Best Time of Day to Exercise for Lower Health Risks

Reference

Sabag A, Ahmadi MN, Francois ME, et al. Timing of moderate to vigorous physical activity, mortality, cardiovascular disease, and microvascular disease in adults with Obesity. Diabetes Care. 2024;47(5):890-897.

Study Objective

To determine if an association exists between the time of day when someone participates in moderate-to-vigorous physical activity (MVPA) and mortality, cardiovascular disease (CVD), and microvascular disease (MVD) in obese adults. Investigators also evaluated a subset of the study group with insulin-dependent diabetes (type 2 diabetes, T2D).

Design

Prospective, observational study

Participants

Investigators used data from 29,836 volunteers (53.2% female, 42.8% male, with a mean age of 62.2 ± 7.7 years) to evaluate all-cause mortality. 

Within the larger dataset, 24,660 volunteers had a diagnosis of cardiovascular disease (eg, myocardial infarction, hypertension, rheumatic fever with heart involvement, angina pectoris, pericarditis, valvular disease, myocarditis, etc), and 2,995 patients had been diagnosed with T2D.

Included in the microvascular disease analysis were 28,445 volunteers with ICD-10 diagnoses of neuropathy, nephropathy, or retinopathy.

Study Parameters Assessed         

Investigators assessed participants’ physical activity using an Axivity AX3 accelerometer (Axivity Ltd, Newcastle upon Tyne, UK) on their dominant wrist 24 hours per day for 7 days. They defined compliance as wearing the accelerometer for a minimum of 3 days for 16 hours or more per day. 

The researchers stratified activity into 4 levels and 4 intensities. 

The exercise levels were:

1. Sedentary. No movement.
2. Standing utilitarian movements. This includes activities such as ironing a shirt and washing dishes.
3. Walking, including “active commuting” and mopping floors.
4. Running/high-energy activities, which included active play with children.

The activity intensities included:

1. Sedentary
2. Light
3. Moderate
4. Vigorous

Walking activities were classified as light (an acceleration value of <100 milligravity [mG]), moderate (≥100 mG), or vigorous (≥400 mG) intensity. One mG is ¹/₁₀₀₀ of a G, which is the average acceleration of Earth’s gravity. Therefore, <100 mG is a force equal to <100 x 10^-3 meters/second. 

The timing of physical activity was based on when the majority of MVPA occurred and lasted 3 or more minutes. Timing categories were:

1. Morning (6 AM to before 12 PM)
2. Afternoon (12 PM to before 6 PM)
3. Evening (6 PM to before 12 AM)

Primary outcome measures  

Investigators obtained mortality data from the National Health Service database.

Key Findings

The average follow-up time was 7.9 years (±0.8 years). During this time, there were 1,425 deaths, 3,980 CVD events, and 2,162 MVD events.

All-cause mortality

MVPA in the evening was associated with the lowest mortality risk (hazard ratio [HR] 0.39; 95% CI 0.27, 0.55), while mortality risks were similar for those partaking in MVPA in the morning (HR 0.67; 95% CI 0.56, 0.79) and afternoon (HR 0.60; 95% CI 0.51, 0.71) MVPA.

In the subgroup analyses, evening MVPA was also associated with the lowest mortality risk in patients with obesity and T2D (HR 0.24; 95% CI 0.08, 0.76), followed by afternoon MVPA (HR 0.44; 95% CI 0.28, 0.72). MVPA in the morning was not associated with a decrease in all-cause mortality in those with obesity and T2D (HR 0.86; 95% CI 0.57, 1.29).

CVD incidence

Evening MVPA
In obese patients and in patients with obesity and T2D, evening MVPA was associated with the lowest CVD incidence. In patients with obesity, evening MVPA was associated with a CVD incidence HR of 0.64 (95% CI 0.54, 0.75). In patients with obesity and T2D, evening MVPA was associated with a CVD incidence HR of 0.54 (95% CI 0.34, 0.86).

Morning and Afternoon MVPA
In obese patients, no significant differences were noted in hazard ratios for CVD incidence in those reporting morning or afternoon MVPA. Morning MVPA was associated with a CVD incidence HR of 0.83 (95% CI 0.76, 0.91). Similarly, afternoon MVPA was associated with a CVD incidence HR of 0.85 (95% CI 0.77, 0.91).

In volunteers with obesity and T2D, morning MVPA was associated with a CVD HR of 0.73 (95% CI 0.56, 0.94), while afternoon MVP showed no significant association with CVD incidence (HR 0.85; 95% CI 0.69, 1.06).

MVD incidence

The magnitude of the association across the different time periods for the incidence of nephropathy, neuropathy, and retinopathy in adults with obesity was similar across the groups. Morning, afternoon, and evening MVPA groups had HRs of 0.79 (95% CI 0.70, 0.89), 0.84 (95% CI 0.75, 0.93), and 0.76 (95% CI 0.63, 0.92), respectively.

For people with obesity and T2D, evening MVPA had the greatest association, with an HR of 0.52 (95% CI 0.32, 0.86). In contrast, morning and afternoon MVPA had no or smaller associations. Morning MVPA was not significantly associated with MVD incidence (HR 0.89; 95% CI 0.69, 1.14), while the association with MVD in the afternoon MVPA group was 0.75 (95% CI 0.59, 0.95).

Practice Implications

This is the first prospective study to evaluate the association between clinical outcomes (eg, all-cause mortality, incident CVD, and incident MVD) and the time of day when someone exercises. 

While evening MVPA was associated with the greatest reduction in all-cause mortality and CVD in patients with obesity and those with obesity and type 2 diabetes, it should be noted that morning exercise and afternoon exercise were also associated with lower all-cause mortality in this group, though the magnitude of the benefit was statistically less. 

Similarly, exercising during any time period (vs no aerobic bouts) was associated with decreased MVD incidence. 

The results of this clinical trial imply that if patients can consistently exercise in the evening (after 6 PM), it is associated with the greatest health benefits.

The results of this clinical trial imply that if patients can consistently exercise in the evening (after 6 PM), it is associated with the greatest health benefits. 

Counseling patients to exercise is important; however, it’s also important to meet patients where they’re at. Not everyone can consistently exercise in the evening. If a patient cannot consistently exercise in the evening, exercising at any time of day should still be encouraged.

All previous studies that have evaluated exercise intensity and timing were retrospective analyses with significant heterogeneities in inclusion criteria and how MVPA and exercise time periods were defined. Additionally, how long someone had to exercise to be included in the dataset varied between studies, making it difficult to compare the findings from previous studies to this study under review. In the current study, an aerobic bout of exercise was defined as only 3 minutes or more and included activities such as playing with children. It is possible, due to the observational design and use of the accelerometer, that people who have the energy to be active in the evening have less CVD, MVD, and all-cause mortality. Those who were tired from their day could have been more sedentary, which could indicate baseline health problems that could skew the data. 

One prior study that extracted data from the National Health and Nutrition Examination Survey (NHANES) found no association with all-cause mortality and exercising during the morning (before 1:00 PM) or evening (after 1:00 PM), with an HR of 1.08 (95% CI, 0.78 to 1.5, P=0.63).¹ While the volunteers had type 2 diabetes, as in the current clinical trial, they were not obese, and it was a retrospective study, used a different accelerometer (AM-7164, ActiGraph, Walton Beach, FL), required volunteers to wear the accelerometer for a different amount of time to be included in the dataset, and only stratified the exercise times into 2 categories: morning and evening.

A previous study in cancer patients, however, supports the association of the differential effects exercise timing has on some clinical outcomes. In a retrospective analysis of data from 233 cancer survivors (40.8% breast cancer, 10.7% prostate cancer, and 6.4% endometrial cancer), researchers collected data from 2016 to 2019 from the Huntsman Cancer Institute’s on-site exercise oncology program.² The average age of participants was 61.6 ± 13.2 years, and the average body mass index (BMI) was 28.3 ± 6.5 kg/m². Unlike the prospective study, this one did not evaluate exercise intensity and only broke the day into 2 time periods, AM (8:00 AM to 11:59 AM) and PM (noon to 3:00 PM).

Outcomes of this study included cardiorespiratory fitness measured by relative peak aerobic capacity (peak VO₂) and peak metabolic equivalents (METs); whole-body muscular endurance measured by 10 repetition maximum (10 RM) testing for chest press, latissimus pulldown, and leg press; physical function and strength measured by the timed up-and-go test, 30-second chair-stand test, and handgrip-strength test; anthropometrics including waist and hip circumference measurements; and fatigue and quality of life.

Overall, no significant association was found between the time of day one exercised and improvement in human performance and physical function. However, in a subset analysis of breast cancer patients, PM exercise was associated with improved cardiorespiratory fitness, lower-body muscular endurance, and lower-body physical function. As with the current study, the significant inverse association with PM exercise and health outcomes could be a sign of better vitality (having more energy at later hours) due to better baseline cardiorespiratory fitness. 

Further prospective, randomized clinical trials should be conducted to remedy the confounder inherent in self-selected movement time and activity.