Title: The Anderson study of glucose and insulin variables in type 2 diabetes following chromium supplementation
Key words: chromium supplementation, supplements, glucose, insulin, glucose metabolism, chromium picolinate, type II diabetes, Chinese, chromium deficiency, fasting blood glucose, 2-hour glucose tolerance, post-prandial, cholesterol, glycaemic control, †
Date: Sept 2006
Author: Morgan, G
The Anderson study of glucose and insulin variables in type 2 diabetes following chromium supplementation
The Anderson study (Anderson 1997) on the effect of chromium. supplementation on the biomarkers of type 2 diabetes is important, being the largest single double-blinded randomly controlled trial of the effect of this element on the glucose metabolism of this disorder. Previous trials had largely been with healthy non-diabetic subjects and had been underpowered, leading to negative conclusions (Althuis 2002). The Anderson study was a well designed and powered study that concluded that chromium, in the form of picolinate, led to improvements in glycaemic control in type 2 diabetics, an effect that was both significant and dose dependent.
The Anderson study has been criticized for its selectivity (the use of a Chinese cohort) and for its failure to address the problems of chromium status and replenishment in a clinical setting (Hellerstein 1998). Though the essentiality of chromium has been established from rat experiments (Mertz 1969) and total parenteral nutrition-induced deficiency (Jeejeebhoy 1977), nonetheless it remains the case that there are still no accepted parameters of chromium status (Stoecker 2001). The recommended daily intake (RDI) of chromium has been put at 35 mcg a day for an adult (National Academy of Sciences 2001) but it remains undetermined whether the 200 mcg and 1000 mcgs/day given to the two treatment groups in the Anderson study owed their efficacy to correction of an underlying chromium deficiency or through a pharmacological effect. Lack of dietary, genetic, and lifestyle information on the sample Chinese population, as well as variability in the absorption, utilization and excretion of chromium in diabetic and non-diabetic populations (do Canto 1995), and the instrumentation to determine these values, rendered it impossible to determine the cohortís exact chromium status.
The selective nature of the study group is compounded by their low BMI (22-23) and the possible interference effect of Chinese herbal remedies used by many of the participants, in addition to their regular oral hypoglycaemic agents. Differences in methodologies, such as the exclusion criteria used and questions of bias, also need to be addressed before the results could be extrapolated to a Western population. An improvement in the diabetic markers measured over the 4 month trial period, even in the placebo group, may reflect some of these factors.
Against these criticisms, the Anderson study has many positive points. The control and two test groups were well matched and the numbers (n=157) sufficient to generate a suitably powered study. The study was not designed to assess chromium status and the effects of correcting a chromium deficiency on the altered biochemical markers of type 2 diabetics, but rather the effect of an optimal and supra-optimal supplemental programme on these parameters.
At the two levels of supplementation (200 and 1000 mcg/day) the study was able to show significant reductions in the levels of HbA1c, fasting blood glucose, 2 hour glucose tolerance, and fasting and 2 hour post-prandial insulin. The greater improvements seen in the high chromium supplementation group argue for chromium exerting its effect on glucose metabolism through pharmacological or optimal nutritional pathways rather than through any deficiency or replenishment effect. The changes seen were progressive from month 2 to month 4 of the trial and were clinically significant, e.g. the HbA1c level dropped from 8.5 to 6.6% in the 1000 mcg/day group at 4 months. Supplemental improvements in total cholesterol levels also reinforced the conclusion of the essentiality of chromium in the metabolism of type 2 diabetes and in its treatment.
In conclusion, the Anderson study was a well designed double-blind placebo controlled trial that showed significant improvements in glycaemic control in type 2 diabetics with higher levels of chromium supplementation. An imperfect knowledge of the pharmacokinetics of the element chromium and imprecision in the definition and measurement of chromium status, though limiting the data extractable from the trial, does not invalidate the conclusions to be drawn from the study. As a corollary, however, precisely the inability of the study to quantify chromium status restricts any analysis of genetic, dietary and lifestyle factors that may have an effect on the biochemical parameters of type 2 diabetes. It is therefore true that it is difficult to extrapolate the findings of the Anderson study to a Western population. Whilst accepting this proviso, such well designed studies are indicated in a Western setting to help resolve some of the issues raised by the study, especially in view of the increasing commercial interest in chromium supplementation for this condition, much of it stemming from the Anderson study.
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