English version in progress: interface and data are in English; some explanatory text is still in Chinese.
Vitamin B12
食物中的 B12 要先靠胃酸释放，再和胃里分泌的"内因子"结合，才能在小肠末端被吸收。
Full ranking Dose tool Products (6,218)
Key facts
Daily Value (US FDA)2.4 mcg
Tolerable Upper Intake Level (UL)—
Median（Per day）50 mcgP5 1.2 – P95 2,000
Products6,218
Sources: https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/ · FDA DV 2.4 mcg (https://www.fda.gov/food/nutrition-facts-label/daily-value-nutrition-and-supplement-facts-labels); pre-2016 DV [6] (https://www.federalregister.gov/documents/2016/05/27/2016-11867/food-labeling-revision-of-the-nutrition-and-supplement-facts-labels); no UL set; hard_high=50000 per serving (UL x10 or market maximum), hard_low=DV/1000
How it works：为什么有人吃了 B12 也吸收不好？
- 食物中的 B12 与蛋白质结合，需要胃酸和蛋白酶把它释放出来。补剂中的 B12 是游离的，不需要这一步。
- B12 与胃壁细胞分泌的内因子结合。
- 结合物在回肠末端被吸收。缺乏内因子（恶性贫血）的人吸收很差。
- B12 参与红细胞生成、神经功能和 DNA 合成。
Schematic only; positions and scale are not anatomical.
Limits and cautions：尚未设定 UL。长期服用二甲双胍或抑酸药可能降低 B12 吸收。
Sources：NIH ODS: VitaminB12 Fact Sheet for Health Professionals
Daily dose across products（mcg/day）
DV 2.4
0.48 mcglog scale · n=6,21812,000 mcg
Label data from official national databases and brand websites, as declared; not lab-verified.
Common forms
| Form | Products | Median | P5–P95 | Elemental fraction |
|---|---|---|---|---|
| Methylcobalamin | 2689 | 100 mcg | 2.4 – 1,000 | — |
| Cyanocobalamin | 2535 | 25 mcg | 1.2 – 2,800 | — |
| Adenosylcobalamin | 157 | 225 mcg | 25 – 3,000 | — |
| Hydroxocobalamin | 34 | 125 mcg | 4 – 2,000 | — |
Top ranked
| Rank | Brand | Product | Per day | Score |
|---|---|---|---|---|
| 1 | Swanson | Activated B12 Complex Natural Cherry Flavor | 2,000 mcg | 90.0 |
| 1 | The Vitamin Shoppe | Liquid Vitamin B12 1000 mcg | 1,000 mcg | 90.0 |
| 1 | The Vitamin Shoppe | Vitamin B12 Gummies 1000 mcg Raspberry | 1,000 mcg | 90.0 |
| 4 | International Vitamin Corporation | B12 2500 mcg | 2,500 mcg | 88.0 |
| 4 | The Vitamin Shoppe | B12 Methylcobalamin 1000 mcg Black Cherry | 1,000 mcg | 88.0 |
For information only; not medical advice. Talk to a doctor or pharmacist before starting or stopping any supplement.