Dear List members,
This is my first query to the list and would welcome any help you may
be able to give by 24/2/99. I am writing a systematic review for the
Cochrane collaboration on vitamin C supplementation in asthma.
Can anyone direct me to references identifying or directly answer:
1> What is the time course of absorption of a single 500mg or 1g oral
dose of vitamin C in humans? (I am told 40mins but cannot find a
reference)
2 What is the time course of excretion of a single oral 500mg or 1 g
dose of vitamin? i.e. what is the washout period after a single dose?
(Verbal communications with the Nutrition Unit in Cambridge indicate
it depends on body stores, and in non-depleted Vitamin C populations
it is 6hrs (Bender) or 24-hrs or possibly 48hrs?)
3 What is the time course of excretion after longer term
supplementation with vitamin C e.g for weeks or months? (I am aware
that the body turnover of vitamin C stores is 3% per day, and plasma
levels fall to zero within 4 weeks of people being placed on vitamin-C
free diets)
I have some books on nutritional epidemiology (Margetts & Nelson) and
vitamins (Bender) and have attempted a quick medline search on
ascorbic acid but failed to get answers to these specific questions.
Some of you may have done research on this exposure in the past,
perhaps in connection with other outcomes. I will be working over
this weekend, so e-mail me if you can help. All that undergraduate
biochemistry finally became relevant!
Many thanks in advance.
Dr Bal Kaur
Clinical Lecturer in Public Health Medicine
St George's Hospital Medical School
Moving to NHS Executive - West Midlands 1/3/99.
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