviors over the span of seven days, which provided insight into how they typically spent 24 hours. At the beginning of the study, participants had their waist circumference, blood sugar, and insulin sensitivity measured.
The data from the sensors and assessments was analyzed against markers of health risks, such as a heart disease and stroke risk score, to develop a model. Through this model, we processed thousands of 24-hour variations to identify those with the lowest estimated associations with heart disease risk and blood-glucose levels. This resulted in many optimal combinations of sitting, standing, light, and moderate-intensity activity. When analyzing waist circumference, blood sugar, insulin sensitivity, and a heart disease and stroke risk score, we observed different optimal time ranges. Where these ranges overlapped was considered the optimal zone for heart disease and diabetes risk. We found that light-intensity physical activity (defined as walking less than 100 steps per minute)—like walking to the water cooler, bathroom, or leisurely strolling with friends—had strong connections with glucose control, particularly in people with type 2 diabetes.
This light-intensity physical activity is likely accumulated throughout the day rather than during a dedicated session of light exercise. Our experimental evidence indicates that regularly interrupting sitting with light physical activity (such as taking a 3–5 minute walk every hour) can enhance metabolism, especially after lunch. Although more than 2 hours a day may seem a significant amount for moderate-to-vigorous physical activity, we defined it as more than 100 steps per minute, equating to a brisk walk. It is important to remember that these findings are preliminary. This is the first study of heart disease and diabetes risk and the “optimal” 24 hours, and further confirmation through continued studies is needed.
The data is also cross-sectional, meaning the estimates of time use are correlated with disease risk factors, so it is unclear whether the way participants spent their time affects their risk factors or if those risk factors influence how they spend their time. Currently, Australia’s physical activity guidelines only recommend exercise intensity and duration. New guidelines are being developed to incorporate 24-hour movement.
Soon, Australians will be able to use these guidelines to assess their daily routines and identify areas for improvement. While our new research can help inform the upcoming guidelines, the recommendations should be viewed as a guiding principle: a benchmark to improve your health. Essentially, this involves reducing sitting time where possible, increasing standing and light-intensity physical activity, enhancing vigorous physical activity, and aiming for 7.5–9 hours of healthy sleep per night. Positive changes could include cutting down screen time in the evening, choosing an active commute over driving, or prioritizing an earlier bedtime instead of watching television late in the evening.