Can aging, phthalates, SHBG, visceral fat, and low DHEAS/IGF-1 lower androgen signaling in older men?

In aging men, tissue-available androgen signaling is governed by a complex web of testicular decline, metabolic shifts, environmental exposures, and secondary hormonal alterations.

Cellular and endocrine disruption

• Leydig cell senescence: Normal aging naturally diminishes Leydig cell quantity and steroidogenic capacity, directly reducing total testosterone synthesis.
• Toxicant exposure: High-molecular-weight phthalates act as anti-androgens, promoting Leydig cell mitochondrial damage and cellular senescence (via upregulated p21/p16 pathways). This directly compromises testosterone output.

Transport and metabolic sequestration

• SHBG binding: Elevated sex hormone-binding globulin (SHBG) binds circulating testosterone with high affinity, preventing its diffusion into target tissues and decreasing biologically active free androgens.
• Visceral adiposity: In a bidirectional metabolic loop, visceral fat accumulation and insulin resistance suppress hepatic SHBG and impair hypothalamic-pituitary-gonadal (HPG) axis responsiveness. Phthalate exposure exacerbates this pathway by independently promoting visceral obesity and insulin resistance.

Growth factor and precursor depletion

• Synergistic signaling: Central adiposity and insulin resistance suppress growth hormone responsiveness, which accelerates the age-related decline of both the adrenal androgen precursor dehydroepiandrosterone sulfate (DHEAS) and insulin-like growth factor 1 (IGF-1). The loss of these co-factors limits raw precursors and growth signals that optimize tissue-level androgen receptor expression.

Bottom line

• The convergence of age-related Leydig cell decay, phthalate exposure, elevated SHBG, visceral obesity-insulin resistance, and diminished DHEAS and IGF-1 synergistically restricts systemic and tissue-level androgen availability in older men.