D-serine is an amino acid the brain uses for learning and memory, and its natural supply falls with age. Restoring it reverses memory decline in aged animals, but human evidence is thin and mixed. A kidney-safety concern seen in rats has rarely appeared in people, leaving it a promising but unproven option for brain aging. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Estimated glomerular filtration rate (eGFR) | ≥90 mL/min/1.73m² | Gates eligibility; detects any decline in kidney filtering |
| Serum creatinine | ≈0.6–1.0 mg/dL | Core marker of filtering capacity feeding the eGFR estimate |
| Cystatin C | Within reference range | Confirms filtering independent of muscle mass |
| Urinalysis (protein, granular casts) | Absent | Detects early kidney-tube injury before blood markers move |
| Blood urea nitrogen (BUN) | ≈7–18 mg/dL | Supporting marker of kidney clearance and hydration |
Cadence: Kidney labs and urinalysis at 1–2 weeks, again at 4–6 weeks, then every 3–6 months during continued use