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Preciser phrasing of the question: Do I need to consume the daily recommended dose of water-soluble vitamins every single day? Or is it sufficient if my consumption averages to the daily dose over a longer timeframe (and what timeframe would that be)?

I am aware that:

  • fat-soluble vitamins can be stored for a long time (months, possibly even years in some cases).
  • water-soluble vitamins can (with the exception of B12) only be stored for a short time.

However, I have not found any clear answer to how short the "short time" for water-soluble vitamins is (a single day? A week? Not at all?). Answers I found are usually vague or inconsistent with each other (and also not sourced):

"it is recommended that you replenish your stores of water-soluble vitamins every few days" [1]

"you should try to get them regularly from your diet." [2]

"water-soluble vitamins dissolve in water and are not stored by the body. Since they are eliminated in urine, we require a continuous daily supply in our diet." [3]

Background: I am currently trying to eat healthier than I used to. One thing I want to track is my vitamin intake to ensure that I do not develop deficiencies.

However, I am not sure how granularly I have to keep up with daily recommended doses.

Example: The German Nutrition Society recommends 110mg of Vitamin C daily for me [4]. Does this mean that I actualy need 110mg every single day in order to not develop a deficiency long-term? Or is it sufficient if I track my intake, e.g., on a weekly basis (requiring 770mg per week)?

I am aware that there are also differing opinions about the actual amount per day that is needed (e.g., 110mg in Germany, 90mg in the US [5]) but this is out-of-scope of my question.

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1 Answers1

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You do not need to get 100% of Recommended Dietary Allowance (RDA) of every water-soluble vitamin every single day. It depends on the vitamin, but you can safely assume it is enough you get about 7 RDAs of each in a week.

It is often said that water-soluble vitamins (B complex and C) are not stored in the body, but this is not exactly true. There is always a "pool" of vitamins in the liver or somewhere else from which they are available for few weeks at least.

There is no known vitamin deficiency that would develop in a healthy well-nourished adult within a week of abstinence from that vitamin.

Time in which symptoms can develop after stopping or greatly reducing vitamin intake:

  • Vitamin B1 (thiamin): within 12 weeks (WHO)
  • Vitamin B2 (riboflavin): several months (Britannica)
  • Vitamin B3 (niacin): in 4 months (WHO)
  • Vitamin B9 (folate): within a month ; vitamin B12 (cobalamin): in 3-5 years (Emedicine)
  • Vitamin C: within 1-2 months (NIH-ODS, WHO)

It requires weeks to months of undernutrition for deficiencies of water-soluble vitamins (except vitamin B12) to develop, whereas deficiencies of fat-soluble vitamins, and of vitamin B12, require more than a year to develop due to larger body stores (US Pharmacist).

Jan
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  • Difference between regulatory bodies/countries indicate that the numbers are largely arbitrary. Unless a real deficiency develops much lower doses are quite fine. Take VitC. USA: 90mg (was lower before) Germany 110mg (was lower before). Mean daily intake in Netherlands only 78mg, yet zero cases of scurvy… – LаngLаngС Jun 21 '19 at 16:13
  • I'm thinking all the time that RDAs are probably much greater than "minimal" and even "optimal" amounts. They pumped the RDA for potassium to 4.7 g/day, which is just unrealistic for many people. – Jan Jun 21 '19 at 16:16