A new study suggests that aerobic medium-to-vigorous physical activity benefits obese and diabetic people the most when conducted in the evening hours [1].
Do you really need morning runs?
Physical activity is an essential part of the longevity-conscious lifestyle and one of the best life-extending interventions currently available. However, questions remain as to what types of physical activity are the healthiest, in what quantities, and so on. Exercise is a heterogeneous universe, and finding an individual mix involves such factors as age, sex, and medical conditions.
Recently, the timing of physical activity has become a widely explored issue. There is still a widespread public misconception that to lead a healthy lifestyle means to get up at six in the morning and go for a run. Many people find this regimen too hard to maintain. Thankfully, the reality seems to be more lenient. Numerous studies have suggested that at least some types of exercise bring greater health benefits when performed in the afternoon and evening hours [2].
30,000 accelerometer-wearing participants
In this new study, Australian scientists utilized data from UK Biobank, a huge repository of longitudinal health data on about half a million British citizens. A subset of UKB participants wore sophisticated accelerometers for a week to register their physical activity patterns. The resulting data has spawned numerous enlightening studies.
These researchers wanted to determine the best timing of aerobic medium-to-vigorous physical activity (MVPI) in obese and diabetic people. They assessed such outcomes as mortality, cardiovascular disease, and microvascular disease.
While the researchers used their own sophisticated way to categorize physical activity, generally, medium physical activit is between 3 to 6 metabolic equivalents (METs), a scale in which 1 is energy consumption at rest and vigorous is everything north of 6. For instance, brisk walking falls into the medium category, while jogging is considered vigorous.
Aerobic MVPI was defined in this study as at least three continuous minutes of MVPI. The participants were divided into three groups according to when in the day most of their MVPI occurred: 6 AM to 12 PM for the morning group, 12 AM to 6 PM for the afternoon group, and 6 PM to 12 AM for the evening group.
Of about 30 thousand participants, all with body mass indices (BMIs) of more than 30, 2,995 had type 2 diabetes at baseline. The median age was 62, and gender distribution was fairly even. All results were controlled for potentially confounding factors, including non-health-related deaths, cholesterol levels, blood pressure, ethnicity, socioeconomic status, and the season of accelerometer wear time.
Go for a walk after work
The reference group included people who averaged less than one bout of aerobic MVPI per day. Compared to that group, all those who were more active showed less all-cause mortality. However, the evening exercisers stood out with a hazard ratio of 0.39: that is, they were almost three times less likely to die than non-exercisers. The reduction in mortality was less pronounced in the morning and afternoon groups (HRs of 0.67 and 0.60, respectively).
People diagnosed with type 2 diabetes seemed to benefit from evening exercise even more (HR of 0.24, which translates to more than a four-fold reduction in all-cause mortality). Afternoon MVPI also showed strong results in this subgroup (HR of 0.44). Interestingly, no statistically significant association was found for morning exercisers in this subgroup (HR of 0.86).
The results were largely similar for cardiovascular disease, with modest and almost similar reductions for the morning and afternoon groups (HR of 0.83 and 0.84 respectively), and a much larger one for the evening group (HR of 0.64). In the subset of diabetic participants, only evening exercise showed a statistically significant effect: HR of 0.54.
Different results were recorded for microvascular disease, which included nephropathy, neuropathy, and retinopathy. Here, all groups showed rather small effect sizes, although evening exercise still came out on top.
The frequency of aerobic bouts seemed to be more important for their association with health outcomes than the overall duration of daily activity. Concordantly, recent research suggests that short bouts of physical activity can have a strong health-promoting effect [3].
Populational studies like this one can only establish correlation and not causation, and their results can be affected by hard-to-eliminate confounding factors and arbitrary design decisions.
Building upon previous clinical studies, our analyses underscore the consistent association of evening MVPA with the lowest risk in mortality, as well as strong associations with the incidence of CVD and MVD, when compared with not undertaking aerobic MVPA bouts. These findings are robust and extend to the subset of participants with T2D, in whom evening MVPA exhibited even more pronounced associations with mortality and cardiovascular morbidity. Sensitivity analyses demonstrated that when controlling for more even temporal distributions of aerobic MVPA, evening MVPA was associated with the greatest reduction in mortality, whereas more evenly spread MVPA was associated with the greatest reduction in MVD incidence.
Literature
[1] Sabag, A., Ahmadi, M. N., Francois, M. E., Postnova, S., Cistulli, P. A., Fontana, L., & Stamatakis, E. (2024). Timing of Moderate to Vigorous Physical Activity, Mortality, Cardiovascular Disease, and Microvascular Disease in Adults With Obesity. Diabetes care, 47(5), 890-897.
[2] Moholdt, T., Parr, E. B., Devlin, B. L., Debik, J., Giskeødegård, G., & Hawley, J. A. (2021). The effect of morning vs evening exercise training on glycaemic control and serum metabolites in overweight/obese men: a randomised trial. Diabetologia, 64(9), 2061-2076.
[3] Stamatakis, E., Ahmadi, M. N., Gill, J. M., Thøgersen-Ntoumani, C., Gibala, M. J., Doherty, A., & Hamer, M. (2022). Association of wearable device-measured vigorous intermittent lifestyle physical activity with mortality. Nature Medicine, 1-9.
