I apologize if this answer is somewhere else on VB, but I can't seem to find it.
So now I have a bottle of B12 supplements. I bought the GNC brand because it's labeled "Kosher Vegetarian". The directions say "as a dietary supplement, take one or two tablets daily". Each tablet is 500 mcg. The bottle says %Daily Value is 8333%. What does that mean? Does that mean that I can get all the daily B12 I need from only one a day? And if so, why does it say one or two?
I'm a little confused about that. For those of you who take B12 supplements, how many do YOU take daily? Is it based on a person's body weight?
National recommendations for B12 intakes vary significantly from country to country. The US recommended intake is 2.4 mcgs a day for ordinary adults rising to 2.8 mcgs for nursing mothers. The German recommendation is 3 mcgs a day. Recommended intakes are usually based on 50% absorption, as this is typical for small amounts from foods. To meet the US and German recommendations you need to obtain sufficient B12 to absorb 1.5 mcgs per day on average. This amount should be sufficient to avoid even the initial signs of inadequate B12 intake, such as slightly elevated homocysteine and MMA levels, in most people. Even slightly elevated homocysteine is associated with increased risk of many health problems including heart disease in adults, preeclampsia during pregnancy and neural tube defects in babies.
Achieving an adequate B12 intake is easy and there are several methods to suit individual preferences. Absorption of B12 varies from about 50%, if about 1 mcg or less is consumed, to about 0.5% for doses of 1000 mcgs (1 mg) or above. So the less frequently you consume B12, the higher the total amount needs to be to give the desired absorbed amount.
Frequent use of foods fortified with B12 so that about one microgram of B12 is consumed three times a day with a few hours in between will provide an adequate amount. Availability of fortified foods varies from country to country and amounts of B12 vary from brand to brand, so ensuring an adequate B12 supply from fortified foods requires some label reading and thought to work out an adequate pattern to suit individual tastes and local products.
Taking a B12 supplement containing ten mcgs or more daily provides a similar absorbed amount to consuming one mcg on three occasions through the day. This may be the most economical method as a single high potency tablet can be consumed bit by bit. 2000 mcgs of B12 consumed once a week would also provide an adequate intake. Any B12 supplement tablet should be chewed or allowed to dissolve in the mouth to enhance absorption. Tablets should be kept in an opaque container. As with any supplement it is prudent not to take more than is required for maximum benefit, so intakes above 5000 mcg per week should be avoided despite lack of evidence for toxicity from higher amounts.
All three options above should meet the needs of the vast majority of people with normal B12 metabolism. Individuals with impaired B12 absorption may find that the third method, 2000 mcg once a week, works best as it does not rely on normal intrinsic factor in the gut. There are other, very rare, metabolic defects that require completely different approaches to meeting B12 requirements. If you have any reason to suspect a serious health problem seek medical advice promptly.
I'm still a little confused. Each tablet is 500 mcg. Does that mean I should take four a week, or one or two a week?
From what I've read, a normal adult (without an absorption problem) should take at least 10 mcg if taken once/day or 2000 mcg if taken once/week. If B12 is consumed in food throughout the day the recommended amount is 2.4 mcg/day. This makes sence because if the absoption is 50% getting it throughout the day 0.5*2.4*7=8.4 mcg absorbed each week. If the absorption is 0.5% getting it once/week 0.005*2000= 10 mcg absorbed each week. So although 2000 mcg sounds like a lot roughly the same amount gets absorbed both ways.
So if you take 4/week that should be enough. If they are taken at seperate times the amount needed might be lower than that but for sure 4/week should be enough. The B12 that doesn't get absorbed goes out in your pee. The sublingual (under the tongue) are supposed to be absorbed the best; I don't know how much much of a difference there is between sublingual and regular pills. To be on the safe side I take sublingual myself.