Uploaded November 2025 | Updated September 2026, 1 week ago
A diagnosis of B12 deficiency should not be dismissed based solely on a single measurement of B12 levels in the blood. For classic symptoms of B12 deficiency, a therapeutic trial of B12 supplementation should be considered even if laboratory values are normal.
This is the second video in a five-part series on vitamin B12. If you missed the previous one, check out How Long Does It Take to Become Vitamin B12-Deficient and What Are the Symptoms? (nutritionfacts.org/video/how-long-does-It-take-to-become-vitamin-b12-deficient-and-what-are-the-symptoms). Stay tuned for:
• 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/the-best-way-to-test-for-vitamin-b12-deficiency 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/the-best-way-to-test-for-vitamin-b12-deficiency. 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
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A diagnosis of B12 deficiency should not be dismissed based solely on a single measurement of B12 levels in the blood. For classic symptoms of B12 deficiency, a therapeutic trial of B12 supplementation should be considered even if laboratory values are normal.
This is the second video in a five-part series on vitamin B12. If you missed the previous one, check out How Long Does It Take to Become Vitamin B12-Deficient and What Are the Symptoms? (nutritionfacts.org/video/how-long-does-It-take-to-become-vitamin-b12-deficient-and-what-are-the-symptoms). Stay tuned for:
• 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/the-best-way-to-test-for-vitamin-b12-deficiency 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/the-best-way-to-test-for-vitamin-b12-deficiency. 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
