Vitamin B12 is not made by plants or animals, but by microbes blanketing the earth. We presumably used to get B12 when we drank out of a mountain stream or sipped water from a well, based on studies showing vegetarians in developing countries who drink purified water appear to be at higher risk. Now, we typically chlorinate our water supply to kill off any bacteria. So, most of us don’t get a lot of B12 in our water anymore, but we don’t get a lot of cholera, either. That’s a benefit of living in a much more sanitary world. Vegetarians living in slums in lesser developed regions appear to have fewer B12 problems, though. Basically, the more hygienic our meals, the less B12 we get. Our fellow great apes, like gorillas, get all the B12 they need eating their own feces. I prefer supplements. So, how much should we get, which type is best, and how can we tell if we have a B12 deficiency?

The Benefits of Vitamin B12

We cannot mess around with getting vitamin B12. If we don’t get enough, we may face a wide range of disorders of the gut, blood, brain, and nervous system.

Many case reports detail ways B12 can be life-changing. For instance, a 47-year-old woman had a five-year history of psychosis. She had been treated with antipsychotic drugs and was cognitively impaired and reported visual hallucinations. After her mother revealed that the patient had been following a strict vegan diet for seven years, vitamin B12 supplementation was started and her symptoms went away. She had lost years of her life lost in a psychotic haze—apparently just because she didn’t want to take a supplement.

Vitamin B12 supplementation is mandatory for anyone eating plant-based diets and, as I’ll discuss later, for every one of us from age 65.

Vitamin B12 Deficiency: Symptoms and Treatment

As I discuss in my video The Symptoms of Vitamin B12 Deficiency, it can cause everything from abdominal distention and chronic diarrhea to shortness of breath and swollen, red, painful feet. It can also cause Parkinson’s syndrome–like symptoms, skin darkening (that resolved with supplementation), and bilateral useless hand syndrome, a condition I had never heard of before.

Being deficient in B12 may also manifest in a variety of neurological symptoms—for example, numbness and tingling in the hands and feet, muscle cramps, dizziness, cognitive disturbances, difficulty walking, and erectile dysfunction—as well as fatigue and such psychiatric symptoms as depression along with psychosis.

How can B12 deficiency be treated? Either with B12 supplements or B12-fortified foods.

Suggested Vitamin B12 Dosage

The official position of associations and governmental agencies is categorical and unequivocal: Supplementation of vitamin B12 is required for anyone on a vegetarian diet—even when consuming eggs and dairy—and I would extend that to include flexitarians eating only a few servings of meat a week.

Who else should ensure they have a regular, reliable source of vitamin B12 by supplementing their diet with B12 supplements or B12-fortified foods? Those who’ve had bariatric surgery (which can sometimes impair absorption), those eating plant-based diets, and everyone from the age of 65.

As I discuss in my video The Optimal Vitamin B12 Dosage for Adults, adults younger than 65 should take at least one 2,000 mcg (µg) supplement once a week, ideally as a chewable, sublingual, or liquid supplement taken on an empty stomach, or at least one 50 mcg (µg) daily supplement. As we age, our ability to absorb vitamin B12 may decline. So, for those 65 and older, the supplementation should probably be increased up to 1,000 mcg (µg) each day, as I discuss in my video The Optimal Vitamin B12 Dosage for Kids, Pregnancy, and Seniors.

Pregnant and breastfeeding women can just follow my 50 mcg (µg) a day recommendation for nonpregnant adults or take 2,000 mcg (µg) a week, perhaps split into two doses to boost absorption. After infants are weaned, they can start on 5 mcg (µg) a day. From ages 4 through 10, kids can take half the adult dose of 25 mcg (µg) a day, then they can take 50 mcg (µg) a day or 2,000 mcg (µg) a week from age 11.

Note that these doses are specific to cyanocobalamin, the preferred supplemental form of vitamin B12. (I discuss cyanocobalamin versus methylcobalamin below.)

The Best Food Sources of Vitamin B12

If you need supplemental B12 but don’t want to take supplements, you must rely on B12-fortified foods––eating three separate servings of B12-fortified foods a day, each ideally containing at least 190 percent of the “Daily Value” on the product’s nutrition facts label. As I discuss in my video The Healthiest Food Sources of Vitamin B12, B12-fortified nutritional yeast is a common food source, and there are all sorts of other B12-fortified options on the market, including plant-based meats and milks, breakfast cereals, and even energy drinks. 

The Worst Food Sources of Vitamin B12

What about various algae-type products, like spirulina, which are advertised as natural vitamin B12 sources? Not only do they not actually contain B12 that’s useable for humans, they may contain B12 analogues—look-alike molecules that can even block your absorption of real B12!

Can Vitamin B12 Cause Side Effects?

You don’t have to worry about taking too much vitamin B12. It’s water-soluble. So, at worst, you’ll just end up with more expensive pee. Injectable forms, though, can trigger acne.

Methylcobalamin vs. Cyanocobalamin

There are two main types of vitamin B12: methylcobalamin, marketed as methyl B12, and cyanocobalamin, typically marketed as just vitamin B12. Methylcobalamin is more expensive so it must be better, right? Wrong.

As I discuss in my video The Best Type of Vitamin B12: Cyanocobalamin or Methylcobalamin, cyanocobalamin is the most used form, thanks to its high stability. Methylcobalamin is less stable and particularly susceptible to being destroyed after exposure to light.

The one major exception may be kidney failure, though. Methylcobalamin may be better for those with impaired kidney function. It’s been speculated that oral methylcobalamin or injected hydroxycobalamin may also be preferable in smokers, though it has yet to be confirmed.