Explore Dr. Retzler’s HormoneSynergy® Longevity Medicine Resource Library
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Longevity Medicine, Functional Wellness & Anti-Aging Insights from HormoneSynergy®

Welcome to the HormoneSynergy® Longevity Medicine Blog, a physician-guided clinical library led by Dr. Kathryn Retzler. Our articles cover the systems that most often shape health with age: metabolic health, hormones, cardiovascular and kidney risk, body composition, bone and muscle, brain health, sleep, gut health, nutrition, supplements, and the biology of aging.

The library is organized around clinical questions rather than trends. Some articles review new research. Others explain testing, treatment, nutrition, or a condition patients commonly encounter. Across the collection, the standard is the same: evidence first, appropriate uncertainty, and enough clinical context to separate useful medicine from wellness marketing.

Start with the HormoneSynergy® Longevity Medicine Framework

New & recently updated:

Metabolic Health & Insulin Resistance

Clinical resources on insulin resistance, glucose regulation, metabolic syndrome, visceral fat, prediabetes, obesity and GLP-1-based care within a broader longevity medicine plan.

Kidney Health & Cardiovascular-Kidney-Metabolic Health

Kidney health belongs in the same clinical conversation as blood pressure, diabetes, insulin resistance, obesity and cardiovascular risk. These resources cover early detection, CKD, albuminuria, nutrition and CKM health.

Body Composition, Bone & Muscle Longevity

Resources on DEXA, SECA, visceral fat, lean mass, sarcopenia, bone density, exercise and preservation of physical reserve with age.

Gut Health, Microbiome & Immune Signaling

Clinical education on the microbiome, intestinal barrier, fiber, inflammation, gut-brain signaling, immune biology and the growing connections between gut, metabolic and kidney health.

Food Quality, Vitamins, Supplements & Wellness Claims

Evidence-based guidance on nutrient gaps, supplement quality, interactions, food claims and longevity products, with an emphasis on where supplementation helps and where marketing outruns the evidence.

  • When Knowing Isn’t Enough: Making Health Changes That Last

    by Daniel Soule
    Woman walking on a leafy Pacific Northwest path beside the title “When Knowing Isn’t Enough: Making Health Changes That Last.”

    Knowing what supports health is a beginning. Putting that knowledge into practice takes a plan that accounts for habits, stress, readiness, and the demands of everyday life.

  • Nicotinamide Riboside and Brain Health: What a Major Randomized Trial Tells Us About NAD⁺ and Neuroprotection

    by Daniel Soule
    HormoneSynergy® editorial image illustrating nicotinamide riboside, NAD⁺ metabolism, mitochondrial function, and neurological research.

    A major randomized trial published in JAMA found that nicotinamide riboside did not slow early Parkinson's disease over 52 weeks. HormoneSynergy® examines the findings alongside research on NAD⁺ metabolism, mitochondrial function, mild cognitive impairment, and the appropriate clinical role of NR supplementation.

  • Intensive Blood Pressure Treatment: What 88,830 Patients Tell Us About Heart and Kidney Protection

    by Daniel Soule
    HormoneSynergy® editorial on a meta-analysis of intensive blood pressure treatment, cardiovascular event prevention, kidney filtration, and chronic kidney disease.

    A new JAMA Cardiology analysis of 88,830 participants found that more intensive blood pressure treatment reduced cardiovascular events in adults with and without chronic kidney disease. HormoneSynergy® examines the benefits, changes in eGFR, kidney failure outcomes, and implications for preventive cardiovascular and kidney care.

  • Are Men's Testosterone Levels Declining? What the Research Reveals About Hormones, Fertility, and Longevity

    by Daniel Soule
    Men representing different generations in a HormoneSynergy clinical editorial image about testosterone decline, male reproductive health, metabolism, and longevity.

    Testosterone levels appear to have declined across generations of men, while sperm counts have also fallen substantially. HormoneSynergy® examines the research behind these trends, the possible contributions of visceral fat and environmental exposures, and what they mean for healthy aging.

  • Alzheimer's Research Is Moving Toward Earlier Intervention: Can Prevention Begin Before Memory Changes?

    by Daniel Soule
    HormoneSynergy® editorial image illustrating Alzheimer's prevention research, brain vascular health, genetic susceptibility, and earlier clinical intervention.

    Alzheimer's research is moving earlier in the disease process, with prevention trials investigating people who have no cognitive symptoms but may have elevated biological or genetic risk. HormoneSynergy® examines the October 2026 clinical-trials update, APOE4, emerging blood biomarkers, metabolic and vascular health, and what preventive longevity medicine can reasonably address today.

  • Pendulum™ Gut Fuel: Feeding the Microbiome Through Resistant Starch, Prebiotic Fiber, and Polyphenols

    by Daniel Soule
    Fiber-rich breakfast featuring oats, berries, seeds, and prebiotic nutrition illustrating Pendulum Gut Fuel, resistant starch, Akkermansia, and microbiome support for healthy aging.

    A healthy gut microbiome depends on more than introducing beneficial bacteria. It also requires the right nutritional environment. Pendulum™ Gut Fuel combines resistant potato starch, acacia fiber, baobab, oat bran, and grape seed polyphenols to support microbial activity, digestive regularity, and the metabolic pathways connecting the gut with whole-body health. HormoneSynergy® examines the formulation, the clinical research, and its potential place in a preventive longevity medicine strategy.

  • The Heart–Kidney–Metabolic Connection: A More Complete Approach to Preventive Medicine

    by Daniel Soule
    HormoneSynergy® preventive longevity medicine editorial showing the interconnected roles of cardiovascular, kidney, and metabolic health.

    Heart disease, kidney dysfunction, and metabolic disease often develop together, long before symptoms appear. HormoneSynergy® examines how ApoB, insulin resistance, visceral fat, kidney testing, and vascular imaging contribute to a more complete understanding of cardiovascular–kidney–metabolic risk.

  • Urolithin A: Mitochondrial Health, Brain Blood Flow, and What Human Trials Actually Show

    by Daniel Soule
    HormoneSynergy® editorial illustration of mitochondrial function and cerebral vascular responses in emerging urolithin A research.

    A new October 2026 randomized trial found that urolithin A altered brain blood-flow responses during cognitive testing without significantly improving peripheral endothelial function or cognitive performance. HormoneSynergy® examines the findings alongside previous human studies of mitochondrial health, muscle function, and aging.

  • GLP-1 Medications and Biological Aging: Are We Looking Beyond Weight Loss?

    by Daniel Soule
    HormoneSynergy editorial image illustrating research into GLP-1 medications, cellular aging, metabolic health, and longevity in older adults.

    New research published in Nature suggests that semaglutide may influence biological aging beyond its effects on weight and glucose. Dr. Kathryn Retzler examines the animal findings, the human cardiovascular and metabolic evidence, and what GLP-1 medications may eventually contribute to preventive longevity medicine.

  • Which Diet Is Right for You? Beyond the Diet Wars

    by Daniel Soule
    Adults sharing a protein-conscious Mediterranean meal with vegetables, fish, legumes, olive oil, and whole grains, illustrating nutrition for healthy aging.

    Mediterranean, ketogenic, vegan, carnivore, and other diets each have devoted advocates. The evidence for long-term health, however, is not equally strong across them. We examine why HormoneSynergy® favors plant-forward Mediterranean nutrition with adequate protein, and when individual health needs justify a different approach.

  • Aria's Philosophy of Being: Who Would You Be If You Didn't Know Who You Were?

    by Daniel Soule
    Aria, a black Shepadoodle with a white beard, rests on her doghouse beneath the stars, contemplating identity, aging, and the philosophy of simply being.

    After overhearing Daniel listening to Alan Watts and reflecting on identity, attachment, and aging, Aria begins considering a question humans rarely ask themselves: who would we be without everything we've been taught to believe about who we are?

  • Forget “Ferritin Face”: The Important Story Is That the Definition of Iron Deficiency Just Changed

    by Daniel Soule
    Physician reviewing ferritin and iron laboratory results with a patient at HormoneSynergy® in Lake Oswego, Oregon, illustrating the 2026 ASH iron deficiency guidelines.

    “Ferritin Face” may be trending on social media, but your appearance cannot diagnose iron deficiency. The more important development is new 2026 guidance from the American Society of Hematology that raises the ferritin threshold used to identify iron deficiency in adults. Here is what changed, why ferritin can be low even without anemia, and why interpreting iron studies requires more than looking at a laboratory reference range.