The Healthspan Map · Nutrient
Vitamin B12
Compiled by Aamir Malik, PhD, Professor of Neuroengineering at Brno University of Technology, from published studies. He is a researcher, not a physician. Last updated 21 August 2026.
Linked to getting too little
| Condition or system | Direction | Strength | Evidence type | What was found | Source |
|---|---|---|---|---|---|
| Anemia | Eat enough of | Strong | Established clinical | B12 deficiency is one of the two most common causes of megaloblastic anemia. | Megaloblastic anemia (B12/folate) (opens in a new tab) |
| Anxiety | Eat enough of | Emerging | Review / narrative | B12 deficiency is linked to neuropsychiatric symptoms incl. anxiety; repletion helps. | Neuropsychiatric B12-deficiency case report; Young 2019 (opens in a new tab) |
| Balance & falls risk | Eat enough of | Moderate | Established clinical | B12 deficiency causes peripheral neuropathy and gait/proprioception impairment — recognised contributors to falls. | Falls risk factors (StatPearls) (opens in a new tab) |
| Brain fog & memory | Eat enough of | Strong | Established clinical | Deficiency causes cognitive decline, memory loss and dementia, plus psychiatric changes; raised homocysteine is a dementia risk factor. | NIH ODS / SCD literature – Vitamin B12 (opens in a new tab) |
| Brain fog & memory | Eat enough of | Strong | RCT / meta-analysis | Deficiency causes cognitive decline, memory loss and dementia, plus psychiatric changes; raised homocysteine is a dementia risk factor. | Effects of Vitamin B12 Supplementation on Cognitive Function, Depressive Symptoms, and Fatigue, Nutrients 2021 (opens in a new tab) |
| Chronic fatigue / low energy | Eat enough of | Strong | Established clinical | B12 is essential for oxygen transport and neuronal function; deficiency causes fatigue and macrocytic anaemia. | Micronutrients for energy/fatigue review (Tardy 2020) (opens in a new tab) |
| Depression / low mood | Eat enough of | Moderate | Established clinical | Deficiency causes depression, irritability and, rarely, psychosis. | NIH ODS – Vitamin B12 (opens in a new tab) |
| Insomnia / poor sleep | Eat enough of | Emerging | Cohort / observational | Vitamin B12 supports circadian/sleep-wake regulation; low B12 has been correlated with poorer sleep quality. | B12 & sleep-wake literature (opens in a new tab) |
| Muscle & joint pain / weakness | Eat enough of | Moderate | Systematic review | Vitamin B12 supports neuromuscular function; deficiency contributes to weakness and impaired muscle performance. | Nutritional supplements & sarcopenia (opens in a new tab) |
| Peripheral neuropathy | Eat enough of | Strong | RCT / meta-analysis | B12 deficiency causes nerve degeneration; supplementation reduces neuropathic symptoms and pain in diabetic neuropathy. | B12 & diabetic neuropathy meta (opens in a new tab) |
| Reproductive & sexual health | Eat enough of | Emerging | Review / narrative | Vitamin B12, via one-carbon metabolism with folate, supports spermatogenesis and sperm DNA integrity. | Diet & men’s fertility (Fertil Steril 2018) (opens in a new tab) |
| Skin, hair, nails & wound healing | Eat enough of | Emerging | Review / narrative | Vitamin B12 deficiency causes hyperpigmentation, nail changes and hair changes. | B12 & skin/nails (opens in a new tab) |
| Stress | Eat enough of | Emerging | RCT / meta-analysis | B-vitamin supplementation (>=3 B-group incl. B6/B12/folate) produces a small but significant reduction in stress (SMD 0.23). | Young et al. 2019, Nutrients (opens in a new tab) |
| Thyroid dysfunction | Eat enough of | Emerging | Review / narrative | B12 is commonly low in autoimmune thyroid disease (pernicious-anemia overlap); repletion supports Hashimoto’s patients. | Micronutrients & autoimmune thyroid review (PMC12372124) (opens in a new tab) |
| Tinnitus | Eat enough of | Moderate | Review / narrative | Higher vitamin B12 intake is associated with lower tinnitus odds; deficiency can demyelinate auditory nerve fibers. | Diet & tinnitus (opens in a new tab) |
| Vision problems | Eat enough of | Emerging | Review / narrative | B12 deficiency contributes to homocysteine-related AMD risk and nutritional optic neuropathy. | Retinal/ocular supplements review (PMC9710404) (opens in a new tab) |
| Weak immunity & chronic inflammation | Eat enough of | Moderate | Review / narrative | Vitamin B12 supports lymphocyte numbers and NK-cell activity. | B12 & immune cells (opens in a new tab) |
Linked to getting too much
| Condition or system | Direction | Strength | Evidence type | What was found | Source |
|---|---|---|---|---|---|
| Anxiety | Don't overdo | Emerging | Established clinical | High-dose B12 produced anxiety, akathisia and insomnia, resolving after stopping; confounded by underlying deficiency. | Cleveland Clinic — High B12 Levels (symptoms include anxiety) (opens in a new tab) |
| Headache & migraine | Don't overdo | Moderate | Established clinical | B12 has NO official UL, but chronic megadosing (supplements ~500-1,000 mcg = 200-400x the 2.4 mcg RDA) overwhelms excretion; a documented case links high-dose B12 to headache and insomnia, resolving ~2 weeks after stopping. (Flagship of the 4x-RDA practical-ceiling rule.) | Case report (PubMed 31018715) – high-dose B12 (opens in a new tab) |
| Insomnia / poor sleep | Don't overdo | Emerging | Cohort / observational | Very high B12 (e.g., high-dose injections) has been associated with insomnia and altered sleep-wake timing. | B12 & sleep-wake literature (opens in a new tab) |
The Healthspan Map is part of Fix the Floor, a book by Aamir Malik. About the book