Review: the effect of exercise on HbA1c in type 1 diabetes is still uncertain

Runners

Existing recommendations for exercise in diabetes are based largely on evidence from the general population or from people with type 2 diabetes.  This systematic review set out to look specifically at the effect of exercise on glycaemic control among people with type 1 diabetes.

Clinical question

In people with type 1 diabetes, does exercise improve glycaemic control?

Methods

This is a systematic review of prospective clinical trials.

A comprehensive literature search is reported, which was carried out in May 2012.  The reviewers made attempts to identify unpublished studies.

They included studies that:

  1. looked at people with type 1 diabetes
  2. undertaking supervised or unsupervised exercise training interventions
  3. in comparison with no intervention, and
  4. reported HbA1c outcomes.

Non-randomised trials were included.

ExercisingResults

They found 13 trials, of which 8 were randomised, comprising 452 participants.

Overall, the trials were rated as having a substantial risk of bias.  They were also found to have important differences in the types of participant, duration and mode of exercise training.

When they combined the data from all the different studies, the reviewers found no significant difference between exercise training and the control groups for HbA1c.  Meta-analysis estimated a reduction of −0.25% (95% CI, −0.59% to 0.09%).  No significant difference was found for hypoglycemia.

However, they found substantial heterogeneity in the results of the studies, suggesting that they were not consistent.

Comments

  • This looks like a good quality review of poor quality evidence.  A comprehensive search was carried out.  Study evaluation and data extraction were carried out by two blind, independent reviewers.  All the various subgroup and sensitivity analyses were planned in advance.  The reviewers did their best, but there just wasn’t enough data.
  • The reviewers do claim that these data show that exercise is safe, with no evidence of additional hypoglycaemia.  However there really isn’t enough data here to say this for certain.
  • Heterogeneity was a significant problem.  The exercise interventions may not have been similar enough to warrant merging.  Furthermore, they may not have been sustained for long enough.
  • A subgroup analysis indicated that longer interventions may have had more of an impact on HbA1c.  This might suggest that future research should focus on interventions that are long enough to have  a sustained effect.
  • The reviewers comment that the intensity of the exercise interventions and dietary activity were inadequately reported in the trials.
  • Adjustment of insulin may account for lack of reduction in HbA1c.
  • Further high quality, large-scale randomised trials are warranted in any case.

Reference:

Kennedy A, Nirantharakumar K, Chimen M, Pang TT, Hemming K, Andrews RC, Narendran P. Does exercise improve glycaemic control in type 1 diabetes? A systematic review and meta-analysis PLoS ONE 2013; 8(3):e58861

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Badenoch

Badenoch
I am an information scientist with an interest in making knowledge from systematic research more accessible to people who need it. This means you. I've been attempting this in the area of Evidence-Based Health Care since 1995. So far the results have been mixed. For some reason we expected busy clinicians to search databases and appraise papers instead of seeing patients. We also expected publishers to make the research freely available to the people who paid for it.. Ha! Hence The National Elf service.

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