Slippery elm is the powdered inner bark of a North American tree that swells into a thick gel, sold to soothe an irritated throat or gut. The gel coats the surfaces it touches and nothing crosses the gut wall. Throat relief is the best-supported use; digestive findings are weak. Cheap, well tolerated, and not a longevity intervention. Its cost: it blunts the absorption of anything swallowed with it. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Ferritin | 50–150 ng/mL (men), 50–100 ng/mL (women) | Detects iron depletion from tannin and fiber binding |
| hs-CRP | Below 1.0 mg/L | Confirms no systemic inflammation is being masked or missed |
| Fecal calprotectin | Below 50 µg/g | Distinguishes functional symptoms, which may respond, from true bowel inflammation, which will not |
| TSH | 0.5–2.0 mIU/L | Earliest signal that levothyroxine absorption has been reduced by the gel |
| Serum 25-hydroxyvitamin D | 40–60 ng/mL | Tracks fat-soluble vitamin uptake, which viscous fiber can blunt |
| Urinary lactulose-to-mannitol ratio | No established target range; the change from the individual's own baseline is tracked instead | Measures gut-barrier leakiness, the one mechanistic endpoint reported for a slippery elm formula |
Cadence: Symptoms reassessed at four weeks; the level or control marker of any narrow-margin medicine rechecked at six to eight weeks; ferritin and inflammatory markers repeated at three months, then every six to twelve months if use continues