NHS Evidence Health Information Resources formerly National Library for Health

On 8th August 2007 three newspapers reported that a lack of vitamin B1 has been linked to vascular disease in people with diabetes. The newspapers reflected the conclusions of a case-control study, however, given the prevalence of diabetes, this was a small study on which to base such strong conclusions.

On 8th August 2007, three newspapers (1-3) reported that a lack of vitamin B1 has been linked to vascular disease in people with diabetes.
The research, published in Diabetologia (4), was a small case-control study involving 94 people (26 type 1 diabetes; 48 type 2 diabetes; 20 controls). Plasma thiamine levels were 76% lower in people with type 1 diabetes, and 75% lower in people with type 2 diabetes compared to controls. Urinary excretion, renal clearance and fractional excretion of thiamine were all substantially increased in those with diabetes.
The newspaper reports generally provided an accurate overview of the results of the study. The Daily Express (3) reported a 75% decrease in the risk of kidney problems with a thiamine supplement 300 times greater than that naturally derived from the diet; these data were not presented in the study. The study involved 94 people and given the prevalence of type 1 and 2 diabetes, this was a small number of people on which to base such strong conclusions.

Evaluation of the evidence base for low plasma thiamine concentrations in diabetics as a marker of vascular disease.

Where does the evidence come from?

The study was conducted by Dr Thornalley and colleagues from the Department of Biological sciences, University of Essex, Colchester, UK; the Clinical Sciences Research Institute, University of Warwick, Coventry; the Colchester General Hospital, Colchester; and the Ipswich Diabetic Foot Unit and Diabetes Centre, Ipswich Hospital NHS Trust, Ipswich, UK. The project was funded by Diabetes UK.

What were the authors' objectives?

To assess thiamine status of people with type 1 and 2 diabetes and the link to vascular dysfunction.

What was the nature of the evidence?

This was a case-control study of 94 people; 26 had type 1 diabetes, 48 had type 2 diabetes, and 20 were healthy controls. Diabetic patients were recruited from one diabetic clinic. To be included, diabetic patients had to be excreting no more than 300mg of albumen in the urine over 24 hours, be between 18 and 65 years of age, have had diabetes for at least 5 years, a glycated haemoglobin level of less than 10%, and a body mass index between 19 and 40 kg/m2. Controls were partners and friends of the participants and investigators. Participants were matched for age and gender. Assays of thiamine and phosphorylated metabolites were conducted, along with a range of other biochemical measurements.

How did participants differ on their levels of exposure to the factor of interest?

The authors stated that participants were matched on age and gender; the mean age was 53 for controls, 48 for people with type 1 diabetes, and 62 for people with type 2 diabetes; the proportion of males was 50% for controls, 38% for people with type 1 diabetes, and 60% for people with type 2 diabetes. People with type 2 diabetes had a significantly shorter duration of disease than people with type 1 diabetes. As expected, people with diabetes had significantly higher fasting plasma glucose levels and glycated haemoglobin levels than controls.

What were the findings?

Plasma thiamine levels were 76% lower in people with type 1 diabetes, and 75% lower in people with type 2 diabetes compared to controls (Type 1 diabetes: 15.3 nmol/l SD 9.60; Type 2 diabetes: 16.3 nmol/l SD 11.5; Controls: 64.1 nmol/l SD 12.0).

Urinary excretion of thiamine was increased fourfold, renal clearance 24-fold, and fractional excretion 25-fold in people with type 1 diabetes compared to controls. In people with type 2 diabetes, urinary excretion was increased threefold, renal clearance 16-fold, and fractional excretion 15-fold compared to controls. Further biochemical results were reported.

Using Spearman's Rank correlation, the only significant correlations between metabolic control and vascular dysfunction were negative correlations between both plasma thiamine concentrations and urinary excretion of thiamine, with plasma soluble vascular adhesion molecule-1, a marker of endothelial dysfunction.

What were the authors' conclusions?

Low plasma thiamine concentration is prevalent in patients with type 1 and type 2 diabetes, associated with increased thiamine clearance. The deficiency of thiamine in clinical diabetes may increase the fragility of vascular cells to the adverse effects of hyperglycaemia and thus increase the risk of developing microvascular complications.

How reliable are the conclusions?

This was a small case-control study with clearly defined inclusion criteria. Although the authors stated that matching of participants was undertaken, there does seem to be some dissimilarities at baseline. It is unclear whether those performing and interpreting the tests were blind to disease status. Given the prevalence of type 1 and 2 diabetes, this was a small number of people on which to base such strong conclusions.

Systematic reviews

Information staff at CRD searched for systematic reviews relevant to this topic. Systematic reviews are valuable sources of evidence as they locate, appraise and synthesize all available evidence on a particular topic.

There were no related systematic reviews identified on the Cochrane Database of Systematic Reviews (CDSR) or on the Database of Abstracts of Reviews of Effects (DARE).