I yesterday watched the documentary Vitamania by Dr Derek Muller, which is about the production, benefits and risks of vitamin supplements. In the film, he briefly talked about people being blood tested in order to get some insights if they are vitamin and/or mineral deficient.

So I was wondering: When we as humans have to pretty much constantly get the vitamins our body needs to function right, can a blood test really give meaningful insights of a vitamin deficiency?

For example, if the day (or even week) before the blood test I eat less water-dissolvable vitamins like vitamin C than usual and than needed. Would that show a deficiency in the blood test thus leading to false results? Or would a deficiency only appear after a month, two, three? Or even half a year?

I already tried to search for something relatable on google. Only found some forum posts or non-scientific articles of random people claiming things like "Vitamin B gets flushed out like every day or so", which is not really specific or backed up by any literature/study. I don't really have access to any physical literature or something similar.

  • Welcome to MedicalSciences.SE :-) What books have you read or internet searching have you done to try and find an answer? Please edit your question to give details. If you have not found anything, please indicate what search terms you have used. We may be able to help with that. Sep 27, 2018 at 7:04
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    @ChrisRogers Done!
    – Suimon
    Sep 27, 2018 at 7:14
  • @Gordon I don't see why that would be relevant to the question itself. Yes, the movie talks about supplements, but my question only revolves around the blood test (or how long vitamins stay in your system, so to say).
    – Suimon
    Sep 27, 2018 at 17:32
  • @Suimon yes you are right. I removed it. I have not seen the documentary. If you live in the USA it would probably be rare to be deficient in B vitamins. However, it can happen. A patient on Lasix perhaps or some other diuretic, or a diabetic in poor control they urinate a lot and can lose the water soluable vitamins, and such minerals as potassium. However, doctors have RX options, also such patients are given information as to diet etc.
    – Gordon
    Sep 28, 2018 at 18:40
  • As far as testing goes, you would need to consult a doctor and/or lab. I am a little familiar with magnesium. Now with MG the serum level may not be a perfect test, one may want also intracellular, but I am not an expert. So a doctor should ideally order the test. Now, if it's just for curiosity's sake, then it will probably not be covered by insurance.
    – Gordon
    Sep 28, 2018 at 18:46


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