The Healthspan Map · Nutrient

Folate (B9)

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

Where a shortfall of Folate (B9) is linked: 19 sources.In the order the Map holds them: strongest evidence first. That is a statement about the evidence, not about what matters most.
Condition or system	Direction	Strength	Evidence type	What was found	Source
Anemia	Eat enough of	Strong	Established clinical	Folate 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	RCT / meta-analysis	B-vitamin supplementation aids stress/anxiety regulation; supports neurotransmitter synthesis.	Young et al. 2019, Nutrients (opens in a new tab)
Brain fog & memory	Eat enough of	Moderate	Cohort / observational	Low folate (especially with low B12) is associated with cognitive decline and higher Alzheimer risk.	Linus Pauling Institute; Huskisson et al. 2007 (opens in a new tab)
Brain fog & memory	Eat enough of	Moderate	Review / narrative	Low folate (especially with low B12) is associated with cognitive decline and higher Alzheimer risk.	Linus Pauling Institute — Folate (opens in a new tab)
Chronic fatigue / low energy	Eat enough of	Moderate	Review / narrative	Folate supports DNA synthesis and red-cell formation; deficiency contributes to fatigue and anaemia.	Micronutrients for energy/fatigue review (Tardy 2020) (opens in a new tab)
Depression / low mood	Eat enough of	Moderate	Established clinical	Deficiency causes neuropsychiatric symptoms including depression and cognitive impairment.	StatPearls – Folate (opens in a new tab)
Headache & migraine	Eat enough of	Emerging	Cohort / observational	Higher dietary folate intake is inversely associated with migraine frequency; evidence emerging.	Dietary B6/folate-migraine association (via food-migraine review 2024) (opens in a new tab)
Insomnia / poor sleep	Eat enough of	Moderate	Cohort / observational	Folate supports serotonin/melatonin formation; low folate intake is associated with short sleep.	Peuhkuri 2012; NHANES 2005-2016 (opens in a new tab)
Insomnia / poor sleep	Eat enough of	Moderate	Review / narrative	Folate supports serotonin/melatonin formation; low folate intake is associated with short sleep.	Peuhkuri et al., "Diet promotes sleep duration and quality", Nutr Res 2012 (opens in a new tab)
Peripheral neuropathy	Eat enough of	Emerging	Review / narrative	Folate deficiency contributes to peripheral neuropathy through the homocysteine/B-vitamin pathway.	Nutritional & toxic neuropathy (opens in a new tab)
Reproductive & sexual health	Eat enough of	Moderate	Cohort / observational	Folate supports ovulation, embryo quality and IVF success and (with zinc/B12 in one-carbon metabolism) spermatogenesis; preconception folate is standard for neural-tube prevention.	Female fertility nutrition review (PMC8634384) (opens in a new tab)
Skin, hair, nails & wound healing	Eat enough of	Emerging	Review / narrative	Folate deficiency causes cheilitis, hair depigmentation and mucocutaneous hyperpigmentation.	Folate & skin (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)
Tinnitus	Eat enough of	Emerging	Review / narrative	Folate supports nerve health and circulation relevant to the auditory system - emerging.	Diet & tinnitus (opens in a new tab)
Vision problems	Eat enough of	Emerging	Review / narrative	B-vitamin deficiency (folate/B12/B6) raises homocysteine, associated with AMD; folate supports optic-nerve/retinal health.	Retinal/ocular supplements review (PMC9710404) (opens in a new tab)
Weak immunity & chronic inflammation	Eat enough of	Moderate	Review / narrative	Folate is required for immune-cell proliferation and the Th1 response.	Folate & lymphocytes (opens in a new tab)
Reproductive & Developmental	Eat enough of	Strong	RCT / meta-analysis	Low periconceptional folate causes fetal neural tube defects (spina bifida, anencephaly) and raises preterm birth, growth restriction and miscarriage risk.	NIH ODS / USPSTF – Folate (opens in a new tab)
Reproductive & Developmental	Eat enough of	Strong	RCT / meta-analysis	Low periconceptional folate causes fetal neural tube defects (spina bifida, anencephaly) and raises preterm birth, growth restriction and miscarriage risk.	Effect of folate intake on health outcomes in pregnancy: a systematic review and meta-analysis, Nutr J 2012 (opens in a new tab)
Cardiovascular	Eat enough of	Moderate	Cohort / observational	Deficiency raises homocysteine, contributing to vascular endothelial dysfunction and cardiovascular/stroke risk.	StatPearls – Folate (opens in a new tab)

Linked to getting too much

Where an excess of Folate (B9) is linked: 1 source.In the order the Map holds them: strongest evidence first. That is a statement about the evidence, not about what matters most.
Condition or system	Direction	Strength	Evidence type	What was found	Source
Brain fog & memory	Don't overdo	Moderate	Cohort / observational	People with low B12 plus high folate have lower cognitive test scores and higher homocysteine/MMA; excess folic acid may exacerbate B12-related cognitive decline.	Folic-acid–B12 masking review (opens in a new tab)

The Healthspan Map is part of Fix the Floor, a book by Aamir Malik. About the book