It is required for the metabolism of carbohydrate gluconeogenesisamino acid leucine degradationand fat TCA cycleand for fat synthesis. No metabolic feeding studies have examined the amount of biotin required to maintain good status in active individuals. In addition, no studies have examined the impact of dieting and exercise on biotin status. There is no UL for biotin. No metabolic feeding studies have examined the amount of pantothenic acid required to maintain good status in active individuals.

In addition, no studies have examined the impact of dieting and exercise on pantothenic acid status. There is no UL for pantothenic acid. The UL for choline is 3. This range is based on a factorial approach to estimating calcium requirements and potential sweat losses during prolonged exercise, also taking into account concerns about renal stone formation. Intestinal absorption of calcium is enhanced at low levels of calcium intake approximately 300 mg due to an active transport process in the proximal small intestine, resulting in an increased fractional absorption of calcium Ireland and Fordtran, 1973.

Absorption of additional calcium from higher intakes occurs via passive cell-mediated diffusion not requiring the action of 1,25-dihydroxyvitamin D3 calcitriol. Calcium requirements in the field are based on a number of factors that affect its absorption as well as its excretion via urine and sweat. Sweat losses may be appreciable given the expected level of energy expenditure and possible environmental heat. In addition, renal stone formation has been reported in troops deployed to the Help with writing an essay East personal communication, Therefore, the major concerns considered in deriving the recommended range for calcium in the assault ration are sweat losses and the prevention of renal stone formation.

Effect of Energy Expenditure on Calcium Absorption and Excretion. Some evidence is available that indicates the fractional rates of calcium absorption are slightly higher in response to aerobic exercise in endurance trained athletes than in the untrained Zittermann et al. In spite of this increase, however, markers of bone collagen formation were decreased in that study.

Other studies have shown a slight but significant increase in 24-hour renal calcium excretion in trained young men compared to matched untrained control subjects Zittermann et al. Thus, it appears that endurance exercise at levels less than that expected in the soldier during active assault periods may result in both increased calcium absorption and increased urinary calcium excretion and decreased bone formation.

These studies did not evaluate the extent of increased losses of calcium via sweat due to the high energy level expended. Effect of Calcium Lost via Sweat. Calcium concentration of sweat in soldiers has been measured Armstrong et al. Sweat calcium concentration declines as the volume of sweat increases. Methodological problems may, in part, be responsible for differences in estimated calcium losses via sweat in the few available studies Help with writing an essay et al. Additionally, urinary calcium excretion in response to changes in sweat volume declines Armstrong et al.

Unfortunately, compensatory changes in calcium absorption have not been estimated. For soldiers who are assumed to be sweating due to heavy prolonged exercise in hot, humid climates, it is important to ensure adequate calcium intakes to replace these potential calcium losses. Effect of Sodium Intake.

High sodium chloride intake has been shown to result in increased urinary excretion of calcium in hypertensive individuals Kurtz et al. Quantitatively, 100 mmol 2,300 mg of sodium as sodium chloride increased urinary calcium excretion by 1 mmol 40 mg in postmenopausal women Nordin and Polley, help with writing an essay. Based on the results of Nordin and Polley 1987the potential increased loss i.

Effect of Dietary Protein Level. Although increased dietary protein intake increases calcium excretion Linkswiler et al. Also, more recent research suggests that the calciuretic effect of protein is partly explained by increased calcium absorption, and that calciuretic effects are considerably modified by long-term adaptation Dawson-Hughes et al. Thus, this potential effect will not be considered further in establishing a range for the assault ration. Effect of Calcium Intake on Fat Oxidation. Recent studies evaluating the effect of consumption of dairy products and weight loss have implicated calcium in enhancing whole-body fat oxidation Davies et al.

At the same time there is also evidence that losses in bone mass are attenuated on hypocaloric diets when calcium intakes are relatively high Ricci et al.

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