Nutritional Needs in Cold and High-Altitude Environments Applications for Military Personnel in Field Operations (1996) / Chapter Skim
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14 Micronutrient Deficiency States and Thermoregulation in the Cold
14 Micronutrient Deficiency States and Thermoregulation in the Cold
Pages 245-256
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From page 245... ...
Among these disorders is the inability of mammals to maintain body temperature adequately in the cold. The purpose of this review is to present current concepts in temperature regulation, with particular emphasis on temperature maintenance in cold environments, and to relate physiologic changes caused by micronutrient deficiency to impaired thermoregulation.
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From page 246... ...
Metabolic heat in mammals comes from the following metabolic sources: basal metabolism, postprandial thermogenesis, diet-induced thennogenesis, shivering thermogenesis, and nonshivering thermogenesis (Gordon, 19939. Shivering and nonshivering thermogenesis are the main sources of heat production utilized during cold exposure, and both may he affected bv micronutrient deficiency states.
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From page 247... ...
, but most adult mammals, including adult humans, have only a small amount of detectable brown adipose tissue (Lean and James, 1986~. The increase in thyroid hormone production and metabolism associated with cold exposure is the probable initiator of heat production in brown adipose tissue (Guyton, 1986~.
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From page 248... ...
Iron-deficiency anemia results in decreased oxygen transport from the lungs to "issues, and this reduction in oxygen availability inhibits physiological responses to cold, including peripheral vasoconstriction, a heat-conserving process, and increased metabolic rate, a heat-generating process. Hypoxia, created by reducing the oxygen content or the pressure of inspired air, results in hypothermia in rodents (Gautier et al., 19913.
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From page 249... ...
After an increase in the hematocrit levels of iron-deficient rats, plasma norepinephrine concentrations remained elevated (Dillmann et al., 1979) , and the norepinephrine content of heart and brown adipose tissue remained depressed (Beard et al., l990b)
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From page 250... ...
Coupled with in vitro assessments of tyrosine hydroxylase activity, these results indicate that increased sympathetic firing rate, rather than impaired synthesis, accounts for the decreased norepinephrine content found in the tissues of iron-def~cient rats and perhaps the increased concentrations of norepinephrine in the plasma and urine of iron-deficient humans. Thyroid Hormones In humans, iron-deficiency anemia is associated with changes in plasma thyroid hormone and norepinephrine concentrations that mirror those seen in iron-deficient rats.
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From page 251... ...
In summary, iron deficiency profoundly alters thyroid hormone in animal models and to a lesser extent in humans. The most recent kinetic studies suggest the primary effect is a central nervous system-modulated one; that is, iron deficiency changes the hypothalamic control of thyroid metabolism.
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From page 252... ...
Animal studies showed that a copper-deficient animal has a lowered body temperature along with lowered circulating thyroid hormone levels. This is reminiscent of the observation of poor thyroid function and thermoregulation seen in iron-deficient rats (Hall et al., 1990~.
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From page 253... ...
Finch, and W.L. Green 1982 Interactions of iron deficiency, anemia, and thyroid hormone levels in the response of rats to cold exposure.
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From page 254... ...
1981 Nonshivering thermogenesis, brown adipose tissue, and obesity.
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From page 255... ...
Hall, and M.J. Marchello 1992 Impaired thyroid hormone status and thermoregulation during cold exposure of zincdeficient rats.
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From page 256... ...
1986 Effects of thyroid hormones on oxygen consumption, heat production, and energy economy.
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