Do low DHEA-S, low free testosterone, and high SHBG indicate reduced anabolic bioavailability in older men?

In men over 60, endocrine senescence is characterized by declining adrenal and testicular activity alongside rising transport protein levels, which collectively limit circulating hormone availability.

Endocrine mechanisms and bioavailability

• Transport and active fractions: Age-related elevations in sex hormone-binding globulin (SHBG) bind circulating testosterone with high affinity. This reduces the free, biologically active fraction that is capable of interacting with target tissue receptors, directly correlating with declines in lean mass and muscle strength.
• Adrenal precursor depletion: A decline in dehydroepiandrosterone sulfate (DHEA-S) reflects adrenal senescence, reducing the systemic reservoir of weak androgen precursors. This limits local intracrine conversion into potent active androgens within peripheral target tissues.

Tissue-specific signaling cascades

• Skeletal muscle blunting: Reduced androgen bioavailability downregulates crucial growth-related translation pathways in skeletal muscle, specifically inhibiting the mTOR pathway, insulin-like growth factor 1 receptor (IGF-1R), and myogenin, which delays muscle protein synthesis.
• Bone suppression pathways: In bone tissue, a loss of androgen-mediated suppression in osteocytes leads to elevated sclerostin (SOST) levels. High sclerostin binds to LRP5/6 receptors, blocking the canonical Wnt/β-catenin signaling pathway (WNT10b–β-catenin–RUNX2), which suppresses osteoblastogenesis and bone matrix formation.
• Immune and repair dynamics: Decreased DHEA-S compromises immune-supportive signaling by reducing thymic output and impairing cutaneous wound-healing pathways.

Bottom line

• The co-occurrence of high SHBG, low free testosterone, and low DHEA-S indicates significantly reduced anabolic bioavailability. This state limits tissue regeneration in older men by suppressing muscular mTOR/IGF-1 pathways, accelerating bone loss via sclerostin-mediated Wnt inhibition, and impairing immune-repair signaling.