Two factors need to be addressed in order to select the best B12 supplement: type of B12 and absorption. In my website newsletter B12, I discuss the three forms: cyanocobalamin (synthetic cyanide containing least beneficial form), hydroxycobalamin and the most beneficial form, natural methylcobalamin. The next consideration, absorption, raises several issues.
Some B12 marketers make false claims of superior absorption for their B12 products. Here is my short version to address the B12 absorption issue, followed by a more comprehensive discussion of this subject.
Pills, Capsules, Sublingual B12
Absorption of B12 supplements is minimal, approximately 1-10% for pills, capsules and sublingual products. For example, if you take 500 mcg (micrograms) of vitamin B12 orally, you are likely to absorb into the bloodstream about 10 mcg. Sublingual products work no better than swallowing a pill or capsule.
Vitamin B12 in topical preparations (creams and patches), are not absorbed through the skin, despite what marketers claim, and thus are of no value.
Absorption of B12 with a prescription nasal spray is about 10-20 times higher than that of oral/sublingual B12. Non-prescription nasal sprays are unreliable sources of supplemental B12 due to product shelf life instability and non-standardized controls over production methods and ingredients.
Prescription Strength Injectable Vitamin B12
Absorption of injectable vitamin B12 is 100%.
Unlike all other B vitamins, which absorb as readily as water, vitamin B12 is different. It is the largest of all vitamins and has a very hard time absorbing (see website newsletter B12). Vitamin B12 has a gram molecular weight of 1,355 and our skin, including under the tongue, will not let particles bigger than a gram molecular weight of 350 penetrate. Thus topical and under the tongue B12 will not absorb unless there is a strong carrier which will allow it to penetrate.
There is only one study as referenced below that shows reasonable transdermal penetration of B12, however the synthetic carriers employed are not ones that I would feel safe prescribing. Over the counter topical B12 formulas claim to use natural carriers, such as avocado oil, vitamin E, glycerin and aloe vera, however these carriers are too weak to assist in topical penetration of B12. Claims of up to 95% absorption with a topical formula are patently false. Prescription strength topical B12 products are not available for the reasons I’ve just stated.
Another problem with assessing the benefits of B12 supplementation are the faulty tests used to verify levels of absorption as discussed in my website newsletter B12 Blood Tests, Fact/Fiction. B12 blood tests provide limited guidance for making clinical and therapeutic decisions. The tests assess blood levels of B12, yet this is not a reliable indicator of cellular B12 levels which is where we get our B12 benefits. For example: “One study found lower vitamin B12 levels in the cerebrospinal fluid of patients with Alzheimer's disease than in patients with other types of dementia, though blood levels of vitamin B12 did not differ” (https://www.google.com/patents/US20080233180)
Regarding how much vitamin B12 supplementation is enough, there are many studies including the recommended daily allowance (RDA) and dietary intake recommendations that suggest 2.4 mcg of vitamin B12 daily is enough. The tests which help determine this number are the same ones mentioned above which are unreliable. Testing aside, I would suggest that 2.4 mcg of B12 daily is at best, more of a survival level of B12, and does not nearly approach levels needed for optimal health. I say this based on years of clinical experience using B12 with thousands of people.
Individuals often come to me reporting that they take between 1,000 and 5,000mcg daily of oral or sublingual vitamin B12, with little noticeable benefit. This means they were getting into the bloodstream from 20 to 100 mcg of B12 daily, way more than the RDA 2.4 mcg suggested. Despite these high and totally safe doses of B12, they still they have issues with fatigue, insomnia, anxiety, depression, weight gain, nervous problems and such, all possible indicators of B12 deficiency. Generally, after receiving one or more B12 shots from me at 2,000 mcg per shot, their symptoms vanish. If the 2.4 mcg daily requirement were accurate, then the shot would have been of no benefit.
B12 blood test assessments are unreliable. For many individuals, oral ingestion of B12 is of limited therapeutic value when there exists a B12 deficiency. Under the tongue and topical forms of vitamin B12 supplementation are just marketing ploys to sell a product. As long as one is receiving benefit from injectable vitamin B12, regardless of what B12 blood tests reveal, this is a reasonable treatment of a non-toxic vitamin.
Replacement therapy for vitamin B12 deficiency: comparison between the sublingual and oral route.