Vitamin C disposition in young and elderly men

Article Abstract:

Elderly people are known to be vulnerable to nutrient deficiencies. Many consume an inadequate diet, and other factors, such as the aging body's ability to handle nutrients, may contribute to these deficiencies. It appears that poor vitamin C status may be common among the elderly. The metabolism of vitamin C in 15 elderly men was compared with that in 15 young men; all subjects were healthy. Each subject was placed on a vitamin C-deficient diet (providing less than 10 milligrams per day) for five weeks. They were then given supplements of 500 mg vitamin C for three weeks. Blood levels of vitamin C changed in response to vitamin C intake in all subjects. The amount of time it took for vitamin C to reach peak levels in the test periods was long, from 3.5 to 4.5 hours, and was significantly greater for depleted subjects. The maximum level of vitamin C was significantly lower in depleted subjects. There were no differences based upon age for the time to peak or the peak level of the vitamin. The rate of absorption into the bloodstream from the digestive tract did not differ due to age or vitamin C status (depleted or supplemented). The total apparent volume of the body into which vitamin C was distributed was greater in depleted subjects, which may be due to saturation of many tissues with vitamin C in supplemented subjects. Removal of vitamin C from the blood was slower in supplemented subjects, as was the total elimination rate. Urinary levels of vitamin C were greater in people receiving supplements. Removal by the kidneys was faster, while removal by metabolic reactions was slower in supplemented subjects, meaning that urinary clearance becomes more important when high levels of vitamin C are present. No differences due to age were found in results concerned with removal of vitamin C from the body. The results show that in healthy subjects, there are few differences between young and elderly men in their ability to handle vitamin C. (Consumer Summary produced by Reliance Medical Information, Inc.)

Health aspects, Aging, Aged, Elderly, Demographic aspects, Food and nutrition, Vitamin C, Vitamin C metabolism, Vitamin metabolism

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Vitamin A in parenteral nutrition: uptake and distribution of retinyl esters after intravenous application

Article Abstract:

Vitamin A is needed for growth, reproduction, vision and healthy skin. After this nutrient is consumed in food, it follows a particular metabolic pathway from the intestines to the liver to the blood, which carries vitamin A to tissues in need of it. But if vitamin A is supplied by total parenteral nutrition (TPN, intravenous feeding), the way it is transported and distributed to target tissues is different; TPN delivers nutrients to the body directly through a vein, bypassing the digestive tract completely. Scientists do not understand how vitamin A is used by the body when given in TPN, and this knowledge would be helpful in choosing the dosage to give TPN patients. If too little vitamin A is provided, patients can become deficient, but an excess can be just as harmful because vitamin A is stored by the body and can reach toxic levels. Blood tests do not reveal the amount of this vitamin stored unless the individual has almost no stores left or is reaching toxic levels. Rats were used to study the uptake, distribution and storage of vitamin A supplied parenterally. Animals that were vitamin A-depleted and vitamin A-sufficient were infused with the retinyl esters and then killed; this form of the vitamin was absorbed by all the body tissues examined. It was concluded that retinyl esters given parenterally over the short term may successfully prevent vitamin A deficiency in patients on long-term TPN. Individuals with liver disease may benefit the most from this approach; their livers do not metabolize vitamin A normally and this route bypasses the liver.

Research, Physiological aspects, Parenteral feeding, Parenteral nutrition, Vitamin A, Vitamin A deficiency

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