What I look for are things that improve my life and then I pass it along. So I have been doing a lot reading of late on this vitamin. Before I lose your interest I am going to list a bunch of symptoms, then get into why I think it is LIKELY you may be deficient.
Depression, nervousness, memory loss, Alzheimer like symptoms ( looks like Alzheimer but  is not ), numbness of the feet, back pain, red and sore tongue, and  heart palpitations. Interesting isn't it. Realize as you read these symptoms there are "degrees" of affliction. Now before you go away, I will list the medications in which you are LIKELY to be deficient.
You take the following medications, birth control pills, a cholesterol lowering drug (statins), metaformin for type 2 diabetes, protein pump medications to control acid reflux, antacids, potassium supplements, dilantin for seizures and nicotine if you smoke.
And now the conditions that may cause a decrease in absorption of B 12. Alcoholism or a drink or two every day, old age, and vegetarianism.  Older or elderly people have less acid in their stomach's as the get older! Anything that reduces acid in the stomach interferes and decreases absorption!
There is some controversy about how B 12 should be taken. Some say it should be taken orally or sub lingual ( under the tongue). Some say you should get it as a shot at your doctor, but I am confident that taking it sub lingual will work. Heck if it does not get absorbed sub lingual, you will swallow it eventually anyway! A win win situation. The argument is that not much is absorbed by this route and that is true a great deal of the time. This is why my readings suggest that LARGE doses should be taken to compensate for this lack of efficiency. As little as one percent of the B 12 taken sub lingual/ oral maybe absorbed!
To my knowledge there never has been a over dosage of vitamin B 12 that caused any symptoms. I have even seen articles that tell of people with a yeast infection of the gut and resultant HUGE doses of B 12 and no side effects. These levels are levels that will not occur with any practical usage of the B 12 dosages I am going to suggest. So I do not see a down side to taking B 12 and a lot of upside. ( If there is B 12 in your Multivitamin there is not much and that goes for B complex vitamins also). Who wants to be diagnosed with Alzheimer's disease, and after your demise, for your family to find out it was just a B 12 deficiency. Not me!
So here is what I see recommended. A couple milligrams a day for a month then maybe a milligram everyday thereafter. Now you can go and get a blood level done by your doctor and he may tell you it is normal. My readings suggest that B 12 levels in the elderly should be HIGH normal or you can have signs you are deficient.. I have pointed you in the right direction and now it is up to you to follow up with your own readings. It is your health after all. It is all out there on the internet and you should not take for granted that you Health Provider is informed on this subject. Their sphere of expertise tends to be treatment and not prevention and is very frequently deficient in subjects related to what I blog about.
May the new year be better and better for you in every way......
BB

I am not going to say the typical thing like, lose weight, exercise etc. Those things require real effort and are a really good idea, but these suggestions are different.
Number one. Stop taking multivitamins or at least don't take them every day. Go to your multivit bottle and look at it right now. If it contains over 2500 iu of vitamin A .....stop it now. Vitamin A interferes with the utilization of vitamin D. In a study of 38,000 people death rate was 2% higher in the multivitamin takers. Vitamin A can be toxic in high doses and thought, wrongly, to decrease infection rates. Now, if some one was to come out with a multivitamin that had the amounts of vitamin A and D switched they would indeed have a healthy product.
Two. If you take a prescribed vitamin D look at the label. If it says ergocalciferol or vitamin D2. Stop it completely. It is not a naturally occurring vitamin in the human body and actually increases death rate when compared to D3. The other name for D3 is cholecalciferol.
Got any time left over....try the first sentence. It will help!
Merry Christmas
Bruce Bennett

. Let me suggest that it would be a good thing if your soldier friend or relative was stronger, had less pain, took a lot less motrin and was smarter on the battlefield. Smarter stronger on the battlefield is not a bad thing. So I will tell you about a couple of studies I have seen that strongly suggest this is true.
The first study is about a bunch of rats. One group is dosed up with vitamin D and the other group were not. The rats were put in a drowning pool. There was only one place in the whole pool that a footing could be found that would save their lives. The rats with a high level of vitamin D found that footing very quickly and the others without vitamin D did not. I don't think they let the other rats drown, but they sure thought they were going to.
So lets say a person is in dire straights on the battlefield of Asia. If he could come up with a solution that would save his life, would that not be a good thing. No doubt about it.
Next you take two groups of people. One you dose up optimally and the other you do not. Put them on the treadmill for three months. In three months the group with the optimum dose of vitamin D was stronger and could go longer on the treadmill than the other group. This was done with a group of elderly people in a nursing home. Stronger means less falls etc. Not a bad thing and I have seen the same kind of studies done in athletes. Did you know the Russians were dosing their atheletes, for the Olympics, with vitamin D. They did other things also, not legal, but that is another story.
Two seasons ago the Black Hawks Hockey team won the Stanley cup. They changed just one thing. They started taking vitamin D and saw less serious injury, less pain treatment, and sickness. This after being non competitive the previous season.
The facts are that vitamin D goes to 2,000 to 3000  genes that are good for health and in the process turning off bad things like cancer and reducing the likely hood of viral and bacterial infections. Do I know anybody that would not benefit from addressing the proper dosing of vitamin D. The answer is no, but there maybe a life guard, some where, that works year around and is exposed to the sun at least 20 minutes a day and is under the age of fifty. This guy or gal would have a optimum level. Above the age of fifty the ability to make use of the sun in a adequate way is diminished, and if you are black your time in the sun will need to be up to five times longer to get that optimum dose. Black skin protects you from sun damage of the skin. Not a concern in people who where clothes and live in a temperate climate. Proper dosing is 1k per 25 lbs. Test in three months. Read my "about" on this blog. It addresses other concerns with need to be addressed also.
What is the real subject here? Simple, we all suffer from the effects of living in civilization which has deprived us of essential nutrients. We suffer severally for this!

copy and paste
http://www.sciencenews.org/view/feature/id/5492#comment_337186

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The difference between a prophet and a madman
December 7, 2011 -- Dr. John Cannell

I realize that when I write for a journal that most of my readers cannot access my writing. This month the British Journal of Nutrition invited me to write an article; it is here, below. To put the article into context, my long-time readers will remember the excitement back in 2005 when I discovered that vitamin D appeared to prevent influenza.

Cannell JJ. The difference between a prophet and a madman. Br J Nutr. 2011 Nov;106(9):1317-8.

Edgar Hope-Simpson was a self-taught young genius epidemiologist who turned into a gracious old man obsessed with his hypothesized ‘seasonal stimulus’ for epidemic influenza. He was the scientist who discovered the aetiology of shingles, but he was also the man who seemingly wasted the last 20 years of his life trying to untangle the manifold mysteries of influenza. Among his last written words, he cordially pleaded with the giants of influenzology, ‘it might be rewarding if persons, who are in a position to do so, would look more closely at the operative mechanisms that are causing such seasonal behaviour’. He died bereft of any recognition of his discovery that epidemiology of influenza is controlled by an unknown ‘seasonal stimulus’, whose character is dominated by a distinct aversion to sunlight.

Edgar Hope-Simpson had the rare gift of understanding the difference between fact and theory. For example, he knew that the statement, ‘children with rickets have frequent pneumonia because their rib cages are too weak to cough effectively’, contains one fact and one theory. Similarly, ‘influenza is more common in the winter due to overcrowding’, and ‘influenza is spread from person to person via respiratory droplets’, and ‘influenza spreads so rapidly because it is highly contagious’. He knew all these statements contain one fact and one theory and by distinguishing fact from theory, he wrote what is still the best book on influenza.

Indeed, his book led directly to two influenza publications from our group, the last one of which we used vitamin D to explain nine major conundrums of influenza. We predicted that vitamin D will both prevent and treat influenza, once modern medicine learns proper maintenance dosage(25mcg (1,000 IU/10 kg per day), not unlike the dosing of thyroxin.

The mechanism of action of vitamin D in preventing and treating various infections, a mechanism that led Science News to characterize vitamin D as the ‘the antibiotic vitamin’ has become evident only very recently. Both epithelial cells and macrophages increase expression of the antimicrobial cathelicidin upon exposure to microbes, an expression that is dependent upon the presence of vitamin D. Pathogenic microbes, much like the commensals that inhabit the upper airway, stimulate the production of a hydroxylase that converts 25(OH)D to 1,25(OH)2D, a seco-steroid hormone. This, in turn, activates a suite of genes involved in defense.

In the epidermis, vitamin D induces additional PAMP (pathogen associated molecular pattern) receptors, enabling keratinocytes to recognize and respond to microbes. Thus, vitamin D appears to both enhance the local capacity of the epithelium to produce endogenous antibiotics and – at the same time – dampen certain arms of the adaptive immune response, especially those responsible for the signs and symptoms of acute inflammation.

All this leads to the recent paper by Berry et al. in this edition of the British Journal of Nutrition, the first paper to take season, lifestyle and health factors into account while associating 25(OH)D levels and self-reports of respiratory infections. The effect size was large, about a 10% less risk of infection for every 4 ng/ml increase in 25(OH)D. Summer-time levels never reached 40 ng/ml the level that some feel is the lower limit of health.

The authors remain hesitant, for the reasons they list, to recommend vitamin D for asthmatic children. In the authors’ discussion of Ginde et al. they failed to note that the association between low vitamin D and infection was about four times stronger in asthmatic children than in non-asthmatic ones. Furthermore, while asthmatic numbers described by Urashima et al were small, they were highly significant, finding that 1,200 IU/day of vitamin D effectively prevented exacerbations in asthmatic children (P<0·006) compared with placebo.

As a practitioner, I believe the medical community should consider vitamin D deficiency as a ‘known health hazard’, and aggressively treat it – in asthmatic individuals as well. Although anecdotal, I have observed high doses of vitamin D (5,000 IU/10 kg per day for 6 months then reduce to maintenance) seemingly ‘cure’ some childhood asthma in about 6 months. I hesitate to mention this but cannot find ethical reasons that allow me to exclude it from my comments.

Finally, to be sure, the study by Berry et al. speaks only of the respiratory system, yet antimicrobial effects of vitamin D may be more generalized. Recently, researchers in Tennessee wanted to know if vitamin D levels were associated with overall mortality in the intensive care unit (ICU). They found patients were almost twice as likely to die during an ICU stay if they had vitamin D deficiency (<20 ng/ml).

Respiratory infections are but one failure of the immune system that lead children into the ICU. Meningitis is another, a grim wintertime scythe that should be treated not only with conventional antimicrobials, but also (in my opinion) with pharmacological doses of vitamin D (10,000 IU/10 kg per day for several days). And, should any promising observer note an association between meningitis and a ‘seasonal stimulus’, and then suffer the scorn of their colleagues, remember Dr. Edgar Hope-Simpson and remember also that time alone distinguishes a prophet from a madman.

Did I get your attention?!  I am going to talk about this a little bit then let you see the article which will require a copy and paste. First we do not eat correctly or drink correctly in this modern world we call civilization. Our ancestors, before 15,000 years ago were all hunter gathers and drank from streams and lakes. Very seldom did they have grains of any kind because they were not cultivated until 15,000 years ago. Meat was lean and wild. No antibiotics and they definitely were not fattened in a feed pen some place then harvested. So roots and meat. No twinkies or frozen meals. The water was not processed and came from streams and lakes that were full of minerals.

So we eat all this processed food and drink processed (low in magnesium) water. This means we are not getting enough magnesium in our diet. Just about everyone is low. If you drink well water and check it for purity from time to time you are better off than everyone else because it is a natural high source of magnesium.
Interestingly studies have been done that show people who have low levels of magnesium have sudden heart attacks even in those without a prior history of heart troubles. That is fact one.

Fact two, to repeat myself, everyone on a normal modern diet is low in magnesium.
Fact three, if you take vitamin D you will lower your magnesium level because vitamin D uses magnesium to make the hormone calcidrol. Remember, vitamin D is not really a vitamin. It is a prohormone.
Fact four, if you lower your magnesium level even more it is logical to assume it will increase the likely hood of a heart problem. Magnesium calms the heart and helps keep it regular. It does a lot of other good things too, but I will not go into that now!

SO IF YOU TAKE VITAMIN D TAKE MAGNESIUM IN SOME FORM OTHER THAN MAGNESIUM OXIDE!  I recommend magnesium malate because it helps with muscle pains ( sore back and neck muscles) and magnesium oxide is a poor material to take because it will not be absorbed well. However, magnesium oxide is a good laxative...it stays in the gut thus causing the problem and not helping the heart as much.

THERE IS A SITUATION THAT MAGNESIUM SHOULD NOT BE TAKEN WITHOUT MEDICAL SUPERVISION. If you have poor kidney function the magnesium level could climb. This would induce muscle flaccidity and weakness. The treatment is to stop the magnesium. One more caveat. The blood test for magnesium is not a good one. Less than one percent of the magnesium in the body is in the blood so it is a poor reflection on the true state. A test showing you are low  indicates a low magnesium level, but a " normal" results can not rule out that you are still low. Many medical professionals are not familiar with the above fact.

So do your best to be healthy and realize that civilization comes with a price. It makes you unhealthy and the medical profession is very happy to treat the results of that. For me, preventing the these illnesses of civilization  in the first place is my objective.

So now the article. Note that he does not even mention magnesium in the article. The medical professionals are amazingly ignorant on what it takes to be healthy and prevent disease. They love to treat it though!

Got questions. Don't understand. I am at k2pdj2000@yahoo.com  
http://www.agemed.org/AMMGejournal/November2011/AskDrDeSilvaNov2011.aspx