Zinc does not increase white blood cell circulation

BELFAST, Ireland

Zinc supplementation does not affect circulating levels of white blood cells, although it does not adversely affect immune status, according to researchers from Belfast City Hospital. Their study, printed in the May issue of the British Journal of Nutrition (89, 5:695-703, 2003) (www.nutritionsociety.org.uk/bjn), investigated the effects of chronic zinc supplementation on circulating levels of peripheral blood leukocytes (white blood cells that develop into two types of immune cells to provide natural and adaptive immunity) and lymphocyte subsets (white blood cells that make up the body's adaptive immune system).

Researchers randomly assigned 19 men to receive 30 mg/d of zinc and 19 men to receive placebo for 14 weeks. All men were given 3 mg/d of copper for an additional eight weeks to counteract any reduction in copper stores zinc supplementation may have caused, as copper deficiency could also affect immunity. Researchers estimated the men's dietary zinc intakes were approximately 10 mg/d, which was in addition to supplemental zinc.

An analysis of blood samples demonstrated zinc had no effect on circulating levels of peripheral blood leukocytes or on lymphocyte subsets. However, there appeared to be a seasonal variation in selected lymphocyte subsets in both the placebo and treatment groups, with alterations in the levels of B cells and T cells (two types of lymphocytes).

"Findings indicted no adverse effects of zinc supplementation on immune status or copper status and support the U.S. upper [intake] level of zinc tolerance of 40 mg/d," researchers concluded. "The seasonal variations observed in lymphocyte subsets in the group as a whole could have implications for seasonal variability in the incidence of infectious diseases."