|Nutrition and Nutrients|
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Life began in the ocean. Sea salts in water remain the milieu of all living cells. The main sea-water salt, sodium chloride (NaCl), is the critical determinant of body fluids - held at 0.9% concentration in the human body, sodium intake must neither be deficient nor excessive for the body to function well. Sea water also contains trace minerals that are essential in very small quantities. These include manganese, chromium, selenium, boron and silicon.
Manganese is an essential cofactor for several important enzymes in mitochondria. One version of superoxide dismutase is manganese-dependent, and therefore the mineral is a co-antioxidant. Manganese daily requirements are not well defined, and are estimated as 2.5 - 5.0 mg/ day. Plants supply most dietary manganese. In growing animals, deficiency results in bone growth abnormalities; with skeletal disproportion, abnormal development of the knee joint and spinal curvature.
Children with abnormalities of skeletal growth should be carefully evaluated for manganese dysfunction. Adult deficiency results in weight loss, nausea and vomiting, and reduced hair growth with decreased hair pigmentation. Cholesterol levels drop with low manganese. Manganese toxicity occurs in miners exposed to very high intakes of the mineral by inhalation, and they typically develop brain dysfunction with a Parkinson's-like syndrome. Manganese supplements in the range of 2-3 mg/day may be desirable.
Selenium is required in microgram quantities and is toxic in overdose. Deficiency occurs in plants and animals raised on low selenium soils, as occurs in the western states, New Zealand, and parts of China. In Keshan County of China a regional heart disease (cardiomyopathy) was related to selenium deficiency and selenium supplementation of 1000 to 4000 microgram/day, depending on age, was successful in reducing the disease. Alcoholics tend to have selenium deficiency. Selenium has be mentioned as antioxidant since it is essential to the enzyme glutathione peroxidase which inactivates oxygen-reactive peroxides.
Selenium seems to modulate the toxicity of drugs and toxic metals. Selenium intake offers some protection against mercury poisoning. In a Finnish study increased risk of fatal cancer was associated with low selenium intakes, especially with low VM.E and VM.A intakes. Healthy populations are known to consume selenium in the range of 30-500 micrograms/day. The optimal range is likely to be 200-500 mcg/day. The supplement level may be in the range of 100- 200 mcg/day.
A single case report of selenium intoxication from supplement tablets with excessive selenium has been reported. Analysis of the tablets in one lot revealed a selenium level of 27.3 mg per tablet (182 times higher than labeled). There was marked hair loss, progressing over a two-month period to almost total alopecia; white horizontal streaking on the fingernail, tenderness and swelling of the fingertips, associated with nausea and vomiting, sour-milk breath odour, and increasing fatigue. The patient had consumed 77 of the 90 tablets, and her serum selenium level was reported as 528 ng/ml - about four times the normal level.
Silicon has been established as an essential nutrient for many animals, but not in humans. The animal evidence is so persuasive of biological function, that silicon should be considered an accessory nutrient. Silicon is the second most common element (next to oxygen) on earth; its oxide, silica or quartz is the commonest mineral in the earth's crust. Silicon, like carbon, has four binding sites, which would allow it to develop life chemistry as complex as carbon. It may be just a quirk of fate that we are an expression of carbon, rather than silicon. Given, all these credentials, we should find an essential role for silicon in life systems, including our own.
In food silicic acid, Si(OH)4, supplies the silicate ion. Deficiencies of silicate in animals produce growth disturbances, especially of bone. Silicate seems to play a role in the formation of bone matrix and the mineralization of growing cartilage growth plates. Deficiency in birds and animals produces stunted growth, with skull deformities. Aging is associated with declining tissue levels of silicon. It is not clear that increased dietary silicon would have benefits, but is clear that the role of silicate needs further evaluation, especially as an osteoporosis preventative. For growth silicon may be supplied as sodium metasilicate, in sufficient quantity to provide 25-50 mg silicate/100 gm of total food intake.
Boron is another mineral that may be considered for nutrient status. It is essential for plant growth, and preliminary evidence suggests a role for bone in preventing bone calcium loss in postmenopausal women. Boron is usually obtained from vegetables and fruit in the range of 3 mg/day.
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