B-Complex
The eight water-soluble B vitamins work as a cofactor network for energy metabolism and neurotransmitter synthesis. Deficiency in any one (B12, folate, B6) produces measurable cognitive symptoms.
What it is
B-complex refers to eight distinct vitamins: B1 (thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B7 (biotin), B9 (folate), and B12 (cobalamin). They function as coenzymes in ATP production, one-carbon metabolism, and neurotransmitter synthesis. Methylated forms (methylfolate, methylcobalamin, P-5-P) bypass MTHFR gene polymorphisms that affect roughly 30-40% of the population.
How it works
B1, B2, B3, B5 drive the Krebs cycle and electron transport chain (cellular ATP). B6, B9, B12 run the methylation cycle — which synthesizes serotonin, dopamine, norepinephrine, and myelin, and clears homocysteine. Elevated homocysteine from B-vitamin deficiency is an independent risk factor for brain atrophy and dementia.
What the research says
Evidence strength is ranked against the total body of peer-reviewed research, not marketing claims.
Who it helps
Vegetarians and vegans (B12 is animal-derived — deficiency is near-universal without supplementation). Adults over 50 (stomach acid declines, B12 absorption drops). People on metformin, PPIs, or oral contraceptives (all deplete B vitamins). Anyone with MTHFR C677T variant. People with elevated homocysteine on bloodwork.
Who should skip it
People with bipolar disorder — high-dose methylated B vitamins can precipitate hypomania in a subset of users. People with Leber's hereditary optic neuropathy (avoid cyanocobalamin). Start low if you suspect methylation sensitivity — 'overmethylation' from high B12/folate produces anxiety, insomnia, irritability.
Typical dose
A standard B-complex provides each B at 100-500% RDA. Look for: methylfolate (not folic acid), methylcobalamin or adenosylcobalamin (not cyanocobalamin), P-5-P (not pyridoxine HCl). B6 has a ceiling — doses above 100 mg/day long-term can cause peripheral neuropathy.
How to take it
Take with breakfast — B vitamins are water-soluble and can cause mild nausea on empty stomach, and they are mildly energizing (bad at night). Expect bright yellow urine from B2 — that is normal, not waste (riboflavin is just colored).
Common misuses
People take B6 at 200 mg 'because more is better' and develop neuropathy months later. People with MTHFR take folic acid, which they can't methylate, and it competes with methylfolate for receptors. People take B12 at night and can't sleep. People take cyanocobalamin, which requires the body to cleave a cyanide molecule — not dangerous but wasteful.
Where to buy
Browse B-Complex on Amazon
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