Chemical and physiologic changes with aging can lead to increased susceptibility to disease. Diets of the elderly are often deficient in nutrients because of cost, loss of teeth and malabsorption. Of the 40 micronutrients that are essential in the diet, zinc can be of great benefit since it increases immunity.
Zinc is important in immune health, antioxidant activity, proliferation, differentiation, and apoptosis. The body’s stores of zinc are limited. Humans don’t tolerate prolonged low intakes of zinc without developing immunity problems.
Metallothioneins (MT) are metal binding proteins which control zinc balance. MT contain twenty cysteine molecules which bind 7 zinc atoms. This form of zinc protects it from radiation, mercury, cadmium, lipid peroxidation, reactive oxygen species, etc. MT assure a zinc supply during low intake and prevent excess zinc when it is abundant. Nitric oxide causes zinc release by MT.
MT increase with aging. The binding of zinc to increased MT may be the reason zinc is less available for immunity with aging. Centenarians have low MT production. This may be why their unbound zinc is more available for immune functions for improved longevity. Zinc supplementation in mice through life seems to prevent age-related immune problems due to a reduction of cancers and infectious disease.
The results of zinc supplementation research in the elderly are variable because of the various doses used. The RDA is 10-25 mg/day. The tests seem to indicate that the best results are found when treatment is given for limited periods of time. Prolonged treatment may be detrimental and treatment cycles are suggested. Treatment of 15 mg/day for 1 month has been shown to benefit the elderly, those with Down’s syndrome, and the infected elderly.
CONCLUSION: Zinc supplementation is important to immunity and the ability of people to reach old age. There are many variables which require further research.
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