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Letters |
1
Applied Research Institute, PO Box 1925, Palmerston North, New Zealand
2
Radiation Studies, Box 351650, University of Washington, Seattle, WA 98195
a Author for correspondence. Fax 64-6-353-1012;
cakrone{at}xtra.co.nz.
To the Editor:
Blood glucose (BG) concentrations averaged over a 2- to 3-month period are represented by blood glycohemoglobin (GHb) as a percentage of total hemoglobin. Strict glycemic control is important to the successful outcome of diabetic pregnancy and in avoiding development of many diabetic complications (1). Hyperglycemia in nondiabetics is a major risk factor in cardiovascular disease and cancer (2). Thus, knowledge of an individual’s true GHb value is vital. This need has prompted continuing investigations of potential interferences in GHb assays (3)(4), including conflicting reports on the effect of vitamin C on GHb (5)(6)(7).
As a part of our research on effects of dietary variables on tumor
growth, two groups of 18 mice each were provided either ascorbic acid
(AA; vitamin C) in drinking water (2.5 g/L) or unsupplemented
water. Blood glucose was measured six times during the 2-month study
(Glucometer; Bayer Diagnostics). We observed no differences in BG
between the groups. At the beginning of the study, baseline BG
concentrations (mean ± SD) for the non-AA and AA groups were
82 ± 16 and 79 ± 15 mg/100 mL, respectively. The BGs at the
end of the study were, respectively, 90 ± 16 and 87 ± 18
mg/100 mL. Also at the end of the study, GHb by affinity chromatography
(Glycotest; Pierce) was determined. For this variable, the AA
group exhibited a significantly lower value (i.e., GHb, 4.39% ±
0.78% for non-AA mice and 3.39% ± 0.60% for the AA-supplemented
mice; t = 4.324; P 
0.0001).
AA may lead to interferences in GHb assays, particularly in some based on charge separation (e.g., electrophoresis and ion exchange), where a positive interference has been observed (6). The affinity-chromatography method we used, however, was not affected. This suggests that the AA-associated decrease in GHb reflected a genuine in vivo decrease in glycation.
In 1988, Ely et al. (5) reported antagonism of hemoglobin
glycation by AA in animals and humans. Since then, two contradictory
reports of the effect of AA supplementation (750–1500 mg/day) on GHb
in humans have appeared (6)(7). Using affinity
chromatography, Davie et al. (6) found an 18%
decrease in GHb, whereas Weykamp et al. (7) found no
significant change. Our data show a 23% reduction in GHb in mice
consuming 
7.5 mg of AA/day. Thus, the important question of whether
GHb measurements accurately represent average BG in persons who take AA
supplements remains unanswered.
AA is the most commonly consumed nutritional supplement after multivitamins (8), and in the western United States, >11% of adults take an AA supplement daily. Laboratory, epidemiologic, and intervention studies suggest that antioxidant vitamins, especially AA, have long-term benefits in attenuating the progression of diabetic complications, and diabetics are encouraged to take AA. In light of these facts and the importance of BG in other aspects of human health, including immunity and aging, the uncertainty regarding the influence of AA on GHb demands further investigation.
Acknowledgments
This work was supported in part by the Northwest Oncology Foundation, Seattle, WA.
References
The following articles in journals at HighWire Press have cited this article:
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  C. A. Krone and J. T. A. Ely Controlling Hyperglycemia as an Adjunct to Cancer Therapy Integr Cancer Ther, March 1, 2005; 4(1): 25 - 31. [Abstract] [PDF]
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 J. T.A. Ely and C. A. Krone Aging: Predictions of a New Perspective on Old Data Experimental Biology and Medicine, December 1, 2002; 227(11): 939 - 942. [Full Text]
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