SELECT MICRONUTRIENTS IN DIABETES MANAGEMENT
The trace element trivalent chromium (Cr+3) is required for the maintenance of normal glucose metabolism. Experimental chromium deficiency leads to impaired glucose tolerance, which improves upon the addition of chromium to the diet.5Because there is no accurate biochemical indicator of chromium status, the determination of clinical chromium deficiency is difficult.2,5 Effects of chromium on glycemic control, dyslipidemia, weight loss, body composition, and bone density have all been studied.4,5
The current AI for chromium is 25 μg for women and 35 μg for men. No UL has been established. Previous recommendations placed a daily intake of ≤200 μg/day within a safe and adequate range. Usual dietary intakes in the United States are estimated to range between 20 and 30 μg/day.5
There is no evidence that people with diabetes have increased rates of deficiency, although several risk factors for micronutrient deficiencies are common in people with diabetes. These include hyperglycemia and glycosuria, low-calorie diets, and increased age. Other factors that may increase chromium requirements include pregnancy, lactation, stress, infection, physical trauma, and chronic vigorous exercise.4,5 Because chromium is a nutrient, supplements will only benefit individuals who have a deficiency.
Mechanism of action.
Chromium appears to act by enhancing or potentiating insulin’s actions.6 No chromium-containing enzyme has been discovered, and the biologically active form of chromium is still uncertain. Chromium’s actions have been attributed to an increase in the number of insulin receptors,5 increased binding of insulin to the insulin receptor, and increased activation of the insulin receptor in the presence of insulin.6 In vitro studies using organic forms of chromium have documented altered activity of phosphotyrosine phosphatase and phosphotyrosine kinase.5,6
Numerous researchers have investigated the effects of chromium supplements on glycemic control in type 2 diabetes,7–13 type 1 diabetes,8 gestational diabetes,14insulin resistance,15 reactive hypoglycemia,16 the elderly,17 and steroid-induced diabetes.18 Chromium has also been shown to improve various aspects of dyslipidemia in diabetic subjects.7,9,10 There are few well-controlled, well-designed studies.
The most definitive support for chromium supplementation in type 2 diabetes was provided by a 1997 randomized, double-blind, placebo-controlled study conducted in China by Anderson et al.7 One hundred and eighty subjects were randomized to placebo, 200 μg/chromium picolinate/day, or 1,000 μg chromium picolinate/day for 4 months. HbA1c significantly declined in both groups at 4 months compared to placebo (P <0.05) (placebo 8.5%, 200 μg 7.5%, 1,000 μg 6.6%). Fasting blood glucose (FBG) levels, 2-h oral glucose tolerance test, and insulin and cholesterol levels all decreased in the high-dose-supplement group at 4 months.
The dose-dependent response and clinically significant decreases in HbA1c(decreases are similar in magnitude to those seen with many oral hypoglycemic agents) seen in this study are encouraging, although questions remain about its applicability in the United States, where ethnicity, dietary chromium intakes, and average body mass index of people with diabetes differ from those of the Chinese subjects.
Overall, the results of research studies are mixed,5 with some showing positive effects7,8,10–14 and others having clearly negative or ambiguous results.9,10,16,18 Studies using higher doses7,11,12 and more bioavailable forms of chromium7,8,11–13 have had more positive effects than those using other forms of chromium.10,16,18 Studies in which subjects were possibly consuming low-chromium diets or had other risk factors for deficiency were also more likely to show positive effects.7,11,13,14
Research on chromium is summarized in Table 1. When evaluating these studies, one must pay particular attention to the form and dose of chromium used; the etiology of diabetes in the population studied; subjects’ duration of diabetes, ethnicity, and weight; study duration; subjects’ relative glycemic control; statistical and clinical relevance of the data; and the study design (with randomized, double-blind, placebo-controlled studies that control for dietary intake preferred). Emphasis should be placed on studies conducted after 1980, when methodological limitations in measuring chromium were resolved.