Current knowledge on zinc, copper and chromium in aging

Age-related changes in tissue and plasma zinc levels: modulation by exogenously administered melatonin

Melatonin (MEL) is synthesized mainly in the pineal gland and derived from 5-hydroxytryptophan (5-HTP). Zinc (Zn) is one of the most important trace elements in the body. Zn and MEL levels are changed with aging. The aim of this study was to investigate the age-related changes of tissue and plasma Zn levels and effect of MEL administration on these parameters. Male wistar rats received for 3 weeks subcutaneous injection of MEL (10 mg/kg). Kidney and pancreas Zn levels in old rats were significantly lower than middle-aged group. Spleen, small intestine, and plasma Zn levels were not different in middle-aged and old rats. On the other hand, MEL treatment increased Zn levels of small intestine and plasma in middle-aged rats. However, kidney, spleen, and pancreas Zn levels were unaffected by MEL treatment.

Presence of links between zinc and melatonin during the circadian cycle in old mice: effects on thymic endocrine activity and on the survival

Links between zinc and melatonin in old melatonin treated mice with a reconstitution of thymic functions have been recently documented. Concomitant increments of the nocturnal peaks of zinc and melatonin, with a synchronization of their circadian patterns, are achieved in old mice after melatonin treatment. A recovery of the nocturnal peaks of thymulin plasma levels and of the number of thymulin-secreting cells with a synchronization of their circadian patterns are also achieved. The existence of significant positive correlations between melatonin and zinc and between melatonin and thymulin or the number of thymulin-secreting cells supports the presence of links between zinc and melatonin also during the circadian cycle with a beneficial effect on thymic functions. The altered circadian pattern of corticosteron in old mice is normalized by melatonin. The existence of inverse correlations between corticosteron and melatonin, between corticosteron and zinc and between corticosteron and thymulin or the number of thymulin-secreting cells during the whole circadian cycle, suggests the involvement of glucocorticoids pathway in the melatonin thymic reconstitution, via zinc. The presence of an interplay among zinc, melatonin, glucocorticoids and thymulin may be, therefore, supported during the circadian cycle. 'In vitro' experiments from old thymic explants show a direct action of zinc, rather than melatonin, on thymulin production, further suggesting that the action of melatonin on the thymic efficiency is mediated by the zinc bioavailability. The beneficial effect of the links between zinc and melatonin on thymic functions during the circadian cycle, may be extended to a prolonged survival in aging, where, however, zinc may be more involved.

Trace elements in nutrition of the elderly. 1. Established RDAs for iron, zinc, and iodine

Trace elements play a poorly understood role in human metabolism and nutrition. In the elderly, the normal effects of aging further complicate an understanding of trace element nutriture. The RDA standards established to date for the elderly have important limitations in that "healthy" persons 51 years of age and older constitute a single, regrettably imprecise category. Although any minor elemental constituent of the body is considered to be a trace element, only 16 are currently believed to be of biologic importance to humans. A recommended dietary allowance (RDA) has been established for only three of these--iron, zinc, and iodine.

Thymic hormone deficiency in normal ageing and Down's syndrome: is there a primary failure of the thymus?

Normal individuals aged over 50 and most young Down's syndrome (DS) subjects had markedly reduced concentrations of circulating thymic hormone (facteur thymique sérique, FTS). Plasma from these two groups contained factors capable of inhibiting biological activity of FTS in vitro. Addition of zinc sulphate to plasma samples from DS subjects or the older individuals induced concentrations of FTS comparable to those observed in young healthy people and completely prevented FTS-inhibitory activity. These findings suggest that biologically active circulating thymic hormone is bound to zinc. The decline in thymic hormone activity in older individuals and DS subjects may be the result of changes in the mechanism of zinc-dependent activation of FTS molecules, which are probably associated with marginal zinc deficiency rather than with a primary failure of the thymus. Addition of zinc salt to plasma samples unmasks the presence of inactive FTS molecules.

Zinc, copper and environmental factors in the aboriginal peoples of the North West

Three-hundred Aboriginal people five to 70 yr have been studied at three missions in the north west of Australia-Beagle Bay, Lombadina and One Arm Point. The prevalence of hypozincaemia and hypercupraemia (a departure of more than 2 S.D. from the expected normal) has been assessed. Plasma iron concentration was determined. Half of the individuals had hypozincaemia and for some age groups the prevalence was greater (almost 100% for 15 to 20-year-old females at Lombadina). Hypercupraemia was prevalent and ranged from 70 to 100% for most age groups. Hypoferraemia was detected frequently. By the use of anthropometric methods the children were found to be growth retarded and to have reduced weight for height. These people are known to be infected with intestinal parasites which cause bleeding into the bowel or malabsorption which can cause losses of zinc or failure of adsorption. They prefer unleavened bread which contains phytic acid which inhibits zinc absorption. The soil is zinc deficient and the climate conducive to large losses of zinc in sweat. Geophagia is practiced and pica is found to occur in children. Preliminary evidence of elevated copper status is available. We speculate that growth failure may be related to zinc deficiency or copper toxicity.

Zinc and protein status in the elderly

Protein and zinc status were assessed in 24 community based and 66 institutionalised elderly Australians, aged 60 to 99 years. Serum albumin concentrations were significantly related to both protein intake (r = 0.36, P less than 0.001) and zinc intake (r = 0.33, P less than 0.001). Plasma zinc concentrations were not related to zinc intake (r = 0.12, P greater than 0.05) or to protein intake (r = 0.007, P greater than 0.05). Thus in aged persons with low serum albumin, it would appear useful to consider both protein and zinc intake.

Evidence for zinc deficiency in aboriginal settlements in Northwestern Australia

Four coastal Aboriginal settlements in the northwest area of Australia have been investigated for plasma trace metal status--Zinc (Zn), Copper (Cu), and Iron (Fe). The 350 Aboriginals were considered in two groups; five to 20 years of age and 20 to 70 years of age. Forty per cent to 50% had plasma Zn levels below two standard deviations from the normal and 60% to 70% had plasma Cu levels greater than two standard deviations above the normal (almost 100% at Kalumburu). Hypoferraemia was common. These results are more significant than those of a previous study of 350 individuals living at two inland settlements. The coastal missions have access to fresh meat and fish, and at Kalumburu food is prepared for the people. While the climate, soil, and the Aboriginal predilection for white flour may play a role, it is speculated that the Zn deficiency is related to parasitic infestation in the intestine, loss of blood, and failure of zinc absorption.