DAVIS, CALIFORNIA. A zinc deficiency has been linked to retarded growth, impaired immune function, and poor pregnancy outcome and infant health. A team of American and Mexican researchers now reports that the accurate determination of an individual's zinc status is difficult as zinc concentrations in blood samples vary significantly depending on when the blood sample is drawn (morning, afternoon or evening) and whether the patient had been fasting or not prior to the sampling. An elevated white blood cell count, the use of oral contraceptives, hormones or steroids, or the presence of diarrhea can also influence zinc levels as does age and gender. The researchers conclude that serum or plasma zinc level cannot be considered a reliable indicator of zinc status in an individual. For population studies they propose the following cutoff levels (in micrograms/dL) for zinc (levels below which a deficiency would be indicated):
Their cutoff points are based on data from the NHANES survey carried out among 14,770 participants
between 1976 and 1980.