helvella - Water Solubility and Safety

Wherever you look in discussions on medicines and supplements, you see the claim that because a particular substance is water soluble, it is inherently safe and simply cannot be a problem. After all, you will just get rid of it when you urinate.

This is a spectacular mis-understanding of reality.

So far as I can tell, the origin of its widespread repetition lies in the discussion of fat soluble vitamins - such as vitamin A and vitamin D. If taken in excess, these can build up and get stored in body fat, Once stored, they can be retained for extremely long periods.

Thus the advice to be careful to avoid taking an excess of any such fat soluble vitamins.

However, this seems to have become inverted. Rather than a warning about being especially careful with substances that are fat soluble, it is sometimes - often - used as a universal justification for taking any amount of substances which are water soluble. Simply because there is a potential for urine to carry them away. Though being water soluble is usually necessary, it is not, on its own, sufficient.

1. Being able to get rid of a substance does not preclude it causing damage on the way through the body.
2. There are many extremely water soluble substances which are potentially seriously harmful.
   
3. Getting rid of some water soluble substances can damage the kidneys.
   

Examples of substances which are water soluble but potentially damaging include:

• Extremes like potassium cyanide which are outright deadly poisons. In any other than the most infinitesimal amounts, it will kill before even reaching the kidneys;
  
• Sea-water or brine (or other liquids with lots of sodium, potassium or other minerals dissolved in them) which we all know are problematical despite common salt being essential;
  
• And alcohol (ethanol), about which I probably need say nothing.

Kidney Damage

Substances which can damage the kidneys, that is, are nephrotoxic, and water soluble include iodine and some contrast media, vitamin B6, vitamin B9 and vitamin C. 

Nephrotoxicity is even more of an issue in those with any existing kidney issues. Indeed, the impairment of function can reduce the maximum safe intakes of many supplements and medicines.

Also, in those who have already have impaired kidney function, all claims of water solubility meaning that substances are simply excreted in urine need to be reconsidered. Impaired kidney function is quite common. Indeed, kidney function is one of the many things that is observed to deteriorate with age, illness and some medications.

This article lists a considerable number of nephrotoxic medicines:

Nephrotoxic Medications

Osmotic Pressure

There are also some substances such as magnesium oxide/hydroxide which might seem to be soluble but actually pull water out of our tissue.

Solubility also varies and can be very sensitive to acidity (pH). Thus, a substance could be soluble in the acidic environment of the stomach, but not in the neutral/alkaline environment present in most of the rest of the body. Or vice versa.

Advertising and Promotion

Obviously, being able to claim a substance is safe because, should you happen to take more than you need, you simply get rid of it in your urine, helps with sales.

It diminishes any fears people might have about the product. It reassures that, even if you did have a minor side effect or adverse reaction, you will be urinating it out so it is only transient and should not be a concern.

At the same time, it limits any concern people might have about large doses in general. Whereas 100% of daily requirement could perhaps initially appear to be a reasonable universal maximum, these water solubility claims tend to suppress concerns people might have about larger amounts.

Checking a single well-known multivitamin, ten substances are present in amounts over 100%:

Vitamin E (α-TE)    24 mg 200%
Thiamine                 1.65 mg 150%
Riboflavin                2.1 mg 150%
Vitamin B6              2.1 mg 150%
Vitamin B12            7.5 μg 300%
Vitamin D                15 μg 300%
Biotin                       75 μg 150%
Folic acid                300 μg 150%
Niacin (NE)             24 mg 150%
Pantothenic acid     9 mg 150%

(Not all the above are even claimed to be water soluble. The full list has been included for context.)

These larger amounts also appear to deflect from consideration of dietary issues. It becomes very easy to assume that people can get most of their vitamins from a tablet. 

Special Cases

Vitamin B12 undergoes a complex process in order to be absorbed. Very large doses of oral B12 are used to overcome deficiencies in this absorption process. And there is effectively no evidence that there is any issue with extremely high doses of B12 - even when injected.

 

If you wish to link to this page on HealthUnlocked, copy the entire dark red text below and paste into a post or reply.

[i][b]helvella - Water Solubility and Safety[/b]

A blog post discussing what effect water solubility really has on the safety of supplements, medicines and other substances that are ingested.

Last updated 10/02/2025[/i]

Link to blog:

https://helvella.blogspot.com/p/helvella-water-solubility-and-safety.html

If you find anything incorrect, misleading, typos, links that don’t work, etc., please let me know. Go to my profile and use the contact details there.