| read through the study - seems to be quite a well done study.
Essentially what they found was that plasma vitamin C was lower in those with diabetes. They also found that vitamin C was lower in those with undiagnosed diabetes but an HbA1C of greater than 7% - which eliminates treatment of diabetes as a cause of the lower vitamin C.
They then went on and did a linear regression analysis of the data, and showed that Vitamin C levels were related to HbA1C levels - rising HbA1C meant lower vitamin C levels. It shows that there is a relationship between HbA1c and vitamin C.
The study was done because it has been noted that people with diabetes have lower vitamin C levels, and they wanted to confirm that this was indeed the case. Previous studies were either too small, or were done on a highly selective population (i.e. sick people in hospital) and therefore subject to selection biases.
They discuss 2 possible mechanisms - low vitamin C levels are linked to a cause for type 2 diabetes, or vitamin C is used up combating the effects of diabetes (preventing harm caused by high levels of circulating glucose)
The study would have been better if they did not have to correct for age - age is a huge confounding factor, and older people have lower vitamin C levels than younger people. In the study group higher Hba1C's were also associated with older subjects too.
What the study does not show.
1) whether the difference in vitamin C is clinically significant.
and importantly...
2) whether vitamin C supplementation will make any difference to the progression of diabetes.
(studies like this that get picked up by the media often go on to draw such conclusions in the press releases even though the data from the study does NOT support such conclusions)  | 
