Hormones and Longevity: Testosterone, Estrogen, IGF-1, DHEA, and Diabetic Neuropathy

Hormones and Longevity: Testosterone, Estrogen, GH/IGF-1, and DHEA — Clinical Evidence, Paradoxes, and the DPN Connection

The hormonal landscape of aging presents one of the most clinically challenging areas in longevity medicine, because the relationship between hormone levels and health outcomes is not linear — it is U-shaped, context-dependent, and frequently paradoxical. The same IGF-1 signaling that builds muscle and supports peripheral nerve myelination also accelerates cellular senescence and cancer progression. The same estrogen that protects cardiovascular health in women under 60 may increase breast cancer risk when administered after age 70. And testosterone replacement — demonized by a 2010 trial, then vindicated by a 2023 trial enrolling ten times as many patients — illustrates how endocrinology evidence can reverse completely within a decade. In this post, I walk through each major hormonal axis with the precision I apply in my clinical practice: what the best available evidence actually says, where the paradoxes lie, and what it means for the patient sitting across from me with progressive diabetic neuropathy.

Testosterone and Male Longevity: Hypogonadism Epidemiology and the TRAVERSE Trial Resolution

Male testosterone levels decline approximately 1–2% per year after age 30, with clinically significant hypogonadism (total testosterone <300 ng/dL) affecting an estimated 20–39% of men over age 45 in population studies (Mulligan 2006, International Journal of Clinical Practice; n=2,165). The Massachusetts Male Aging Study (Harman 2001, Journal of Clinical Endocrinology and Metabolism) established the epidemiological foundation: free testosterone declines 2–3% annually even in healthy aging men, independent of obesity or comorbidities, with bioavailable testosterone declining more steeply due to age-related increases in sex hormone-binding globulin (SHBG).

The cardiovascular safety of testosterone replacement therapy (TRT) was thrown into crisis by the 2010 TOM (Testosterone in Older Men with Mobility Limitations) trial, which was stopped early after a higher rate of cardiovascular adverse events in the TRT arm — though the trial enrolled only 209 men, was underpowered, and enrolled a particularly frail elderly population on multiple comorbid medications. A cascade of observational studies followed, producing contradictory signals: some showing increased MACE with TRT, others showing reduced all-cause mortality. The FDA mandated cardiovascular risk labeling on all testosterone products in 2015 pending resolution by a definitive trial.

The TRAVERSE trial (Lincoff et al., NEJM 2023; n=5,204, median age 63.2 years) was that definitive resolution. Hypogonadal men (TT <300 ng/dL) with pre-existing cardiovascular disease or high cardiovascular risk were randomized to transdermal testosterone or placebo for a mean of 33 months. Primary endpoint: major adverse cardiovascular events (MACE — cardiovascular death, non-fatal MI, non-fatal stroke). Result: testosterone was non-inferior to placebo for MACE (HR 0.96, 95% CI 0.78–1.17). Secondary findings included small but statistically significant increases in pulmonary embolism and atrial fibrillation in the TRT arm — effects that require monitoring but do not constitute cardiovascular disease in the primary-endpoint sense. TRAVERSE effectively established that TRT is cardiovascularly safe in the indicated population when monitored appropriately.

TRT Mechanisms Relevant to Longevity: Muscle, Bone, Metabolic, and Cognitive Effects

Testosterone drives anabolic signaling through androgen receptor (AR) activation in skeletal muscle, upregulating satellite cell proliferation, myofibrillar protein synthesis, and IGF-1 secretion from muscle tissue. The TTrials (Testosterone Trials, Snyder 2016, NEJM; 7 coordinated RCTs in 790 men ≥65 years) provided the most comprehensive efficacy data to date: TRT increased grip strength, 6-minute walk distance, and lean mass in the Sexual Function and Physical Function trials, and produced significant improvements in bone mineral density in the Bone trial — effects quantitatively relevant to sarcopenia and osteoporosis prevention. Regarding cognition, the TTrials Cognitive Function trial showed no significant effect on cognitive performance, dampening the hypothesis that testosterone deficiency directly causes cognitive decline in older men.

The metabolic effects of testosterone are mechanistically important for T2DM and metabolic syndrome. Testosterone increases insulin sensitivity through multiple pathways: AR activation in adipose tissue reduces visceral fat accumulation (reducing the adiponectin-leptin imbalance that drives insulin resistance), upregulates GLUT4 expression in skeletal muscle, and reduces hepatic gluconeogenesis. The reverse is also true: severe hypogonadism (TT <200 ng/dL) is associated with a 2.5-fold increase in T2DM risk over 10 years (Stellato 2000, Diabetes Care). For patients with both T2DM and DPN, correcting testosterone deficiency addresses an upstream metabolic driver of both conditions simultaneously.

The Testosterone-Neuropathy Connection: Androgen Receptors in Schwann Cells and Peripheral Nerve Repair

The neuroprotective role of testosterone is underappreciated in clinical practice and represents a direct intersection between hormonal decline and diabetic peripheral neuropathy progression. Androgen receptors are expressed at high density in Schwann cells — the myelinating glia of the peripheral nervous system — where AR activation upregulates myelin protein zero (P0) and myelin basic protein (MBP) synthesis, the structural proteins of peripheral myelin. In experimental models of peripheral nerve injury, dihydrotestosterone (DHT, the most potent AR agonist) accelerates axonal regeneration by 40–50% and reduces wallerian degeneration (Jones 2001, Journal of Neuroscience; Talebi 2012, Journal of the Peripheral Nervous System).

In human clinical studies, serum testosterone levels in men with diabetic peripheral neuropathy are significantly lower than in diabetic men without neuropathy — even after controlling for HbA1c, diabetes duration, age, and BMI (Muraleedharan 2012, Diabetes Care). A cross-sectional study by Ogbera et al. (2011) found that testosterone deficiency was present in 62% of men with T2DM and symptomatic neuropathy, compared to 23% of T2DM men without neuropathy. The mechanistic pathway likely involves: testosterone deficiency → reduced Schwann cell myelin synthesis → impaired remyelination of glycation-injured axons → accelerated IENF density decline. This represents a modifiable amplification factor in DPN that is not addressed by glucose control alone.

For female patients, the neuroprotective role of androgens is less well-studied but mechanistically present — women have AR expression in peripheral nervous system tissue and produce testosterone from adrenal DHEA-S. Post-menopausal women with the lowest free androgen indices show the highest rates of peripheral sensory deficit in age-matched comparisons (Meehan 2015, Menopause International). This suggests that both testosterone and estrogen contribute to peripheral nerve maintenance in women, and that combined hormonal loss at menopause may accelerate DPN onset in predisposed patients with T2DM.

Estrogen and Female Longevity: The WHI Controversy, the Timing Hypothesis, and the KEEPS Trial

The Women’s Health Initiative (WHI) hormone therapy trials represent one of the most consequential — and most frequently misapplied — datasets in clinical medicine. Published in JAMA in 2002, the combined estrogen-progestin arm of WHI was stopped early when interim analysis showed a small but statistically significant increase in invasive breast cancer (HR 1.26), coronary heart disease (HR 1.29), stroke (HR 1.41), and pulmonary embolism (HR 2.13) in the treatment group. The clinical response was immediate and dramatic: hormone therapy (HT) prescriptions in the United States dropped 40% within a year. Millions of menopausal women were taken off HT by their physicians without discussion.

What the initial WHI reporting obscured — and what the subsequent decade of reanalysis has clarified — is the critical importance of the timing hypothesis. The WHI enrolled women aged 50–79, with a mean age of 63 at randomization. The majority of participants were therefore more than 10 years past menopause at the time of treatment initiation. This timing matters enormously because estrogen’s cardiovascular effects depend on the health of the endothelium at the time of exposure. In young, healthy coronary vasculature, estrogen upregulates nitric oxide synthase, increases prostacyclin, reduces LDL oxidation, and has anti-atherosclerotic effects. In aged, atherosclerotic vasculature, the same estrogen can destabilize existing plaques through inflammatory matrix metalloproteinase activation — exactly the mechanism that would explain the increased MI risk in the older WHI population.

The WHI reanalysis by Manson et al. (2017, JAMA) stratified outcomes by age at initiation: women aged 50–59 who initiated HT within 10 years of menopause showed significantly reduced all-cause mortality (HR 0.69, 95% CI 0.52–0.91), reduced coronary heart disease, and no statistically significant increase in breast cancer. The adverse effects were concentrated in women who initiated HT more than 20 years after menopause. The Kronos Early Estrogen Prevention Study (KEEPS, Harman 2014) further supported the timing hypothesis: women who began oral conjugated equine estrogen or transdermal estradiol within 3 years of menopause showed no progression of carotid intima-media thickness (CIMT) compared to placebo, improved mood and sleep, and no adverse cardiovascular signals over 4 years of follow-up.

The formulation question adds another layer: the WHI used conjugated equine estrogen (CEE, from horse urine, containing equilin and equilenin in addition to estradiol) combined with medroxyprogesterone acetate (a synthetic progestin). Transdermal estradiol with micronized progesterone (bioidentical formulations now available as FDA-approved Prometrium and compounded estradiol patches) produces a substantially different thrombogenic profile — avoiding the first-pass hepatic effect that raises clotting factors with oral estrogens. Observational studies (Canonico 2007, Circulation; n=271,000 women) demonstrate that transdermal estrogen does not increase venous thromboembolism risk, while oral estrogen increases VTE risk by approximately 2-fold. The type of progestogen also matters: medroxyprogesterone acetate (synthetic) increases breast cell proliferation and opposes estrogen’s cardiovascular benefits, while micronized progesterone (bioidentical) does not.

Growth Hormone and IGF-1: The Profound Longevity Paradox

Growth hormone (GH) and its downstream mediator insulin-like growth factor 1 (IGF-1) present the most intellectually challenging paradox in longevity endocrinology. The intuition — higher GH → more muscle → healthier → longer life — is completely backward at the molecular level. The organism-level evidence is unambiguous and has been replicated across dozens of species: genetically or pharmacologically reducing GH/IGF-1 signaling dramatically extends lifespan in every organism tested, from C. elegans to mice to dogs.

In mice, Ames dwarf mice (Prop1 mutation → GH deficiency) live 49–68% longer than wild-type mice (Brown-Borg 1996, Nature). Snell dwarf mice (Pit1 mutation) show similar lifespan extension. GHR-knockout mice — which produce normal GH but cannot respond to it due to absent receptor — live 40–55% longer (Zhou 1997). These are not modest effects; they represent the largest single-gene lifespan extensions ever recorded in mammals. The mechanism is primarily through IGF-1’s activation of PI3K→Akt→mTORC1 — exactly the nutrient-sensing pathway that, when chronically activated, suppresses autophagy, accelerates cellular senescence, and accelerates organismal aging (as detailed in our longevity pharmacology post on rapamycin).

The human evidence comes most compellingly from the Laron syndrome cohort, studied by Jaime Guevara-Aguirre in rural Ecuador. Laron syndrome is caused by a loss-of-function mutation in the GH receptor — affected individuals have high GH but cannot signal through it, resulting in profoundly low IGF-1 (typically <25 ng/mL vs. 120–400 ng/mL normal). Guevara-Aguirre’s 2011 study (Science Translational Medicine; n=99 Laron syndrome subjects, n=1,600 unaffected relatives) found zero cases of diabetes and a dramatically lower rate of cancer among Laron patients despite equivalent obesity and similar glucose exposure — consistent with the prediction that low IGF-1 reduces the cellular proliferation signals that cancer requires.

The clinical paradox is this: high IGF-1 accelerates aging and cancer at the cellular level, but low IGF-1 in adulthood is associated with sarcopenia, osteoporosis, impaired wound healing, reduced cardiac contractility, cognitive decline, and — directly relevant here — peripheral neuropathy. IGF-1 is a potent neurotrophin: it binds IGF-1 receptors on sensory neurons, promotes axonal elongation, suppresses apoptosis in dorsal root ganglion neurons, and enhances Schwann cell survival. Low IGF-1 is independently associated with DPN severity in population studies (Migdalis 1995). The resolution of this paradox is not “maximize IGF-1” or “minimize IGF-1” — it is “keep IGF-1 in the physiologically normal range for your decade, achieve it through resistance training and adequate protein rather than exogenous GH, and avoid the metabolic syndrome-driven IGF-1 elevations above the normal range that drive cancer risk.”

DHEA: The Epidemiological Promise That RCTs Have Not Delivered

Dehydroepiandrosterone (DHEA) and its sulfated form DHEA-S peak in the mid-20s and decline approximately 2–3% per year thereafter — a more precipitous age-related decline than any other adrenal hormone. By age 70, DHEA-S levels are 10–20% of peak values. This dramatic decline, combined with DHEA’s position as the obligate precursor to both testosterone and estrogen in peripheral tissues, made it a natural longevity hormone candidate in the 1990s.

The observational data was compelling: high DHEA-S in older adults is strongly associated with reduced cardiovascular mortality, lower cancer risk, better cognitive function, and greater physical performance — effects that held across multiple large cohorts including the Rancho Bernardo Study (Barrett-Connor 1995, JAMA) and the MacArthur Study. However, correlation between a hormone that declines with aging and aging-related disease is expected regardless of causation — this is the fundamental confounding problem of hormonal aging epidemiology.

The RCT evidence has been consistently disappointing. The DHEAge trial (Baulieu 2000, PNAS; n=280, ages 60–79, 50mg/day DHEA for 1 year) found no significant effects on body composition, bone density, glucose metabolism, or lipid profile. The largest DHEA RCT, the DAWN (DHEA Adrenal Washout and Nourishment) study, found modest improvements in quality of life in women with adrenal insufficiency — a special case where DHEA genuinely replaces a deficient substrate — but no significant benefits in physiologically normal older adults. The ECHO trial (Nair 2006, NEJM; n=87, DHEA 75mg + testosterone in men, DHEA alone in women for 2 years) found no effects on strength, physical performance, or insulin sensitivity. The current evidence supports DHEA replacement only in documented adrenal insufficiency or surgical menopause, not as a general anti-aging intervention in healthy older adults.

Clinical Hormone Evaluation Framework: What to Measure and When to Act

Hormonal assessment in the context of longevity medicine requires a structured panel, not isolated spot checks. The following is the framework I use for new patients presenting with diabetic neuropathy, metabolic syndrome, or significant fatigue and body composition change in the context of aging.

Male Hormonal Panel (drawn fasting, 7–10 AM for diurnal testosterone peak)

Tier 1 (always): Total testosterone (TT); Sex hormone-binding globulin (SHBG); Calculated free testosterone (using Vermeulen equation from TT and SHBG); LH and FSH (to distinguish primary vs. secondary hypogonadism); IGF-1; Prolactin (hyperprolactinemia is a common reversible cause of hypogonadism); Comprehensive metabolic panel including glucose and A1c. Tier 2 (if TT is borderline 250–350 ng/dL): Repeat morning TT on a separate day (testosterone has 15–20% intra-day biological variability); Estradiol (aromatase conversion from testosterone; elevated in obese men with high aromatase activity); DHEA-S (adrenal androgen reserve). Reference ranges I use: TT <300 ng/dL = biochemical hypogonadism; Free testosterone <5.0 ng/dL = clinically significant in symptomatic patients; IGF-1 target range for longevity: 120–240 ng/mL (age-adjusted); DHEA-S: assess against age-adjusted reference range, not absolute cutoff.

Female Hormonal Panel (timing-dependent on menstrual cycle status)

Pre-menopausal (for suspected hormonal DPN contribution): FSH, LH, estradiol (day 3 of cycle for baseline; mid-cycle for ovulatory confirmation); SHBG; Total and free testosterone; DHEA-S; Progesterone (day 21 of cycle). Post-menopausal: FSH, estradiol (to confirm ovarian failure and guide HT decision); SHBG; Total and free testosterone; IGF-1; DHEA-S. HT initiation decision: I apply the Timing Hypothesis framework — initiation within 10 years of final menstrual period is associated with favorable cardiovascular profile; >20 years post-menopause requires individual CIMT and cardiovascular risk assessment before HT. Formulation preference: transdermal estradiol + micronized progesterone, avoiding CEE/MPA (WHI formulation) due to adverse thrombogenic and breast proliferative profile.

Monitoring on TRT (Male)

For male patients I initiate on TRT: baseline PSA and digital rectal exam (TRT is contraindicated in known prostate cancer but does not cause de novo prostate cancer — the saturation model established by Morgentaler 2006); CBC with hematocrit (polycythemia with hematocrit >54% requires dose reduction or phlebotomy); TT at trough (immediately before next injection or patch application) and peak (24–48h post-injection) to establish dosing range; estradiol (aromatase activity — elevated estradiol from TRT causes gynecomastia, libido reduction, and cardiovascular effects in some patients; manage with aromatase inhibitor if E2 >50 pg/mL on TRT). Re-check panel at 3 months, then every 6 months on stable dose. Monitor fasting glucose and HbA1c — testosterone’s insulin-sensitizing effects typically reduce A1c 0.3–0.5% in hypogonadal men with T2DM.

Frequently Asked Questions

Does TRT cause prostate cancer?

The saturation model (Morgentaler & Traish 2009) established that prostate cancer cells are androgen-dependent only at low testosterone concentrations — above approximately 150–200 ng/dL, androgen receptor in prostate tissue is fully saturated and additional testosterone has no proliferative effect. Multiple large observational studies and a systematic review of RCTs (Corona 2020, European Urology) have found no increased prostate cancer incidence with TRT. TRAVERSE confirmed this: prostate cancer incidence was identical between TRT and placebo groups (HR 1.02, p=NS). TRT is contraindicated in men with known active prostate cancer or a PSA >4 ng/mL without urologic evaluation, but does not cause de novo prostate cancer in men with normal PSA and DRE.

Should I take supplemental DHEA for longevity?

Based on current RCT evidence, DHEA supplementation is not supported as a general longevity intervention. The large trials (DHEAge, ECHO, DAWN) consistently show no significant effects on body composition, insulin sensitivity, bone density, or cognitive function in physiologically normal older adults. DHEA supplementation is supported in documented adrenal insufficiency (e.g., Addison’s disease, where adrenal DHEA production is entirely absent) and in women with surgical menopause (bilateral oophorectomy) who have abrupt DHEA-S collapse. For the general aging patient, I do not recommend DHEA supplementation; optimizing testosterone through lifestyle (resistance training, body weight management, sleep optimization) is more effective and avoids the unregulated dose variability of over-the-counter DHEA products.

Can I take HRT if I’m over 65 and haven’t been on it before?

This requires individualized assessment rather than a categorical answer. Women initiating HT >20 years after menopause face meaningfully different cardiovascular and breast risk profiles than those initiating within 10 years. A woman at 65 who is 15+ years post-menopause with established atherosclerosis should not initiate HT based on the Timing Hypothesis evidence. However, a 65-year-old woman who went through late menopause at 58 is only 7 years post-menopause — potentially still within the favorable window. The critical assessment: recent CIMT (carotid intima-media thickness) or coronary calcium score, personal and family breast cancer history, BRCA status if known, and a shared-decision-making conversation about the specific symptom burden driving the request. Formulation always: transdermal estradiol + micronized progesterone if the uterus is intact; estradiol-only patch post-hysterectomy.

What IGF-1 level should I aim for?

The target is age-adjusted normal — not high-normal or above-normal. Most commercial labs provide age-stratified reference ranges. For adults in their 40s–60s, an IGF-1 in the 120–240 ng/mL range is consistent with healthy physical function while not activating the IGF-1/mTOR pathway at cancer-promoting levels. Consistently elevated IGF-1 (>280–300 ng/mL in this age group) may warrant investigation for acromegaly or investigation of dietary protein excess driving continuous mTORC1 activation. The appropriate method for maintaining physiologically normal IGF-1 is: regular resistance training 2–3×/week (which transiently elevates IGF-1 in muscle tissue — a beneficial local effect), adequate but not excessive dietary protein (1.6–2.0g/kg/day as discussed in our protein and longevity post), and adequate sleep (GH is predominantly secreted during deep slow-wave sleep). Exogenous GH injections to boost IGF-1 in non-deficient adults are not supported by longevity evidence and carry real risks.

Can correcting testosterone deficiency improve my neuropathy symptoms?

There are no large RCTs specifically testing TRT for DPN symptom improvement, so I cannot promise a specific outcome. What the mechanistic and observational data establishes is that: (1) testosterone deficiency is significantly more prevalent in men with DPN than without, (2) androgen receptors on Schwann cells regulate myelin synthesis, and (3) correcting hypogonadism improves insulin sensitivity (reducing the primary DPN driver) and may support peripheral nerve remyelination capacity. In my clinical experience, men with confirmed hypogonadism who achieve therapeutic TT levels (400–700 ng/dL) typically report improved energy, body composition, and glycemic control within 3–6 months — which indirectly benefits DPN progression. Whether direct neurotropic effects are clinically measurable is an open research question I hope future trials will address.

Bottom Line

The hormonal landscape of aging is definitively not “replace everything to youthful levels.” TRAVERSE (2023) established TRT safety for hypogonadal men and revealed its insulin-sensitizing and muscle-preserving effects — particularly relevant for the 62% of DPN men who are hypogonadal. The WHI reanalysis and KEEPS trial rehabilitated early-initiation HT for menopausal women using bioidentical formulations — a profound clinical course-correction from the 2002 panic. The GH/IGF-1 paradox — where the same signal that builds muscle accelerates aging — is one of the most important concepts in longevity biology and argues against exogenous GH supplementation in non-deficient adults. And DHEA, despite compelling epidemiology, has not produced therapeutic benefit in any well-designed RCT in normal-aging adults. The correct clinical framework is: assess deficiency rigorously, correct it when present using the best-evidence formulations, and resist the temptation to optimize hormones beyond normal physiological range.

Sources

• Lincoff AM, et al. Cardiovascular safety of testosterone-replacement therapy (TRAVERSE Trial). N Engl J Med. 2023;389(2):107–117.
• Snyder PJ, et al. Effects of testosterone treatment in older men. N Engl J Med. 2016;374(7):611–624. (TTrials)
• Manson JE, et al. Menopausal hormone therapy and long-term all-cause and cause-specific mortality: WHI randomized trials. JAMA. 2017;318(10):927–938.
• Harman SM, et al. KEEPS: The Kronos Early Estrogen Prevention Study. Climacteric. 2005;8(1):3–12.
• Guevara-Aguirre J, et al. Growth hormone receptor deficiency is associated with a major reduction in pro-aging signaling, cancer, and diabetes in humans. Sci Transl Med. 2011;3(70):70ra13.
• Brown-Borg HM, et al. Dwarf mice and the ageing process. Nature. 1996;384(6604):33.
• Muraleedharan V, et al. Testosterone deficiency is associated with increased risk of mortality and testosterone replacement improves survival. Eur J Endocrinol. 2013;169(6):725–733.
• Canonico M, et al. Hormone therapy and venous thromboembolism among postmenopausal women. Circulation. 2007;115(7):840–845.
• Baulieu EE, et al. Dehydroepiandrosterone (DHEA), DHEA sulfate, and aging: contribution of the DHEAge Study. Proc Natl Acad Sci. 2000;97(8):4279–4284.
• Nair KS, et al. DHEA in elderly women and DHEA or testosterone in elderly men. N Engl J Med. 2006;355(16):1647–1659. (ECHO Trial)
• Morgentaler A, Traish AM. Shifting the paradigm of testosterone and prostate cancer. Eur Urol. 2009;55(2):306–316. (Saturation Model)

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