Sievenpiper: Thermometer rising [CMAJ

Thermometer rising

CMAJ 2000;163(4):387

In response to: S.C. Arya

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We agree with Subhash Arya that ambient temperature during an oral glucose tolerance test might be another important determinant of outcome. However, the findings of Schmidt and coworkers,¹ which form the basis of this suggestion, are complicated by several factors. Their analysis involved pregnant subjects, was observational (temperature was measured, not controlled) and did not differentiate between the effects of acute and chronic ambient temperature. Three earlier studies that investigated differences in blood glucose levels at 2 clinically controlled temperatures (23°C v. 33°C) in nonpregnant subjects are more directly applicable.^2,3,4 All 3 support the findings of Schmidt and coworkers,¹ demonstrating that an increase in ambient temperature increases 2-h plasma glucose levels after a 75-g oral glucose tolerance test.

To avoid the possibility that changes in ambient temperature might confound our results, the temperature is controlled in our clinic by a thermostat set at 22°C and subjects acclimatize for a minimum of 15 minutes before commencing testing. The blood glucose raising effect of dilution we observed at 30, 45 and 60 minutes and for the area under the curve, therefore, is relevant for this temperature [Research].⁵ Whether our observations at 22°C would hold at higher or lower temperatures is unclear. Temperature should not interact with the effect of dilution, provided the temperature is constant for each dilution. There is no direct evidence to suggest that the gastric-emptying mechanism, by which dilution is thought to increase glycemia, is influenced by ambient temperature within normal testing limits, although cold stress might affect gastric emptying.⁶

It would be interesting to explore the interaction between the effects of temperature and dilution on postprandial glycemia in a further study, but such a study likely would not yield practical results. It is probably sufficient to be aware that both of these factors affect the outcome of oral glucose tolerance testing. In this regard, attempts might be considered to standardize ambient temperature and account for its effects when comparing across centres. The same might be considered for dilution when using oral glucose tolerance testing criteria that rely on intermediate time points for diagnosis, as these points, but not 2-h postprandial glucose levels, appear to be sensitive to alterations in dilution.⁵

John L. Sievenpiper
Vladimir Vuksan
Department of Nutritional Sciences
Faculty of Medicine
University of Toronto
Toronto, Ont.

References

    1.    Schmidt MI, Matos MC, Branchtein L, Reichelt AJ, Mengue SS, Iochida LC, Duncan BB. Variation in glucose tolerance with ambient temperature. Lancet 1994;344:1054-5. [MEDLINE]

    2.    Frayn KN, Whyte PL, Benson HA, Earl DJ, Smith HA. Changes in forearm blood flow at elevated ambient temperature and their role in the apparent impairment of glucose tolerance. Clin Sci 1989;76:323-8. [MEDLINE]

    3.    Akanji AO, Bruce M, Frayn K, Hockaday TD, Kaddaha GM. Oral glucose tolerance and ambient temperature in non-diabetic subjects. Diabetologia 1987;30:431-3. [MEDLINE]

    4.    Akanji AO, Oputa RN. The effect of ambient temperature on glucose tolerance. Diabet Med 1991;8:946-8. [MEDLINE]

    5.    Sievenpiper JL, Jenkins DJ, Josse RG, Vuksan V. Dilution of the 75-g oral glucose tolerance test increases postprandial glycemia: implications for diagnostic criteria. CMAJ 2000;162(7):993-6.

    6.    Fone DR, Horowitz M, Maddox A, Akkermans LM, Read NW, Dent J. Gastroduodenal motility during the delayed gastric emptying induced by cold stress. Gastroenterology 1990;98:1155-61. [MEDLINE]