Say you decide to eat no animal products, which are the primary source for vitamin B12 in the human diet. How long will it take for your B12 status to fall below normal?1
Here's a study from the USDA archives:
Vitamin B12 Studies In Total Vegetarians (Vegans), Journal of Nutritional Medicine, 1994
I can only see the abstract and it's difficult to follow the group(s) they studied, but they describe:
"In 10 who changed from a lacto-ovo-vegetarian (LOV) diet to a TVD,2 the mean serum B12 level dropped 35% from 415 +/- 187 to 268 +/- 75 pg ml-1 p<0.005) 2 months after starting the TVD. ... Serum B12 levels decreased noticeably within 2 months on a [vegan diet]."So, after 2 months, the group's average was hovering close to what the IOM considers a lower limit. After a year:
"61% of those on the [vegan diet] for 1 year or more had serum B12 levels below normal."Looks like they used 200 pg/ml as the cutoff for normal. All well and good but the IOM says, "a serum B12 value above the cutoff point does not necessarily indicate adequate B12 status," because "as deficiency develops, serum values may be maintained at the expense of B12 in the tissues."
They also looked at the prevalence of low B12 status in vegans. In 78 vegans, 47 were below normal. Even the remaining 31 had levels only reaching 293 +/- 85.
Everyone is different. Some people may be very efficient at reabsorbing any B12 they secrete into the small intestine via bile.3 But reabsorption is not 100%. And there is some loss of B12 after this point anyway, from cells that break off in the large intestine. Without some B12 input, there will be net loss over time. And anyone with absorption problems in the area of their distal small intestine where B12 is taken up (or if this part of the intestine is absent from, say, cancer or Crohn's surgery), and anyone with inflammatory issues in the stomach where intrinsic factor (IF) is secreted (IF assists in B12 absorption) will most definitely face B12 deficiency without some treatment.
So, how long will it take to fall below normal? From this data, somewhere between a few months to a few years depending on the health of the GI tract.
If I was eating a vegan diet, I would definitely supplement with vitamin B12, and/or eat B12 fortified food.
One more point from this study, about supplementing:
"The serum B12 level of seven of 16 adults with a low serum B12 who chewed a 100 microgram tablet of B12 once a week for 6 weeks increased by 150%, whereas the serum B12 level increased by only 12% in the nine who gulped down the tablets (with water)."
2 TVD: Total Vegetarian Diet, i.e. Vegan Diet
3 How much we lose in bile depends in part on how much fat we eat, since bile is secreted to emulsify dietary fat. Still, this is not a lot, maybe 0.5 to 1 mcg/day say the IOM.
5 comments:
Many vegans refuse to supplement with B12 in any form.
Why?
Because they are more of the mindset that a total whole-foods plant-based diet is the most natural healthy diet ever and that anything unnatural should be avoided. I know there’s a recent B12 study on German vegans (sorry, too lazy to search for it) where they did pretty poorly in their B12 status, but German vegans in particular would lean towards this idea of living food and naturalness in diet.
There’s also the less health-oriented ethical vegans who feels that it’s some sort of conspiracy (or misunderstanding) to make veganism more difficult than it is. Often these are long-term vegans who never (knowingly) supplemented and never had any (known) issues or know of any vegan associates who had any problems.
Regarding this:
"The serum B12 level of seven of 16 adults with a low serum B12 who chewed a 100 microgram tablet of B12 once a week for 6 weeks increased by 150%, whereas the serum B12 level increased by only 12% in the nine who gulped down the tablets (with water)."
Jack Norris, who is fairly conservative with his recommendations meaning that he errs on the side of caution, has looked into the discrepancy between oral B12 and swallowing tables and feels that it doesn’t make much of a difference so long as the supplementation happens.
http://goo.gl/9HhJv
I’m not sure if he knows about the 1994 paper you cited, but he refers to a 2003 paper in his post.
I don’t cite him as my vegan diet guru or anything, but he is far more interested in keeping vegans healthy, than he is in offering that veganism is the healthiest diet ever. It’s an important distinction.
Personally, my partner (also vegan) and I have had a couple blood tests and B12 levels have been fine so we’ll just keep doing what we’ve been doing, basically a combination approach that I don’t think about because it’s just worked into my eating patterns. I’ve been a non-meater for over a decade, so if I wasn’t low by now, it probably won’t happen all of a sudden.
I’m less concerned about all out B12 deficiency per se which seems more individualized , and more with the elevated homocysteine levels that can arise from low B12 levels. A plant-based diet is supposed to help reduce heart diseases risk factors, notsense in undermining that by not getting adequate B12. There’s no known risk of taking B12, no demonstrated toxicity, but certainly benefits (reduced risks) to doing so, even if someone is not vegan.
The unnaturalness of supplementing B12 doesn’t bother me (naturalistic fallacy) though is some respects I find myself aligned with you (Bix) in keeping pill popping to a minimum mostly because vitamins haven’t been reliably proven to promote health, but vitamins most certainly do prevent deficiencies and most of the population is supplementing with something whether they know it or not (iodine, vitamin A & D, folate, etc.)
With that said, I’m fairly sure that the billion-dollar industry of supplements isn’t being propped up by the small fraction of vegan customers. Even ancestral health advocates (paleo, locavores, etc.) have laundry lists of supplements they advise their practitioners to take even though their entire shtick is “naturalness” of diet.
One final note. The B12 in supplement form isn’t synthetic anyway. It can be synthesized (earned a Nobel prize for someone doing so), but that’s expensive. The B12 in supplements is “farmed” from bacteria, so it’s a matter of preference whether you want your B12 farmed from animals, in most cases whose diets are supplemented with B12 anyway (yes, even small farms), or farmed from bacteria where the ethical and environmental hand wringing is a lot lower.
Jack Norris really does a superb job with B12. I read this article of his off and on:
http://veganhealth.org/articles/vitaminb12
Actually, according to the Institute of Medicine, the group that sets the RDAs, everyone over 50, vegan or not, should supplement with B12, owing to decreased absorption as we age.
Gorillas get their vitamin B12 from termites and other creepy crawlies. They might also get some B12 from the bacteria in their own intestines, through the fecal-oral route. Gorillas are not meticulous about washing their hands.
http://wheredogorillasgettheirprotein.blogspot.com/2010/01/where-do-gorillas-get-their-vitamin-b12.html
I saw sites that say you should lick the dirt off vegetables to get B12. Tell you right now, ain't gonna happen. I'll take the pill thank you.
Anyone know what kind to buy?
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