Saw palmetto — The Natural 5α-Reductase Inhibitor
Saw palmetto is a botanical extract rich in fatty acids and phytosterols, widely used for its antiandrogenic and anti-inflammatory properties. While primarily studied for prostate health and hair loss via 5α-reductase inhibition, its relevance to longevity lies in its potential to modulate androgen signalling and reduce systemic inflammation, though robust clinical efficacy remains unproven.
Mechanism of Action
The lipid fraction of saw palmetto (Serenoa repens) extract contains free fatty acids and phytosterols that act as non-competitive inhibitors of 5α-reductase types 1 and 2. This inhibition reduces the conversion of testosterone to dihydrotestosterone (DHT), a potent androgen implicated in prostate enlargement and androgenic alopecia. Additionally, saw palmetto exhibits anti-inflammatory properties by inhibiting cyclooxygenase (COX) and lipoxygenase (LOX) pathways, thereby reducing the production of inflammatory prostaglandins and leukotrienes. It may also competitively bind to androgen receptors, further attenuating DHT-mediated cellular signalling.
Human Trial Evidence
Saw palmetto has been extensively studied in humans for benign prostatic hyperplasia (BPH) and lower urinary tract symptoms (LUTS). Large-scale, high-quality randomised controlled trials, including the STEP (2006) and CAMUS (2011) trials published in NEJM and JAMA, have consistently shown that saw palmetto extract is no more effective than placebo for LUTS or BPH. There are no published human longevity trials.
Dosing Protocol
320 mg/day is the standard clinical dose, typically taken as a lipidosterolic extract (e.g., Permixon). In clinical trials such as the CAMUS study, doses were escalated up to 960 mg/day (triple dose) without additional benefit for lower urinary tract symptoms. It is generally taken with food to minimise gastrointestinal discomfort.
Safety & Contraindications
Saw palmetto is generally well tolerated, with a safety profile comparable to placebo in large clinical trials even at triple the standard dose. Mild adverse effects include gastrointestinal discomfort, headache, and fatigue. It should be used with caution in individuals taking antiplatelet or anticoagulant medications due to potential theoretical interactions, and is contraindicated in pregnant or breastfeeding women due to its antiandrogenic effects.