Vitamin D Deficiency in Infants Affects Mental Health? A Must-Read for Pregnant Women: Vitamin D Could Potentially Prevent 15% of Schizophrenia Cases — Latest Danish Research

Prologue: The Future of the "Mind" Illuminated by the Vitamin of Light
The Nordic countries, where half the year is cloaked in a long winter. A monumental epidemiological study, tracking the mental trajectory of children born under pale sunlight for over 35 years, is now shaking the world. A joint analysis by the Danish National Serum Institute and the University of Queensland, published in May 2025, reported that a deficiency in blood 25-hydroxyvitamin D during the neonatal period significantly increases the risk of developing mental disorders during adolescence to young adulthood.

Chapter 1: What 71,793 Dried Blood Spots Revealed

The research team analyzed "dry spots" of umbilical cord blood preserved from 71,793 individuals born between 1981 and 2005, classifying 25(OH)D concentrations into quintiles. Children born in the lowest quintile (<12.5 nmol/L) had a higher risk compared to those in the median quintile (32.2–39.9 nmol/L).

• Schizophrenia Risk: 1.44 times

• Autism Spectrum Disorder: 1.26 times

• ADHD: 1.21 times

If we could simply supplement vitamin D for newborns deficient worldwide, 15% of schizophrenia and 9% of ADHD cases could be avoided, researchers estimate.

Chapter 2: Three Mechanisms by Which Vitamin D Affects Brain Wiring

1. Neuroimmune Model — Vitamin D receptors are abundant in microglia, suppressing the runaway of inflammatory cytokines.

2. Synapse Formation Model — Controls axon elongation in the hippocampus and frontal lobe, optimizing plasticity.

3. Epigenetic Model — Adjusts transcription of neurodevelopmental genes through DNA methylation.

Animal experiments have also reported that deficiency in the late pregnancy period shortened dendrites in the hippocampal CA1. Such multifaceted effects are being discussed as potentially leaving long-term impacts on the brain during sensitive periods.

Chapter 3: The Reality of "Hidden Vitamin D Deficiency" in the World and Japan

Not limited to the Nordic countries, regions north of latitude 35 degrees with little sunlight in winter, or cultural areas with thorough UV protection even in sunny regions, have high deficiency rates among pregnant women and infants. In the 2024 multi-center survey by the Japan Society of Obstetrics and Gynecology,

• 80.2% of winter pregnant women were below 30 ng/mL (latent deficiency)

• 30.5% were below 20 ng/mL (clear deficiency)

. The current situation, where awareness has not progressed as much as for folic acid or iron, is highlighted.

Chapter 4: The "Real Voices" Reflected on Social Media

• X (formerly Twitter): Psychiatrist Icchi posted, "Vitamin D is inexpensive and has few side effects. If even one disease can be prevented with supplementation, there's no reason not to do it," receiving 32,000 likes.

• Reddit /r/science: The most supported comment questioned the methodology, asking, "Can confounding factors like poverty and diet be excluded?"

• Domestic Mom Forum: Many practical concerns, such as "Considering supplements for winter-born children" and "How to balance sunscreen and sunbathing?"
  
  
  

Chapter 5: Expert Opinions — Are Supplements a Savior or a Magic Bullet?

Research Leader Professor John McGrath

"Randomized controlled trials are needed to prove causality, but the biological plausibility is high. At the very least, pregnant women's blood 25(OH)D should aim for30 ng/mL or more."

Pediatric Endocrinologist Dr. Tim Jones

"We must not forget the risk of hypercalcemia due to overdose."

The Japanese Society for Pediatric Endocrinology is presenting the following recommendations in its 2025 revised guidelines:

• From a few days after birth to 12 months: 400 IU/day

• Preterm infants: 600 IU/day

as a proposed guideline.

Chapter 6: Implications for Public Health Policy

• United Kingdom: Legislation to fortify infant formula and cereals with vitamin D.

• New Zealand: Providing free government-funded supplements to pregnant women.

• Japan: A Ministry of Health research team proposes adding a vitamin D section to maternal and child health handbooks and introducing blood level measurements in regular check-ups.

The social cost of supplements is estimated at approximately 1,200 yen per person per year, and the potential reduction in mental illness medical expenses could be several dozen times that amount.

Chapter 7: Five Measures Individuals Can Take

Epilogue: How to Nurture the Light for the Future

Vitamin D is also called the "sunshine vitamin," but its deficiency is a "modern disease" born from social structures and lifestyles. This massive cohort study merely suggested a correlation—however, if a supplement in hand and a few minutes of outdoor play can protect a child's mental health, it is indeed an investment in the future. The simplest preventive measure we can take might be to bask in the sunlight with our babies.