Uploaded November 2025 | Updated September 2026, 2 weeks ago
For those eating plant-based diets, encouragement of vitamin B12 supplementation cannot be overemphasized. Surprisingly, there are no consensus clinical guidelines on preventing, diagnosing, and treating B12 deficiency.
This is the first video in a five-part series on vitamin B12. Stay tuned for:
• The Best Way to Test for Vitamin B12 Deficiency (nutritionfacts.org/video/the-best-way-to-test-for-vitamin-b12-deficiency)
• The Best Source of Vitamin B12: Supplements, Shots, or Fortified Foods? (nutritionfacts.org/video/the-best-source-of-vitamin-b12-supplements-shots-or-fortified-foods)
• How Much Vitamin B12 Do We Need Each Day? (nutritionfacts.org/video/how-much-vitamin-b12-do-we-need-each-day)
• Are Large Weekly Doses of Vitamin B12 Safe? (nutritionfacts.org/video/are-large-weekly-doses-of-vitamin-b12-safe)
For more on vitamin B12, check out the topic page (nutritionfacts.org/topics/vitamin-b12/).
New subscribers to our e-newsletter always receive a free gift. Get yours here: nutritionfacts.org/subscribe/.
Have a question about this video? Leave it in the comment section at nutritionfacts.org/video/how-long-does-it-take-to-become-vitamin-b12-deficient-and-what-are-the-symptoms and someone on the NutritionFacts.org team will try to answer it.
Want to get a list of links to all the scientific sources used in this video? Click on Sources Cited at nutritionfacts.org/video/how-long-does-it-take-to-become-vitamin-b12-deficient-and-what-are-the-symptoms. You’ll also find a transcript and acknowledgements for the video, my blog and speaking tour schedule, and an easy way to search (by translated language even) through our videos spanning more than 2,000 health topics.
Thanks for watching. I hope you’ll join in the evidence-based nutrition revolution!
-Michael Greger, MD FACLM
Captions for this video are available in several languages; you can find yours in the video settings. View important information about our translated resources: nutritionfacts.org/translations-info
NutritionFacts.org
• Subscribe: nutritionfacts.org/subscribe
• Donate: nutritionfacts.org/donate
• Podcast : nutritionfacts.org/audio
• Books: nutritionfacts.org/books
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• Twitter: twitter.com/nutrition_facts
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For those eating plant-based diets, encouragement of vitamin B12 supplementation cannot be overemphasized. Surprisingly, there are no consensus clinical guidelines on preventing, diagnosing, and treating B12 deficiency.
This is the first video in a five-part series on vitamin B12. Stay tuned for:
• The Best Way to Test for Vitamin B12 Deficiency (nutritionfacts.org/video/the-best-way-to-test-for-vitamin-b12-deficiency)
• The Best Source of Vitamin B12: Supplements, Shots, or Fortified Foods? (nutritionfacts.org/video/the-best-source-of-vitamin-b12-supplements-shots-or-fortified-foods)
• How Much Vitamin B12 Do We Need Each Day? (nutritionfacts.org/video/how-much-vitamin-b12-do-we-need-each-day)
• Are Large Weekly Doses of Vitamin B12 Safe? (nutritionfacts.org/video/are-large-weekly-doses-of-vitamin-b12-safe)
For more on vitamin B12, check out the topic page (nutritionfacts.org/topics/vitamin-b12/).
New subscribers to our e-newsletter always receive a free gift. Get yours here: nutritionfacts.org/subscribe/.
Have a question about this video? Leave it in the comment section at nutritionfacts.org/video/how-long-does-it-take-to-become-vitamin-b12-deficient-and-what-are-the-symptoms and someone on the NutritionFacts.org team will try to answer it.
Want to get a list of links to all the scientific sources used in this video? Click on Sources Cited at nutritionfacts.org/video/how-long-does-it-take-to-become-vitamin-b12-deficient-and-what-are-the-symptoms. You’ll also find a transcript and acknowledgements for the video, my blog and speaking tour schedule, and an easy way to search (by translated language even) through our videos spanning more than 2,000 health topics.
Thanks for watching. I hope you’ll join in the evidence-based nutrition revolution!
-Michael Greger, MD FACLM
Captions for this video are available in several languages; you can find yours in the video settings. View important information about our translated resources: nutritionfacts.org/translations-info
NutritionFacts.org
• Subscribe: nutritionfacts.org/subscribe
• Donate: nutritionfacts.org/donate
• Podcast : nutritionfacts.org/audio
• Books: nutritionfacts.org/books
• Shop: drgreger.org
• Facebook: facebook.com/NutritionFacts.org
• Twitter: twitter.com/nutrition_facts
• Instagram: instagram.com/nutrition_facts_org
