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Minerals
Pages 174-194

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From page 174...
... Blood calcium concentration is maintained within very narrow limits by the interplay of several hormones ( 1,25-dihydroxycholecalciferol, parathyroid hormone, calcitonin, estrogen, testosterone, and possibly others) , which control calcium absorption and excretion, as well as bone metabolism.
From page 175...
... Dietary protein enhances calcium absorption (McCance et al., 1942) in the protein intake range between inadequate and adequate levels, but has little additional effect beyond RDA levels of protein (Chu et al., 1975~.
From page 176...
... Most of the accumulation of bone mineral occurs in humans by about 20 years of age, but some bone mineral is added during the third decade. Bone mass then begins to decline slowly during the fifth decade in both sexes, as evidenced by progressive reduction of bone density.
From page 177...
... , greater bone mass was found at all ages and in both sexes in the high calcium community (Matkovic et al., 1979~. Since the rate of bone loss was the same in adults of the two communities, the finding of more bone mass in the older age groups of the highcalcium district must reflect higher peak bone mass attainment.
From page 178...
... In contrast, an increase in phosphorus intake increases fractional reabsorption and causes urinary calcium to decrease (Hegsted et al., 1981; Spencer et al., 1978~. Because of the opposing effects of protein and phosphorus on urinary calcium and calcium retention, a simultaneous increase in the intake of both, a pattern characterized by milk, eggs, and meat ingestion, has but little effect on calcium balance at recommended levels of calcium intake (Spencer et al., 1988~.
From page 179...
... The age at which peak bone mass is attained is uncertain, but probably is not less than 25 years. The subcommittee thus recommends an extra calcium allowance to permit full mineral deposition through age 24 rather than through age 18 years, as in previous editions of the RDA.
From page 180...
... Calcium retention is 200 to 250 mg/day during that period. Human milk contains approximately 320 mg calcium/liter.
From page 181...
... II. Effects of low calcium and variable protein intake on human calcium metabolism.
From page 182...
... 1970. Ef'fect of level of protein intake on urinary and fecal calcium and calcium retention of young adult males.
From page 183...
... I-2. Consumer Nutriton Division, Human Nutrition Information Service.
From page 184...
... The amount available in the food supply from unprocessed primary commodities, about 1,430 to 1,520 mg per capita per day, has been relatively constant during the past 75 years, despite marked changes in food consumption patterns (Bunch, 1987~. The mean daily phosphorus intake is approximately 1,500 mg/day for adult males (USDA, 1986)
From page 185...
... An exception is small premature infants fed human milk exclusively. Such infants need more phosphorus than is contained in human milk for the rate of bone mineralization required (don Sydow, 1946~.
From page 186...
... Excessive Intakes and Toxicity An excess of phosphorus, i.e., a calcium-to-phosphorus ratio lower than 1 to 2, has been shown in several species of animals to lower the blood calcium level anct to -- cause secondary hyperparathyroidism with resorption and loss of bone. In humans, only the effect on blood calcium level has been observed clinically.
From page 187...
... 85-3. Nutrition Monitoring Division, Human Nutrition Information Service.
From page 188...
... Extracellular magnesium concentrations are critical to the maintenance of electrical potentials of nerve and muscle membranes and for transmission of impulses across neuromuscular junctions (Aikawa, 1981~. In these processes, which also depend on calcium, the two cations may act synergistically or antagonistically (Iseri and French, 1984; Livingston and Wacker, 1976~.
From page 189...
... Purely dietary magnesium deficiency has not been reported in people consuming natural diets and has been induced experimentally only once (Shils, 1988~. In that study, seven patients were fed a formula diet after radical surgery for oral cancer (Shils, 1969~.
From page 190...
... , whereas mean intakes for adult women and children 1 to 5 years of age were 207 and 193 ma, respectively (USDA, 1987~. Recommended Allowances The only practical method for estimating human magnesium requirements is the metabolic balance procedure.
From page 191...
... An increase of 20 mg of magnesium in the daily recommendation for pregnancy should be enough to meet the needs of the fetus and maternal tissue growth, allowing for individual variation and assuming 50% of dietary magnesium to be absorbed. Human milk contains about 28 to 40 mg magnesium per liter (Lemons et al., 1982)
From page 192...
... Excessive Intakes and Toxicity There is no evidence that large oral intakes of magnesium are harmful to people with normal renal function, but impaired renal function resulting in magnesium retention is often associated with hypermagnesemia. Early symptoms of hypermagnesemia include nausea, vomiting, and hypotension.
From page 193...
... 1969. Magnesium balance and protein intake level in adult human female.
From page 194...
... 85-4. Nutrition Monitoring Division, Human Nutrition Information Service.


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