Systematic review shows more studies needed on psychological effects of exercise for type 2 diabetes

In the UK alone it’s estimated over two million adults have type 2 diabetes. That clearly warrants some serious research into its prevention and treatment, including the valuable role of exercise. We also know the effects of diabetes are not confined to physical problems, linked as it is to reduced quality of life as well as increased symptoms of anxiety and depression- something we’ve covered at Mental Elf before.

With exercise programmes showing promise in all three of these domains in systematic reviews in both healthy and clinical samples, and with no review currently existint that looks specifically at type 2 diabetes yet, it doesn’t take a professor of medical and clinical psychology to see the gap in the research literature. Or perhaps it does…

Researchers from Tilburg university, The Netherlands, sought to plug this hole by conducting a systematic review of existing randomised controlled trials (RCTs) that investigated the effects of exercise training on quality of life, emotional well-being and symptoms of anxiety and depression.

Published in March this year, the authors found too much heterogeneity between the studies to pool data for a meta-analysis. Reinterpreting the data from various studies, the reviewers found a mixed bag of results, and hence point to the obvious yet necessary conclusion: more high-quality RCTs are needed to gain greater clarity on the psychological effects of exercise training for people with type 2 diabetes.

Methods

The authors carried out a comprehensive literature search, selecting 20 RCTs with a total of 1,719 participants, with sample sizes ranging from 18 to 606.

Studies were included in the systematic review if they:

reported on exercise programmes lasting at least 4 weeks
used a control group involving usual care, sham exercise or an education programme
investigated exercise training as the sole intervention.

Owing to the variability in exercise programmes adopted, these were split into three categories:

aerobic training
resistance/strength training
combination of both

Measures used varied between studies, although the following were used in multiple studies:

Short-Form Health Survey (quality of life scale)
Center for Epidemiological Depression Scale (CES-D)
General Well-being Questionnaire (emotional well-being)
…Health and safety regulations presumably didn’t allow for one-handed barbell lifting (nor cape-wearing)

Standard mean differences (SMDs) were calculated wherever possible from the raw data provided. A SMD of 0.2 was considered to show a small effect, 0.5 moderate and 0.8 large. Positive SMDs reflected better outcomes in the various psychological domains.

Results

Here’s what they found:

Quality of life (10 studies):

Aerobic exercise (6 studies): Weak findings: Only one study showed positive findings for exercise group (subscales of satisfaction with physical health (p=0.03) and sleep (p=0.03)).
Resistance exercise (4 studies): Mixed results: Two studies found positive effects for exercise groups (p<0.001; SMD= 1.15 and p=0.02; SMD=0.87 in general health subscale); but one study showed a sign. effect in favour of control group (p<0.001; SMD= -0.38).
Combined exercise (10 studies): Mixed results: SMDs varying from -0.63 to 0.43; but largest study (n=606; 12 month intervention) showed positive results for exercise group (SMDs from 0.67 to 0.94 across subscales).

Depression (4 studies):

Weak findings: Only one study found positive effects for exercise group (p<0.001; SMD= 1.51), evaluating resistance training in ageing sample (mean age= 66).

Anxiety (1 study):

Aerobic training reduced anxiety symptoms compared with education group (p= 0.007; SMD= 0.66).

Emotional well-being (4 studies):

Mixed results: Two studies found positive effects of aerobic training on emotional well-being (p=<0.001; SMD= 2.26 and p=0.023; SMD= 0.69); one showed positive effect for resistance training (p<0.05; SMD= 1.33).

Conclusions

The authors concluded:

This first systematic review of the literature showed that the effects of exercise training on quality of life, symptoms of depression, symptoms of anxiety and emotional well-being in people with type 2 diabetes are conflicting; therefore, more research is warranted

Unfortunately no exercise programmes involved trampolines, which surely would score high on emotional well-being and quality of life

Unfortunately no exercise programmes involved trampolining, which surely would score high on emotional well-being and quality of life

Summary

Limitations:

There was massive variation between studies in terms of intervention type, measures used, risk of bias and sample population, making data pooling impossible and mixed results likely.
Most measures were taken immediately post-intervention, which may not have captured long-term effects, e.g. in quality of life.
Many of the studies had a relatively small sample size, resulting in minimal statistical power to detect significant outcome effects.
No efforts to check for publication bias were reported, highlighting the strong potential for missing studies that produced non-significant findings.

Despite the highly mixed results, encouragement can certainly be taken from the fact that the reviewers screened vigilantly for risk of bias across the selected studies and therefore those few studies that did reveal positive effects of exercise on quality of life, depression, anxiety and emotional well-being certainly justify the call for further high quality RCTs to be conducted in this highly important area of research.