Aims/hypothesis
Patients with type 1 diabetes mellitus are more susceptible than healthy individuals to exercise-induced oxidative stress
and vascular endothelial dysfunction, which has important implications for the progression of disease. Thus, in the present
study, we designed a randomised double-blind, placebo-controlled trial to test the original hypothesis that oral prophylaxis
with vitamin C attenuates rest and exercise-induced free radical-mediated lipid peroxidation in type 1 diabetes mellitus.
Methods
All data were collected from hospitalised diabetic patients. The electron paramagnetic resonance spectroscopic detection of
spin-trapped α-phenyl-tert-butylnitrone (PBN) adducts was combined with the use of supporting markers of lipid peroxidation and non-enzymatic antioxidants
to assess exercise-induced oxidative stress in male patients with type 1 diabetes (HbA1c 7.9 ± 1%, n = 12) and healthy controls (HbA1c 4.6 ± 0.5%, n = 14). Following participant randomisation using numbers in a sealed envelope, venous blood samples were obtained at rest,
after a maximal exercise challenge and before and 2 h after oral ingestion of 1 g ascorbate or placebo. Participants and lead
investigators were blinded to the administration of either placebo or ascorbate treatments. Primary outcome was the difference
in changes in free radicals following ascorbate ingestion.
Results
Six diabetic patients and seven healthy control participants were randomised to each of the placebo and ascorbate groups.
Diabetic patients (
n = 12) exhibited an elevated concentration of PBN adducts (
p < 0.05 vs healthy,
n = 14), which were confirmed as secondary, lipid-derived oxygen-centred alkoxyl (RO·) radicals (a
nitrogen = 1.37 mT and aβ
hydrogen = 0.18 mT). Lipid hydroperoxides were also selectively elevated and associated with a depression of retinol and lycopene
(
p < 0.05 vs healthy). Vitamin C supplementation increased plasma vitamin C concentration to a similar degree in both groups
(
p < 0.05 vs pre-supplementation) and attenuated the exercise-induced oxidative stress response (
p < 0.05 vs healthy).
There were no selective treatment differences between groups in the primary outcome variable.
Conclusions/interpretation
These findings are the first to suggest that oral vitamin C supplementation provides an effective prophylaxis against exercise-induced
free radical-mediated lipid peroxidation in human diabetic blood.
Clinical trials registration number: ISRCTN96164937
Funding: No external funding.
Keywords Ascorbic acid - Electron paramagnetic resonance - Free radicals - Glucose - Type 1 diabetes mellitus