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Abstract
Objectives
This paper reviews evidence of an association between zinc (Zn) nutrition and Alzheimer's disease (AD) or age-associated cognitive decline. The involvement of zinc in the pathology of AD has been reported hundreds of times. It is, however, still a matter of debate whether the disease progression can be influenced by modifying zinc in the diet.
Methods
We searched Medline, Embase, Biosis, ALOIS, the Cochrane central register of controlled trials, the Cochrane database of systematic reviews, and different publisher databases, and included studies that dealt with zinc in the diet and AD or cognitive decline in elderly subjects.
Results
Fifty-five studies met the inclusion criteria. Neither randomized-controlled trials nor observational studies provide conclusive evidence whether Zn in the diet is associated with cognitive decline or AD. Case-control and autopsy studies suggest decreased systemic and increased brain Zn levels, respectively.
Discussion
The current state of evidence does not allow conclusions to be drawn on whether supplementation of Zn is beneficial for the prevention or treatment of AD, although a subclinical deficiency appears common in the elderly and subjects with AD. Dietary studies with animals suggest that the impact of dietary Zn on cognitive performance depend on additional nutrients. Further studies are necessary to determine whether Zn deficiency is a risk factor for AD in general terms or under certain dietary circumstances only.
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Acknowledgements
No financial or other conflicts of interest exist for any of the authors. This study was supported by the Samueli Institute, Alexandria, VA and the Hans-Gottschalk-Stiftung, DE. The authors are grateful to Majella Horan for proofreading. ML analyzed the information, performed literature searches and drafted the manuscript. NS participated in the search and selection process. HW assisted with the analysis of critical information, contributed to the drafting of the manuscript and to the interpretation of data.