The body’s Vitamin B12 Store: a Necessity or a Luxury?
Our bodies store greater amounts of vitamin B12 than they do for any other vitamins; an estimated 2000 – 4000 µg, the majority of which is found in the liver.1-4 Theoretically speaking, the body could function on a minimum provision of 1 µg per day for up to 10 years. This is one reason why the serious effects of a vitamin B12 deficiency can take several years to become apparent.
A consensus is yet to be reached regarding optimal storage size and biological relevance regarding the body’s reserves. Some argue that the body stores vitamin B12 to ensure that irregular intake doesn’t have too great an impact on health, indicating how important it is for us. It could also be due to the fact that meat was less common in the diet of our ancestors.
Other researchers consider it to be a luxury phenomenon,5 as it is our view that high level and excess meat consumption in industrialized countries has led to the liver being rich in vitamin B12. The fact that the body breaks down and excretes excessively high quantities of B12 supports this view.
There are likely elements of truth in each belief. While the body does appear to store B12 naturally, this might be as a result of the food market in industrialized countries which delivers far beyond natural needs. It is widely believed that B12 levels under 500 µg are critically low.6
The Structure of the Body’s B12 Storage System
The following values are the average levels found in the body’s reserves:7
If vitamin B12 stored in the liver is required, the adenosyl group breaks away to transport cobalamin to the cells where methylcobalamin and hydroxocobalamin are formed. Methylcobalamin levels are always lower, not because there is a higher demands, but because once formed it is used immediately. Hydroxocobalamin spends longer in the body.
Depletion of the Body’s Vitamin B12 Reserves
The first indication of a deficiency resulting from poor diet will start to become apparent on average after 2 – 8 years.8,9 Vegetarian children and infants with mothers who are B12 deficient are unable to develop a bodily reserve and so a deficiency can occur very early on in life.
Every day around 0.1% of our bodily store is lost with urine, regardless of how much is being stored. This means that the higher the level of reserves, the higher the amount of B12 that will be lost.11
It is currently assumed that store levels between 1000 – 2000 µg should ideally be maintained to ensure coverage during times of increased need, such as intestinal diseases.
The Consequences of Low Vitamin B12 Stores
Levels above 500 – 1000 µg in the liver are considered to have no recognizable health benefits. However, a measurement within this range means that the capacity is not saturated and so bodily functions will not be affected.
The implications of low vitamin B12 stores are quite serious. In the case of persistently low levels, serious deficiency symptoms can manifest quite quickly.
To avoid such an occurrence, it is recommended that the store is taken into account during daily B12 intake. This has already been determined by RDA and, depending on the country, this figure lies typically in the range of 2.4 – 3 µg to cover the body’s daily need and to top up the body’s store. In the USA, the RDA is currently considered to be 2.4 µg for adults.
However, most vitamin experts are doubtful that this quantity is actually sufficient. (See article dedicated to vitamin B12 requirement).
Replenishing the Vitamin B12 Reserves
The recommended daily dose assumes that there are already sufficient vitamin B12 levels in the body store. A vitamin B12 deficiency is usually only noticed once reserves have been fully used up for some time. This daily dosage is not sufficient to replenish the body’s depleted reserves.
Most often, when a deficiency is present an initial high dose will be administered to refill body stores. The use of oral supplements such as tablets, capsules and drops for this will have a limited effect. Even a really high dose oral supplement of 1000 µg would only deliver at most 13 µg, due to the body’s absorption mechanisms for B12.
To obtain 2000 µg in this way would take over six months. Because of this, a vitamin B12 injection is often used in this scenario, where absorption is equal to the amount of active ingredient administered; typically up to 700µg. The body stores will be refilled to optimal levels after a few injections.
For a regular supply of vitamin B12, oral supplements are more appropriate, as speed is not a priority. The daily requirement can be covered and the body stores topped up sufficiently with the correct dosage. The supplementation must be taken regularly and maintained for a prolonged period of time, otherwise deficiency could return quickly.
Vitamin B12 Treatments & the Body’s Storage
Today, the maintenance of a healthy vitamin B12 body store is viewed as very important and should be considered in conjunction with vitamin B12 therapies. When taking oral supplements or after a severe and longstanding vitamin B12 deficiency, a generous dose of 500 µg is advised for several months before it can be eventually reduced. A mixture of methylcobalamin and hydroxocobalamin would be optimal, because the later is stored most effectively.
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