Metformin vs Spermidine

Mechanism

Metformin activates AMP-activated protein kinase (AMPK) via inhibition of mitochondrial Complex I, increasing the AMP/ATP ratio. AMPK activation triggers a cascade of metabolic effects: inhibition of hepatic gluconeogenesis, enhanced glucose uptake in skeletal muscle via GLUT4 translocation, and suppression of mTORC1 signaling. In the longevity context, metformin's mTOR inhibition mimics caloric restriction signaling, activating autophagy, reducing inflammatory cytokines (IL-6, TNF-a), decreasing insulin and IGF-1 signaling, and modulating the gut microbiome (increasing Akkermansia muciniphila). It also reduces AGE formation and mitochondrial ROS production.

Standard Dosing

Research indicates 500-1000 mg daily for longevity/anti-aging protocols. Standard diabetes dosing: 500-2550 mg daily.

Timing

Take with food (dinner) to minimize GI side effects. Extended-release formulation once daily with dinner. Immediate-release split into 2-3 doses with meals.

Cycle Duration

Ongoing for longevity applications. The TAME (Targeting Aging with Metformin) trial is designed to assess long-term geroprotective effects.

Side Effects

• GI distress: nausea, diarrhea, bloating, metallic taste (common initially, improves with XR formulation)
• Vitamin B12 deficiency (with chronic use — monitor annually)
• Lactic acidosis (rare but serious — primarily in renal impairment)
• Potential blunting of exercise-induced mitochondrial adaptations (debated)
• Weight loss (often considered a benefit)

Contraindications

• eGFR <30 mL/min/1.73m2 (contraindicated) or <45 (use with caution)
• Acute or chronic metabolic acidosis including lactic acidosis
• Heavy alcohol consumption
• Acute decompensated heart failure
• Hepatic failure
• Planned procedures with iodinated contrast dye

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Mechanism

Spermidine is an endogenous polyamine that induces autophagy primarily through inhibition of the acetyltransferase EP300 (p300), leading to hypoacetylation of multiple autophagy-related proteins and subsequent activation of the core autophagy machinery (Atg5, Atg7, Beclin-1). It promotes mitophagy (selective clearance of damaged mitochondria) and is essential for the hypusination of eukaryotic translation initiation factor 5A (eIF5A), a post-translational modification critical for TFEB-mediated lysosomal biogenesis. Spermidine also reduces age-related inflammation by suppressing NF-kB signaling and promotes cardiovascular health through improved endothelial nitric oxide bioavailability.

Standard Dosing

Research indicates 1-6 mg/day orally for longevity and autophagy support. Epidemiological data associates >80 micromol/day dietary spermidine intake with reduced cardiovascular mortality.

Timing

Morning with or without food. Some protocols suggest taking before a fasting period to potentiate autophagy (fasting naturally increases endogenous spermidine synthesis).

Cycle Duration

Ongoing. Endogenous spermidine levels decline with aging, suggesting lifelong supplementation may be beneficial.

Side Effects

• Generally very well-tolerated
• Mild GI discomfort at higher doses
• Headache (rare)

Contraindications

• Known hypersensitivity to polyamines
• Pregnancy and breastfeeding (insufficient safety data at supplemental doses)
• Active malignancy (polyamines promote cell proliferation in rapidly dividing cells — debated)
• Wheat allergy (if from wheat germ source)

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