Do We Have Limited Storage Capacity for Water-Soluble Vitamins?

We’ve been talking about micronutrients recently, a topic I’ve written quite a deal about—just not on this site! Since most of you have probably never seen the articles I’ve written on earlier blogs, and since they’re relevant to our current discussion, I figured it made sense to repost them here (with some light editing). This is an article I wrote for a blog that predates this one; actually, the blog that I ceased writing once I realized how much more I liked writing about climbing nutrition than just a rational approach to nutrition. I’ll have (completely) new content in two weeks, the third Monday of this month.

Our body is well-equipped to deal with the periodic absence of any given micronutrient, including water-soluble vitamins. A normal, healthy adult has a supply which lasts a minimum of two weeks for some vitamins and years for others. This store buffers against the constant fluctuation of nutrition, whether that means an inability to find food or a day of below average nutrient intake—or for that matter, a day of binge eating nutrient-dense vegetables.

Vitamins are either fat-soluble or water-soluble. Fat-soluble vitamins dissolve in fats, and as such they can be stored in our fat tissue. Water-soluble vitamins cannot be stored in the fat, but our body does store them elsewhere (usually in the liver).

Whether a vitamin is fat- or water-soluble has no influence on how much our body can store, which depends instead on the individual vitamin in question. While some fat-soluble vitamins do get stored in large enough amounts that we could go a year or longer without any and still avoid deficiency, this is also true for some water-soluble vitamins. For example, the average adult human has enough vitamin B12 in storage to last for over two years, and recent evidence suggests it may take over a year for a folate deficiency to develop in a human with normal requirements (e.g., not pregnant—if you’re pregnant or trying, do make sure to get ample folate!).

Furthermore, not all fat-soluble vitamins are well-stored by the body. In fact, the vitamin our body has the least storage capacity for is vitamin K, a fat-soluble vitamin. It takes only 13 days on a low-vitamin-K-diet to reach a subclinical deficiency, or a deficiency marked by diminished plasma levels, but not overt symptoms (blood coagulation, vitamin K’s main function, remained normal). Of course, this is still extremely rare since our gut bacteria produce some vitamin K for us, which is likely the reason we have such poor storage of it (the same is true of biotin, the second least-well stored vitamin).

Here is a graph of the average storage capacity an adult has for each vitamin (the y axis is days):

Average Adult Vitamin Storage Capacity (In Days)

Legend: Dark blue is the average minimum storage time, light blue is the average maximum storage time. Values greater than or equal to 150 indicate storage capacity of at least (but often more) than half a year.

As can be seen in the chart above, the average human has a two-week minimum supply of every vitamin, but usually a greater than 6-week supply. This includes the water-soluble vitamins, most of which we have a 2+ month supply of in normal conditions.

Some Technicalities About Water-Soluble Vitamins

Technically, some water-soluble vitamins are not “stored”, but this little fact is actually irrelevant because in all cases we store the metabolized version of the vitamin instead. Since these are the active forms, they’re actually the better chemicals to store rather than the inactive food versions.

The best example of this is riboflavin. Riboflavin is an essential vitamin because it provides the flavin our body needs to create flavin adenine dinucleotide (FAD), a critical part of our metabolism. Riboflavin itself is nothing more than a means to an end. It provides our body with a necessary molecule, seizes that molecule, forms a new compound with it, and stores that compound. There’s no reason to store riboflavin itself, and our lack of riboflavin storage does not mean we are at risk of ariboflavinosis (riboflavin deficiency).

Other vitamins have similar arrangements. Niacin does not get stored as niacin, but as the metabolite nicotinamide adenine dinucleotide (NAD) and its derivatives. Pantothenic acid is used to form CoA, also critical for our metabolism. We do not have large stores of niacin or pantothenic acid, but we do have large stores NAD and CoA. You could even make an argument for vitamin A derived from the plant-based carotenoids—we do not store carotenoids (which may have some beneficial effects on their own, but not essential effects), but we do store the retinol we create from dietary carotenoids.

If this doesn’t make sense, think of it this way: you wouldn’t stock your nuclear bunker with cash (which will be worthless after the nuclear armageddon, of course), but you can go to the store with that cash and convert it into non-perishable food items to put away for an ashy day. In this scenario, the cash is an inactive form of a vitamin that you convert to an active form for storage; it doesn’t make sense to store inactive forms of most nutrients.

You Don’t Need Water-Soluble Vitamins Every Day

It’s a myth that you need to get water-soluble vitamins on a daily basis. Since the typical adult has good stores of every vitamin, a day of inadequate intake will not affect health at all.

Many people (and even some healthcare professionals and websites) recommend you get all the water-soluble vitamins daily, and sometimes even multiple times a day to ensure optimum absorption and utilization. Usually, they recommend you do so with a supplement. This is completely unnecessary—our body is not so poorly designed that a gap of a few hours will begin the gears of nutrient deficiency. Were there any truth to this, all hunger strikes would result in scurvy, beriberi, pellagra, ariboflavinosis, and a scourge of other horrendous symptoms within a couple days. Obviously, this doesn’t happen.

At any rate, chances are you’re already consuming most of the vitamins multiple times every day because you’re eating multiple meals a day. It doesn’t matter if some meals are higher or lower in any single nutrient because it’s not necessary to balance your nutrient intake over a day (let alone over a few hours)—your body will adjust accordingly to whatever is provided. It is still important to balance your intake over the long-run, of course, so you don’t end up with a deficiency.