In a new study from the United Kingdom, researchers found that more than half of vegan men were deficient in vitamin B12 based on their serum levels. The findings are part of the EPIC-Oxford study and will be published in the European Journal of Clinical Nutrition.

The researchers looked at diets and serum levels of B12 in 226 omnivores, 231 vegetarians and 232 vegans. Mean serum B12 levels in vegans were 33% lower than in the vegetarians and 57% percent lower than in the omnivores.

In addition, the vegans had much higher serum levels of folate—not surprising since vegan diets are typically high in this nutrient. Since folate can mask B12-deficiency anemia, there are concerns about diets that are low in B12 and high in folate.

One especially unfortunate finding: Only 19% of the vegan men said they took vitamin B12 supplements. And surprisingly, their serum levels of vitamin B12 were no higher than those of vegan men who didn’t take supplements.

Why are some vegans not getting adequate vitamin B12? Most likely there continues to be some reluctance among vegans regarding B12 supplements. But there is also an ongoing problem of inadequate advice within the vegan community. According to the EPIC-Oxford researchers, “[…] it may be necessary to improve the understanding of the need to regularly consume supplements containing adequate amounts of the active form of vitamin B12.”

Although most vegan advocates, especially within the animal rights community, provide good information about vitamin B12 nutrition, there are still some popular sources of information that fall short. For example, the book The China Study, offers up this advice “If you do not eat any animal products for three years or more, or are pregnant or breastfeeding, you should consider taking a small B12 supplement on occasion.” (Emphasis added) Other equally popular vegan advocates have suggested that a B12 supplement isn’t necessary until after three years on a vegan diet and that, at that point, a small supplement will do.

But does the average vegan start out with a 3-year supply of vitamin B12? Those who were eating a lacto-ovo vegetarian diet or a “flexitarian” type of diet before going vegan could very well have much smaller stores of B12. And research suggests that blood levels can decline fairly rapidly in just months when B12 intake is low. Furthermore, if you wait until stores are depleted and blood levels have dropped, it is unlikely that a “small” and “occasional” supplement is going to restore B12 to healthful levels.

Taking a B12 supplement is the easiest thing in the world. It doesn’t make sense to wait until stores diminish or you are approaching deficiency before you start to supplement. And it certainly is not good vegan advocacy to promote inadequate advice about vitamin B12.

From the day you go vegan, you should begin to supplement with vitamin B12 or use a variety of fortified foods. Absorption of B12 drops dramatically as the dose goes up, so if you are supplementing just once a day, you need a fairly high amount—at least 10 ug per day. (If you have been vegan for a while and haven’t been supplementing, you may need much more.) It’s important to choose a supplement that can be chewed or allowed to dissolve beneath the tongue.

And when new (or experienced) vegans ask about vitamin B12, veganhealth remains the best and most reliable source of information.