The authors concluded that there was no good evidence that oral vanadium supplementation improved glycaemic control in diabetes and so the routine use of vanadium could not be recommended; further research was required. This was a well-conducted review with a comprehensive search and the authors’ conclusions are likely to be reliable.

To evaluate the effectiveness of oral vanadium supplementation for glycaemic control in patients with type 2 diabetes mellitus.

MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials (CENTRAL), Cochrane Database of Systematic Reviews, Science Citation Index, CINAHL, AMED, International Bibliographic Info Dietary Supplements, ISI Proceedings, BIOSIS Previews, The National Research Register, Conference Papers index, Clinical Trials Register and Current Controlled Trials were searched to November 2007. Search terms were reported. No language restrictions were applied. Reference lists were screened and experts, authors and manufacturers were contacted.

Initially, controlled clinical trials were eligible if they evaluated the effects of oral vanadyl sulphate (30mg to 150mg daily for at least two months) on glycaemic control (glycated haemoglobin (HbA1c) and fasting blood glucose) in patients with type 2 diabetes mellitus. Studies had to have at least 10 adults in each treatment arm. Studies could be placebo-controlled randomised controlled trials (RCTs) or quasi-RCTs with or without a placebo control group. Subsequently, any clinical trial that evaluated 30mg to 150mg oral vanadium daily in patients with diabetes was sought.

The included within-patients studies evaluated oral vanadyl sulphate from 50mg to 300mg daily. Most studies included a run-in period from one to six weeks. Active treatment periods ranged from three to six weeks. Most of the included studies were in diabetic patients; two included non-diabetic patients. Duration of follow-up ranged from none to six weeks post-treatment.

Two reviewers independently selected studies.

The intention was that tTwo reviewers independently assess validity using sampling method, randomisation, allocation concealment, blinding, identical treatment of groups, intention-to-treat analysis and reporting of withdrawals, drop-outs and losses.

Two reviewers independently extracted data.

The intention was to use meta-analysis if studies were sufficiently homogeneous. In the absence of homogeneous good-quality trials, lesser-quality studies were combined in a narrative synthesis.

No RCTs or quasi-RCTs were identified that met the strict initial inclusion criteria.

The search identified five clinical within-patient trials of oral vanadium supplementation in adults with diabetes (n=48 patients with diabetes).

Four studies reported a significant reduction in HbAIc from baseline associated with at least one dose of vanadium. Five studies reported a significant reduction in fasting blood glucose from baseline associated with at least one dose of vanadium. No serious morbidities were reported, but all studies reported high rates of gastrointestinal side effects.

There was no good evidence that oral vanadium supplementation improved glycaemic control in patients with diabetes and so the routine use of vanadium could not be recommended. Further research was required.

The review question was clearly stated and inclusion criteria were specified. The search was comprehensive and included attempts to minimise publication and language biases. Appropriate methods were used to minimise reviewer error and bias during the review process. Validity was to be assessed using relevant criteria. Combining the lesser-quality studies in a narrative synthesis that took account of methodological limitations was appropriate.

This was a well-conducted review with a comprehensive search and the authors’ conclusions are likely to be reliable.

Practice: The authors stated that routine vanadium supplementation could not be recommended as treatment for patients with diabetes as its effectiveness was unknown and it had side effects.

Research: The authors stated that an adequately powered RCT was required to evaluate the effectiveness of oral vanadium supplementation in patients with diabetes. Future studies needed to have a minimum duration of three months to detect changes in HbA1c.

Royal College of General Practitioners Science Foundation.

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.