Appropriate timing of exercise for adults with obesity including those with type 2 diabetes

Diabetes, Obesity Metabolism (DOM) NOW–May 2024

It is well-recognized that exercise remains the cornerstone of management for people with type 2 diabetes and/or obese. In addition to support initiation and maintenance of weight loss and improvement in cardio-metabolic risk factors, engaging in regular moderate to vigorous physical activity have also been shown to contribute to improvement in cardio-metabolic risk factors, cardio-respiratory fitness, preservation of lean muscle mass as well as physical and mental well-being. While these maybe the case, there remains ongoing uncertainty with regards to whether morning, afternoon or evening timing may lead to greater improvements in cardio-metabolic outcomes. This is important since obesity and type 2 diabetes are associated with circadian misalignment and therefore impairment in metabolic processes. Previous RCT have reported that late-afternoon or evening aerobic exercise produce greater improvements in glycaemic outcomes but it is not known whether this translate to longer-term outcomes such as morbidity and mortality.

To answer this question, researchers analysed UK Biobank data of 29 836 participants with obesity (body mass index, › 30; mean age, 62.2 years; 53.2% women), including 2995 also diagnosed with T2D from a UK biobank accelerometry substudy.¹ Aerobic exercise was defined as bouts lasting ≥3 continuous minutes. Participants were categorized into morning (6 am–12 pm), afternoon (12 am–6 pm), or evening exercise (6 pm–12 am) based on when they undertook the majority of their aerobic exercise. The reference group included participants with an average of less than one aerobic exercise bout per day. Following adjustment for potential confounders, the association between the timing of aerobic physical activity and risk for all-cause mortality, CVD (defined as circulatory, such as hypertension), and microvascular complications (neuropathy, nephropathy, or retinopathy) was evaluated over a median follow-up of 7.9 years.

At follow-up, 1425 deaths, 3980 CVD events, and 2162 microvascular event occured. Compared with activity in the reference group, while afternoon and morning exercise produced lower mortality risk compared with reference group, evening exercise was associated with the lowest risk of mortality. The mortality risk was even lower in the type 2 diabetes subgroup. Similar patterns were observed for CVD and microvascular disease. Findings were similar in the Type 2 Diabetes subset.

This study therefore suggested that in addition to the total volume of exercise undertaken, its timing is also important in order to optimize cardiovascular, microvascular and mortality outcomes for people living with obesity or type 2 diabetes. Some limitation needs to be highlighted—this is an observational study with allocation and unadjusted confounding biases. In addition, participants from UK biobank may not be generalizable to the real world population. Nonetheless, I believe that evidence derived from this study should be included in updated national and international guidance for exercise. It is however important to recognize that undertaken regular and consistent exercise can be challenging and time consuming for many patients. As such, undertaking exercise should be encouraged first, irrespective of timing to suit patients' convenience. Thereafter, where appropriate, patients should be encouraged if possible to prioritize evening exercise.