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Daily Variation in Plasma Zinc Concentrations in Women Fed Meals at Six-Hour Intervals^1,2,3,

Janet C. King⁴, K. Michael Hambidge^*, Jamie L. Westcott^*, Deborah L. Kern^* and Guillermo Marshall

Department of Nutritional Sciences, University of California, Berkeley, CA 94720 ^* Department of Pediatrics and Center for Human Nutrition, University of Colorado Health Sciences Center, Denver, CO 80262 Department of Preventive Medicine and Biometrics, University of Colorado Health Sciences Center, Denver, CO 80262

Ten pre-menopausal women participated in two studies to measure the daily variations in plasma zinc when meals were fed at 6-h intervals and to determine if the response was related to shifts in serum insulin, glucose, calcium, or phosphorus concentrations. In Study 1, identical meals were fed at 6-h intervals for 2 d, and blood was sampled 8 times between each meal. In Study 2, the women fasted from 1800 h on d 1 to noon the next day, and blood was sampled hourly from 0700–1200 on d 2. The postprandial plasma zinc response was similar following all four meals and accounted for 50% of the total within subject variation in plasma zinc. A small (2–6%) increase occurred within the first 60 min; then plasma zinc declined to a low point at 4 h after the meal. This characteristic pattern was not observed during the fasting study. Serum phosphorus varied consistently after each meal with a net efflux from circulation that preceded an efflux of zinc by 2 h. The postprandial response of serum glucose and insulin were related to the postprandial plasma zinc response measured 6 h earlier; the variables were not correlated at concurrent time points. The data show that food intake is a determinant of the daily variations in plasma zinc. The net efflux of zinc from circulation following meals may reflect hepatic zinc uptake in association with an increase in postprandial liver metabolism.

KEY WORDS: • zinc • phosphorus • humans • diurnal variation • postprandial response

¹ Presented in part at the 1990 Annual Meeting of the American Institute of Nutrition, April 1990 [King, J. C., Hambidge, K. M., Kern, D. L., English, J. L. & Marshall, G. (1990) Food consumption and the daily variation in plasma zinc in adult women. FASEB J. 4: A648. (abs.) and Hambidge, K. M., King, J. C., Kern, K. L., English, J. L. & Marshall, G. (1990) Postprandial changes in plasma zinc: Temporal relationship to hormonal and substrate changes. FASEB J. 4: A648 (abs.)].

² Supported in part by grants 5 RO1 DK12432 and 5 RO1 HD 23855 from the National Institutes of Health NIDDKD and the National Institutes of Health General Clinical Research Center grants RR00069 and RR00051.

³ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

⁴ To whom correspondence and reprint requests should be addressed.

Manuscript received 4 October 1993. Revision accepted 23 November 1993.