What’s Vitamin B12 got to do with it?

Deepti Pradhan
4 min readSep 12, 2016


Have you felt inexplicably tired, achy, or perhaps confused recently? There could be a host of reasons that cause this; some easier to address than others. The human body and human physiology is exquisitely tuned to manage many biochemical assaults, including reduced availability of some nutrients. This is because of inherent redundancies in our systems, whereby a biochemical destination can be reached via multiple routes. Consider how we convert the raw materials in our bodies, for energy. Carbohydrates, proteins, and fats can all be broken down for energy, and based on the circumstances, the body accesses one of those over the others. Which is why if you are in good health and skip a couple of meals, you are not incapacitated. You still have the energy to function.

So what happens when these reserves are called upon for energy? ATP or adenosine triphosphate is a readily accessible molecule in cells, which can be converted to that required energy: mechanical energy for running; or heat energy if you’re cold and so on. ATP is therefore often viewed as the primary currency for energy in biological systems. But where does this ATP come from? It is the result of the breakdown of those carbohydrate, protein, or fat reserves.

Breaking down simple carbohydrates is the fastest way to get to the ATP. Glucose, perhaps the most abundant simple carbohydrate, is made up of six atoms of carbon, twelve of hydrogen and six of oxygen. When one molecule of glucose is broken down in absence of oxygen, it uses up two molecules of ATP and results in two additional molecules of ATP. The glucose is now in most instances transformed into two molecules of pyruvate each of which is made up of three atoms of carbon, four atoms of hydrogen and three atoms of oxygen. Clearly this is not terribly efficient, and the process can continue to yield more molecules of ATP when pyruvate is oxidized and enters the Krebs cycle or tricarboxylic acid (TCA)cycle in the form of acetyl-CoA. This cycle is considered by some to be a body’s energy universe hub. Because to get the maximal energy from a molecule of protein or fat, like glucose, they too need to go through the Krebs cycle — either as acetyl-CoA or at some other point in the roughly nine steps of the cycle. And don’t forget, as we saw in the case of glucose, some energy has to be used up before getting to the Krebs cycle, even for proteins and fats.

Black letters A through I are the various steps; green letters are the B vitamins required for those steps

Each step of the Krebs cycle requires enzymes and contributes to, directly or indirectly, the production of ATP. And for those enzymes to function, they need the B vitamins — B1 (thiamin or thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), and B12 (cobalamin).

Animal derived foods are the major sources of vitamin B12, making vegetarians and vegans particularly susceptible to B12 deficiency. Normal microbes that are present in your intestines also make some amounts of B12 and influence the general well-being of the digestive system, which then affects your overall health. These normal microbes are destroyed when you take medications that affect your digestive system, including chemotherapeutic agents for most cancers. Antibiotics also destroy the lining of the digestive system. Consequently, it is extremely important to replenish yourself with foods which provide the necessary vitamins, or vitamin supplements. But it is important to remember that for your body to utilize the B12 you take, your stomach also needs to be healthy — cells in the stomach produce a protein that attaches to the B12 you swallow, and safely shepherds it through the intestines from where it will finally exit into the bloodstream, and reach all the tissues in your body.

Dorothy Hodgkin. Cobalamin (B12)

Dorothy Hodgkin was a British biochemist who won the Nobel Prize in Chemistry in 1964, for determining the chemical structure of vitamin B12. Until her research, B12 deficiency was typically addressed using extracts from crushed beef, lamb, and pig livers. Armed with her findings, researchers were able to devise methods to produce B12 in the laboratory, thus allowing foods to be fortified with this vitamin, as well as manufacturing the vitamin for use both in the injectable and the oral form.

To be sure, Vitamin B12 is not a panacea for inexplicable fatigue and pains, but it is a key component of so many critical biochemical processes — the Krebs cycle is just one example — that it would be foolhardy to ignore addressing its deficiency. With an increasing number of people opting to forego meat in their diets, being ahead of the B12 deficiency curve by taking B12 supplements is as easy as taking a daily B12 tablet. Just do it!



Deepti Pradhan

Employed at Yale University, Deepti is primarily a scientist & patient advocate. She runs Tilde Cafe, a forum to make science accessible (www.tildecafe.org)