Several readers asked me about an article that appeared on the Vegan Mainstream website linking oral contraceptive use to vitamin B12 deficiency. The writer, who was depending in part on greens and sea veggies for vitamin B12 (somebody bring me my smelling salts, please) ended up with a B12 deficiency. Unable to reverse the deficiency with supplements, she finally was able to bring her blood levels back up after a doctor advised her to discontinue using oral contraceptives.

I can’t comment on this particular situation, but I can comment on the conclusion made in the article that “a vegan on birth control is a recipe for B12 trouble.”

The research does suggest that oral contraceptive use is associated with lower blood levels of vitamin B12 in many women (the vast majority of whom are not vegan, of course.) And, in omnivores using oral contraceptives, taking B12 supplements often doesn’t raise blood levels of this vitamin. But blood levels of B12 are not always a good indicator of actual nutrient status. Levels can sometimes be high even when a person is, in fact, deficient. And, in the case of oral contraceptive users, it appears that low blood levels of B12 may not always translate to deficiency.

Better indicators of B12 status are blood levels of compounds that require vitamin B12 for their metabolism. In vitamin B12 deficiency, levels of two compounds—methylmalonic acid and homocysteine—are elevated. In the studies of oral contraceptive users, even when serum B12 levels are low, these other more important changes don’t seem to occur.

Researchers believe that the lower blood levels of B12 are related to a decrease in certain proteins that bind B12—but that this doesn’t affect the amount of B12 being delivered to tissues. So while blood levels are low, B12 status is often fine.

This may not be the final word on oral contraceptives and vitamin B12, but it’s where the research stands right now. In their discussion of factors affecting vitamin B12 requirements, the Food and Nutrition Board (the U.S. government group that establishes nutrient recommendations) doesn’t even mention oral contraceptives. Of course, this doesn’t mean it’s impossible to develop a B12 deficiency while using oral contraceptives. Anyone who experiences a drop in vitamin B12 levels should talk with their doctor to decide if further testing is warranted.

But, if there is an issue here at all, it’s not really a vegan one. Given her lack of knowledge about sources of vitamin B12, it’s reasonable to believe that the writer of the Vegan Mainstream article had a true B12 deficiency. But, the problem was inadequate information about how to meet vitamin B12 needs on a vegan diet. Even if oral contraceptives were shown to impact vitamin B12 status, this shouldn’t be any more of a problem for vegans who take appropriate supplements than for anyone else.

So no, it isn’t true that “a vegan on birth control is a recipe for B12 trouble.” It is true that a vegan who doesn’t take adequate supplements is a recipe for B12 trouble.

As a quick refresher, any of the following strategies should meet the vitamin B12 needs of vegan adults:

  • Two servings per day of foods that are fortified with 1.5 or more micrograms of B12, OR
  • 25 micrograms or more of a chewable or sublingual B12 supplement every day, OR
  • 1,000 micrograms from a chewable or sub-lingual supplement twice per week.

Some references on oral contraceptive use and vitamin B12:

Shojania AM, Wylie B. The effect of oral contraceptives on vitamin B12 metabolism. Am J Obstet Gynecol 1979;135(1):129-34.

Gardyn J, Mittelman M, Zlotnik J, Sela BA, Cohen AM. Oral contraceptives can cause falsely low vitamin B(12) levels. Acta Haematol 2000;104(1):22-4.

Carmel R. Mild transcobalamin I (haptocorrin) deficiency and low serum cobalamin concentrations. Clin Chem 2003;49(8):1367-74

Riedel B, Nexo E, et al. Effects of oral contraceptives and hormone replacement therapy on cobalamin status. J Inherit Metab Dis 2003;23(supl):127

Rosenthal HL, Wilbois RP. Influence of oral contraceptive agents on vitamin B12 absorption and plasma level. Fed Proc 1975:34:905.

Sutterlin MW, Bussen SS, Rieger L, Dietl J, Steck T. Serum folate and Vitamin B12 levels in women using modern oral contraceptives (OC) containing 20 microg ethinyl estradiol. Eur J Obstet Gynecol Reprod Biol 2003;107(1):57-61.

Lussana F, Zighetti ML, Bucciarelli P, Cugno M, Cattaneo M. Blood levels of homocysteine, folate, vitamin B6 and B12 in women using oral contraceptives compared to non-users. Thromb Res 2003;112(1-2):37-41.

Vakur Bor, M. Do we have any good reason to suggest restricting the use of oral contraceptives in women with pre-existing vitamin B12 deficiency? Eur J Obstet Gyn Repr Biol 2004;115:240-241.