Thymulin is a zinc-dependent thymus hormone that helps immune T-cells mature, and its activity falls sharply with age. Its best-supported use today is as a marker of zinc status and reversible immune aging. Benefits beyond that rest almost entirely on animal studies, and its safety in people is untested. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Serum/plasma zinc | ~90–110 mcg/dL | Enables thymulin activity; deficiency inactivates the hormone |
| Active/total thymulin ratio | Higher ratio = better activity | Direct readout of biologically active hormone and zinc bioavailability |
| Serum copper | ~90–120 mcg/dL | Guards against copper depletion from chronic zinc supplementation |
| hs-CRP | <1.0 mg/L | Tracks systemic inflammation that suppresses thymic function |
| IL-6 (interleukin-6) | Low-normal per assay | High IL-6 drives thymic involution and lowers zinc bioavailability |
| CBC with lymphocyte subsets | Age-appropriate normal; adequate T-cell counts | Reflects downstream immune capacity thymulin aims to support |
Cadence: Reassess zinc and inflammatory markers ~4–8 weeks after a change, then every 3–6 months; check copper every 6–12 months if zinc is supplemented chronically.