Glucose tolerance, 263 status

Adipocytes have vitamin D receptors, and there is evidence that vitamin D may act as a suppressor of adipocyte development (Kawada et al., 1996). It has been suggested that vitamin D inadequacy may be a factor in the development of the metabolic syndrome ( syndrome X, the combination of insulin resistance, hyperlipidemia, and atherosclerosis associated with abdominal obesity). Sunlight exposure, and hence vitamin D status, may be a factor in the difference in incidence of atherosclerosis and myocardial infarction between northern and southern European countries in addition to effects on adipocyte development, calcitriol also enhances insulin secretion through induction of calbindin-D (Section 3.3.7.1), and there is some evidence vitamin D supplements can improve glucose tolerance (Boucher, 1998). 

In patients with a normal nutritional status, alcohol often results in hyperglycaemia. Apart from an alcohol-induced increase in catecholamines and cortisol (or ACTH), the reason for this also seems to be a reduced sensitivity of insulin receptors (e.g. due to zinc deficiency) (s. p. 50) and/or a lower glucose tolerance factor, (s. p. 51) (s. tab. 28.2)... 

Although requirements for vitamins and trace elements are known in health (Table 30-1), the effects of illness on these requirements are poorly understood and quantified. However, it is now apparent that as an individual develops progressively more severe depletion in vitamin or trace element status, the person passes through a series of stages with biochemical or physiological consequences. The metabolic or physiological penalty of such suboptimal nutritional status is usually not clear, but the assumption remains that the suboptimal metabolism is likely to have detrimental effects (e.g., subclinical deficiency of folic acid is associated with an increase in serum homocysteine concentration, which is an independent risk factor for coronary artery disease—see Chapter 26). Similarly, subclinical deficiency of chromium may be associated with impaired glucose tolerance in certain types of diabetes. 

Because chromium potentiates the action of glucose, a poor chromium status might lead to impaired glucose tolerance and Type II diabetes (Anderson 1998). The prevalence of impaired glucose tolerance was 15.8% in adults aged 40-74 years in the Third National Health and Nutrition Examination Survey in the U.S. (Harris etal. 

Phenformin - The recent status of the mechanism of action of phenformin, has been thoroughly reviewed >. There have been additional reports on the anorexigenic effect, or lack thereof, and on the inhibitory effect of the drug on the rate of intestinal glucose absorption. Although phenformin increases the tolerance to orally administered glucose, it has no effect on intravenous glucose tolerance in hximans . 

Inorganic chromium is also carried in the blood by the protein albumin, whereas organically-bound chromium is carried in the blood as a component of the glucose tolerance factor. These forms of chromium do not appear to be affected by the iron nutritional status. 

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