Seasonal depression in Belgium: sugar, serotonin, BDNF, and ginger (2025)

Belgium, a Hotbed for SAD

• Latitude 50°N (Brussels) → minimal winter sun (Dec-Jan: 1–2h effective/day)
• Predominantly cloudy skies (200+ cloudy days/year)
• 5–10% clinical SAD prevalence, 20–30% sub-syndromic ("winter blues")
• Belgian winter food culture → fries, beer, chocolate → sugar + alcohol → exacerbated SAD

Molecular Mechanisms: SAD and Sugar

1. Melatonin and Circadian Phase Shift

• Light ↓ (Belgian winter) → SCN (suprachiasmatic nucleus) → prolonged melatonin
• Melatonin ↑↑ → daytime sleepiness, lethargy, hypersomnia
• Sugar → NF-κB → BMAL1 ↓ → poorly regulated melatonin (delayed phase)
• AGE (glycation) → BMAL1 degradation → circadian clock even more desynchronized

2. Serotonin and Light

• Light → TPH2 activation → 5-HT ↑ → mood, energy, motivation
• Belgian winter → TPH2 under-activated → 5-HT ↓ → depressive mood
• Sugar → dysbiosis → tryptophan competition (IDO) → kynurenine ↑ instead of 5-HT
• IDO activated by NF-κB → kynurenine ↑ → NMDA-R → neuro-excitotoxicity → depression
• GIMBER (35g sugar) → IDO ↑ → 5-HT ↓ → SAD exacerbated in winter

3. BDNF and Winter Hippocampus

• SAD → hippocampal BDNF ↓ (MRI studies: hippocampal volume correlated with SAD severity)
• NF-κB → IL-6 → SOCS3 → TrkB signaling ↓ → BDNF plasticity ↓
• Sugar → NF-κB → BDNF ↓ → exacerbated seasonal depression
• Ginger → NF-κB ↓ → BDNF TrkB supported → hippocampus protected

4. Vitamin D and Ginger: Winter Synergy

• Belgian winter → vitamin D ↓ (no UVB) → VDR ↓ → less regulated NF-κB
• Vitamin D deficiency → TPH2 ↓ → 5-HT ↓ (VDR regulates TPH2)
• Ginger → Nrf2 → NF-κB ↓ → partial compensation for VDR/NF-κB deficiency
• INTI + vitamin D3 (1000–2000 IU/day) = optimal winter synergy against SAD

INTI Winter SAD Protocol