Zinc and platelet membrane microviscosity in Alzheimer's disease. The in vivo effect of zinc on platelet membranes and cognition.

Objectives: To investigate the effects of oral zinc supplementation on: (i) plasma zinc concentrations; (ii) platelet membrane microviscosity in vivo; and (iii) cognitive function of Alzheimer's disease (AD) patients.

Design: An open-labelled pilot study.

Setting: University of Stellenbosch Medical School and Stikland Hospital.

Subjects: Six volunteer AD patients.

Outcome Measures: Plasma zinc levels, platelet membrane microviscosity and cognition (MMSE and ADAS-cog tests).

Results: Oral zinc supplementation (30 mg/day) did not increase plasma zinc levels significantly, but significantly increased platelet membrane microviscosity (P = 0.02; 6 patients). Four patients, who underwent 12 months of evaluation, showed modest cognitive improvement on psychometric testing (Mini-Mental State Examination and the cognitive portion of the Alzheimer's Disease Assessment scale scores).

Conclusions: While earlier literature promoted the use of zinc in AD patients, a recent study has contradicted this and implicated zinc in the aetiology of Alzheimer's disease. On the basis of the above results, it may be premature to single out zinc as a causal agent in AD.