Vitamin B12

Vitamin B12
Vitamin name	Cobalamin
Chemical formula	C₆₃H₈₈CoN₁₄O₁₄P
Solubility	Water-soluble
Discovery year	Late 1940s (isolated); structure determined ~10 years later via X-ray crystallography
Daily requirement (RDA)	2.4 mcg for adults
Upper limit	N/A (no known toxicity from food/supplements)
Rich food sources	Liver, beef, fish, shellfish, eggs, dairy,

Introduction

Vitamin B12 is a water-soluble vitamin and one of the most critical nutrients for daily consumption due to its unique absorption characteristics. Unlike most vitamins that can be "stocked up" over longer periods, B12 has a strict absorption cap that limits how much can be taken in at any given meal, making consistent dietary intake essential.

Structure/Chemical properties

B12 exists in several forms:

• Hydroxocobalamin - The most common form found naturally in food
• Methylcobalamin - A biologically active form; the amount of methyl in this form is very small
• Adenosylcobalamin - Found in animal tissues
• Cyanocobalamin - A synthetic form bound to cyanide, not found in the food supply

Function/Mechanism of Action

Carotene to vitamin A conversion

B12 is crucial for converting carotene into vitamin A. Ray Peat describes a case of a young man who was extremely sick with practically no vitamin A in his blood but extremely high carotene, which was blocking all of his hormones. In his case, all it took was one dose of vitamin B12, and within a week his symptoms had gone and his vitamin A level was normal (Ray Peat, Foundational Hormones interview).

"Vitamin B12 happens to be crucial for turning carotene into vitamin A." - Ray Peat

Thyroid and steroid support

The relationship between B12 and thyroid is critical. You convert carotene to vitamin A if you have vitamin B12 in proportion to how active your thyroid hormone is. If you are getting more carotene than your vitamin B12 and thyroid can handle, the carotene accumulates and turns off thyroid function (Ray Peat, Effects of Stress and Trauma).

"The whole cholesterol conversion process goes bad when you're poisoned with keratin [carotene], and vitamin B12 is needed to break the keratin molecule into two vitamin A molecules." - Ray Peat

Homocysteine regulation

A diet rich in folic acid, B12, B6, and good thyroid function helps safely lower homocysteine levels. Milk, eggs, and orange juice are helpful foods for this purpose .

Medical uses/Effects

Deficiency in vegetarians/vegans

B12 is a primary concern for those following plant-based diets. Ray notes that vegetarian diets, unless they include B12 shots, probably do not have enough B12. He adds that people think spirulina or spinach provide adequate B12, but these are "nowhere near as effective as perhaps having egg yolks".

Potatoes and mushrooms can provide most nutrients except vitamin A and vitamin B12, making these the limiting factors for vegetarians.

More in Vegetarianism

High B12 and bacterial overgrowth

Ray generally does not recommend B12 supplementation because we can make it in our intestine. However, he has seen many people with twice the normal amount of B12, which indicates bacterial overgrowth in the intestine rather than a benefit:

"The B12 isn't hurting them, but when it's so high without a supplement, that means that their bacteria are going wild." - Ray Peat

This overgrowth is caused by slow digestion. When thyroid function is good, the body produces exuberant amounts of stomach acid and pancreatic enzymes so that germs cannot survive. The small intestine should be sterile all the way down to the colon.

More in SIBO

Hair graying

Deficiency of vitamin B12 (along with hypothyroidism, calcium, and vitamin D deficiency) has been linked to premature hair graying. The research suggests that hair pigmentation loss caused by nutritional deficiencies could be reversible.

More in Grey hair

Side/Adverse effects

Elevated B12 without supplementation

Extremely high B12 levels in those not supplementing may indicate small intestinal bacterial overgrowth (SIBO) and should be investigated as a marker of poor digestive function rather than ignored.

Folic acid and B12 concerns

Folic acid and vitamin B12 both have positive correlations with cancer in some data, which is one reason he does not strongly advocate for their isolated supplementation.

Dosing

Food sources

Liver: Any kind of liver (chicken, beef, fish) is a great source of B12 along with vitamins A, D, K, and other nutrients. However, liver is very high in iron and phosphate, so Ray recommends no more than one good serving (about 4 ounces) per week to avoid chronic overload of concentrated nutrients.

Dairy: Pasteurization reduces the content of vitamin B2, B12, and folic acid very slightly, but raw milk from a clean dairy has slightly more

Eggs: A good source of B12, especially the yolks.

Milk, cheese, and eggs are helpful foods for B12 status and for lowering homocysteine when combined with good thyroid function .

Considerations

Ray generally does not recommend B12 supplementation because of intestinal synthesis. Any small source of B12 can keep a vegetarian in good health as long as they avoid too many plant toxins.

More in Vegetarianism

If supplementation is used, the amount of methyl in methylcobalamin is so tiny that reactions are more likely allergic than due to the methyl group itself. Folic acid is also allergenic, and different manufacturing processes could account for different reactions to different products.

Relationship to thyroid

B12 requirements are connected to metabolic rate. Adequate thyroid function is necessary to use B12 properly for converting carotene to vitamin A and for supporting steroid hormone production. Supplementing B12 without addressing underlying hypothyroidism may not resolve deficiency symptoms.