Among other things, a subclinical zinc deficiency in humans has been attributed to increased levels of inflammation markers and reduced immunocompetence. (sciencedaily.com)
[Jean - Nicolas Audet et al., The town bird and the country bird: problem solving and immunocompetence vary with urbanization (scientificamerican.com)
An implicit assumption of this hypothesis is that males that can afford to produce more elaborate carotenoid - dependent displays must be healthier individuals with superior immunocompetence. (science.sciencemag.org)