The endocrine system is one of the most intricate communication networks in the human body — a web of glands, receptors, and feedback loops that governs everything from energy metabolism and reproductive function to mood, cognition, and cardiovascular tone. Yet public discourse around it remains dominated by marketing language that is, at best, imprecise and, at worst, actively misleading.
This guide is not that. It is a structured, citation-backed examination of what the peer-reviewed literature actually says about hormonal health: which nutrients matter, which mechanisms are established, where evidence is genuinely limited, and what a thoughtful adult can reasonably do about it. I have written it for people who read abstracts, not headlines — who want to understand the endocrine system rather than be sold a solution to it.
The short answer, before we go deeper: the endocrine system responds to nutritional status, sleep quality, chronic stress load, and body composition in ways that are measurable and, to a meaningful degree, modifiable. Several micronutrients — zinc, magnesium, vitamin D, iodine, B vitamins — have documented roles in hormone synthesis or signalling. Certain adaptogens show credible evidence in controlled trials. The mechanisms are real. The marketing around them, however, routinely overstates the magnitude of effect.
What follows is the longer, more honest answer.
What "Hormonal Health" Actually Means
The phrase "hormonal health" has been so thoroughly colonised by supplement marketing that it is worth pausing to define it properly. The endocrine system comprises the hypothalamus, pituitary, thyroid, parathyroid, adrenal glands, pancreas, and gonads, among other tissues. These glands communicate via chemical messengers — hormones — that travel through the bloodstream and bind to specific receptors in target tissues. The system operates through feedback loops: rising levels of a hormone typically suppress the signals that triggered its release.
"Hormonal health," in any clinically meaningful sense, refers to the adequate synthesis, transport, receptor sensitivity, and clearance of these messengers. Problems can arise at any point in that chain. A person can produce adequate testosterone but have impaired receptor sensitivity. A person can have sufficient thyroid hormone in the blood but inadequate conversion of T4 to the active T3 form. These distinctions matter enormously, and they are almost never addressed in popular coverage.
What the evidence supports is this: nutritional deficiencies can impair hormone synthesis; chronic psychological stress can dysregulate the hypothalamic-pituitary-adrenal (HPA) axis; body composition influences oestrogen and testosterone metabolism; and the gut microbiome appears to play a role in thyroid function and oestrogen recycling. None of these findings translate cleanly into "take supplement X to fix your hormones." They do, however, point to specific, addressable mechanisms.
Testosterone: What the Evidence Actually Shows
Testosterone is the hormone most aggressively targeted by supplement marketing, and the gap between what products claim and what the literature supports is considerable. A 2024 systematic review examined all published data on so-called "testosterone boosters" and found that the evidence base for most commercially marketed products is either absent, methodologically weak, or derived from populations with pre-existing deficiency rather than healthy adults — Morgado 2024.
That said, deficiency states are real and worth addressing. A 2021 review of the causes of adverse testosterone changes in men identified a range of modifiable contributors: obesity, sleep disruption, chronic psychological stress, sedentary behaviour, and — critically — micronutrient deficiencies in zinc, vitamin D, and magnesium — Wrzosek 2021.
The zinc-testosterone relationship is one of the more consistently replicated findings in this space. Low serum zinc is associated with reduced serum testosterone in men with sexual dysfunction, though the association with erectile function specifically is less clear — Miyoshi 2023. A separate case-control study in men with benign prostatic hyperplasia found significantly lower serum zinc and testosterone levels in affected patients compared to controls — Radhi 2023. The implication is not that zinc supplementation will raise testosterone in replete individuals; it is that zinc deficiency — which is more prevalent in Western populations than commonly acknowledged — may impair the enzymatic processes involved in testosterone synthesis.
Vitamin D's relationship with testosterone has been examined in multiple systematic reviews and meta-analyses. The association between low vitamin D status and lower androgen levels has been demonstrated in case-control studies, though direct causality remains difficult to establish — D'Andrea 2021. A further review examining vitamin D, testosterone, and depression in middle-aged and elderly men found consistent associations across studies, with the authors noting plausible shared mechanisms involving the hypothalamic-pituitary-gonadal (HPG) axis — Amini 2023.
A 2021 systematic review of herbs and testosterone concentrations in men found that the evidence for most botanical interventions is limited by small sample sizes and methodological heterogeneity — Smith 2021. Ashwagandha (Withania somnifera) emerged as one of the more credible candidates, with some trial data supporting effects on stress-related hormonal disruption, though the authors were appropriately cautious about magnitude of effect.
Oestrogen, Perimenopause, and the Transition Years
The perimenopausal transition — the years preceding the final menstrual period — involves progressive fluctuations in oestrogen and progesterone that affect vasomotor regulation, sleep architecture, mood, cognition, and metabolic function. This is not a deficiency to be corrected so much as a physiological transition to be navigated with evidence-informed support.
A 2026 review in The American Journal of Medicine examined integrative approaches to perimenopause, noting that nutritional strategies including plant-forward diets and phytoestrogen-containing foods may alleviate vasomotor symptoms, while acknowledging that the evidence base for many specific interventions remains incomplete — Kennard 2026. The review underscores what I consider the most important framing for this topic: perimenopause is a nutrition-sensitive period, meaning that the quality of nutritional inputs during this window may have disproportionate effects on long-term health trajectories.
Choline is one nutrient that has received specific attention in the context of cognitive function during the menopause transition. A study using data from the Study of Women's Health Across the Nation found that dietary choline and betaine intake had a modest but measurable association with cognitive performance across the transition — Cowan-Pyle 2024. The effect sizes were not dramatic, but the mechanistic plausibility is strong: oestrogen supports choline biosynthesis, so declining oestrogen during perimenopause may increase dietary choline requirements.
Sex hormones also interact with neurological function in ways that extend well beyond reproduction. A preclinical research panel review on sex hormones and migraine documented how fluctuations in oestrogen and progesterone affect pain processing, autonomic function, and sensory thresholds — Godley 2024. This is relevant not only to migraine sufferers but to anyone seeking to understand why hormonal fluctuations produce such wide-ranging systemic effects.
Ashwagandha has been evaluated specifically in perimenopausal women. A randomised, double-blind, placebo-controlled trial found that a root extract of Withania somnifera produced statistically significant reductions in climacteric symptoms compared to placebo — Gopal 2021. The proposed mechanism involves modulation of the HPA axis rather than direct oestrogenic activity, which is an important distinction.
The Thyroid Axis: Iodine, Selenium, and the Gut Connection
The thyroid gland produces thyroxine (T4) and triiodothyronine (T3), hormones that regulate basal metabolic rate, thermogenesis, cardiac output, and neurological development, among other functions. The synthesis of thyroid hormones is directly dependent on two micronutrients: iodine and selenium. Iodine is the structural component of both T4 and T3; selenium is required for the deiodinase enzymes that convert the relatively inactive T4 into the metabolically active T3.
Iodine deficiency remains the most common preventable cause of thyroid dysfunction globally, and while overt deficiency is uncommon in the UK due to dairy consumption, marginal iodine status is more prevalent than commonly recognised — particularly in those following plant-based diets that exclude dairy and fish. EFSA's NHC register approves the wording "iodine contributes to the normal production of thyroid hormones and normal thyroid function."
Selenium's role extends beyond T4-to-T3 conversion. It is also a component of glutathione peroxidase enzymes that protect the thyroid gland from oxidative stress during hormone synthesis — a process that generates hydrogen peroxide as a by-product. EFSA's NHC register approves the wording "selenium contributes to the normal function of the thyroid gland."
Perhaps the most underappreciated aspect of thyroid function is its relationship with the gut microbiome. A 2021 review in Nutrients documented bidirectional interactions between intestinal microbiota and thyroid function, noting that autoimmune thyroid diseases (Hashimoto's thyroiditis and Graves' disease) frequently co-occur with intestinal conditions, and that gut microbiota composition influences thyroid hormone metabolism and iodine absorption — Knezevic 2021. This gut-thyroid axis is an emerging area of research with significant clinical implications.
Magnesium also warrants mention here. A study examining serum magnesium and thyroid hormones across pre-, peri-, and post-menopausal women found associations between magnesium status and thyroid hormone concentrations — Kolanu 2023. The mechanisms are not fully elucidated, but magnesium is a cofactor in numerous enzymatic reactions, and its relevance to endocrine function extends well beyond the thyroid.
The HPA Axis: Stress, Cortisol, and Downstream Hormonal Effects
The hypothalamic-pituitary-adrenal (HPA) axis is the body's primary stress-response system. Activation of this axis by perceived threat — whether physical, psychological, or metabolic — triggers a cascade culminating in cortisol release from the adrenal cortex. Cortisol is essential for acute stress responses, but chronic HPA activation produces downstream effects on reproductive hormones, thyroid function, insulin sensitivity, and immune regulation that are well-documented in the literature.
The mechanism by which chronic stress suppresses reproductive hormones is relatively well understood: elevated cortisol and corticotropin-releasing hormone (CRH) inhibit gonadotropin-releasing hormone (GnRH) pulsatility at the hypothalamic level, reducing LH and FSH secretion and, consequently, gonadal steroid production. This is one reason why chronic psychological stress is consistently associated with menstrual irregularity in women and reduced testosterone in men.
Adaptogens — a functional category of botanical compounds defined by their capacity to modulate the stress response — have accumulated a credible evidence base in this context. Rhodiola rosea and ashwagandha are the two most studied. A randomised, double-blind, placebo-controlled trial of a standardised ashwagandha root extract in adults experiencing high stress and fatigue found significant reductions in perceived stress scores and associated physiological markers compared to placebo — Smith 2023. The proposed mechanism involves modulation of HPA axis reactivity rather than direct hormonal intervention.
L-theanine, an amino acid found in green tea, has documented effects on stress-related neurological function through its influence on GABAergic and glutamatergic signalling. While the direct HPA axis effects of L-theanine are less extensively studied than those of ashwagandha, its role in attenuating acute stress responses is supported by controlled trial data.
It is worth noting that the stress-hormone relationship is bidirectional: hormonal disruption itself generates physiological stress, which can perpetuate HPA dysregulation. This feedback dynamic is one reason why addressing nutritional deficiencies and sleep quality — both of which affect HPA tone — is often more productive than targeting any single hormone in isolation.
Vitamin D: The Hormone That Isn't Quite a Vitamin
Vitamin D occupies an unusual position in nutritional science: it is technically a prohormone, converted in the liver and kidneys to its active form (1,25-dihydroxyvitamin D3, or calcitriol), which then acts on nuclear receptors in a manner functionally identical to steroid hormones. Vitamin D receptors (VDRs) are present in virtually every tissue in the body, including the testes, ovaries, adrenal glands, and pituitary — which explains why vitamin D status has such wide-ranging endocrine implications.
The relationship between vitamin D and testosterone has been examined in multiple meta-analyses. A 2021 systematic review and meta-analysis found positive associations between vitamin D status and testosterone levels across case-control studies, with the association being particularly pronounced in men with documented vitamin D deficiency — D'Andrea 2021. A further systematic review examining vitamin D, testosterone, and depression in middle-aged and elderly men found consistent co-occurrence of low vitamin D, low testosterone, and depressive symptoms, suggesting shared mechanistic pathways — Amini 2023.
Vitamin D's relationship with prostate cancer progression has also been examined through the lens of testosterone mediation. A systematic review and meta-analysis found that testosterone may partially mediate the association between vitamin D status and prostate cancer outcomes, though the authors noted that direct causality remains difficult to establish — Robles 2022.
In the context of breast cancer survivors, a study examining long-term vitamin D supplementation found that it affected serum testosterone levels in women with early-stage breast cancer over a 24-month period — Minopoli 2025. This is a specific clinical population, and the findings should not be generalised uncritically, but they add to the mechanistic picture of vitamin D as an endocrine-active compound.
UK adults are at particular risk of vitamin D insufficiency: the combination of northern latitude, indoor working patterns, and sun avoidance means that a substantial proportion of the population does not maintain serum 25(OH)D concentrations above the 50 nmol/L threshold associated with adequate endocrine function. EFSA's NHC register approves the wording "vitamin D contributes to the maintenance of normal testosterone levels in the blood" — a claim that reflects the accumulated mechanistic and epidemiological evidence.
B Vitamins, Magnesium, and the Enzymatic Machinery of Hormone Synthesis
Hormones do not synthesise themselves. The enzymatic reactions involved in steroidogenesis, thyroid hormone production, and neurotransmitter synthesis that modulates HPA tone all depend on cofactors — vitamins and minerals that enable or accelerate these reactions. B vitamins and magnesium are among the most important in this context.
Vitamin B6 (pyridoxine) is particularly relevant. Its active form, pyridoxal-5'-phosphate (PLP), is a cofactor in over 150 enzymatic reactions, including the synthesis of serotonin, dopamine, and GABA — neurotransmitters that modulate HPA axis reactivity. A 2025 study in the Journal of Internal Medicine examined PLP's effects on blood pressure regulation through its role in angiotensin II modification, highlighting the breadth of B6's physiological reach beyond its commonly cited roles — Lellig 2025.
EFSA's NHC register approves the wording "vitamin B6 contributes to the regulation of hormonal activity" — a claim that reflects B6's role as a cofactor in steroid hormone receptor modulation and its involvement in the metabolism of homocysteine, which has documented associations with cardiovascular risk in the context of hormonal ageing.
Magnesium's relevance to endocrine function is multifaceted. It is a cofactor in over 300 enzymatic reactions, including those involved in ATP synthesis, protein synthesis, and — critically — the conversion of vitamin D to its active form. Low magnesium status impairs vitamin D activation, which creates a compounding deficiency scenario. The association between magnesium status and thyroid hormone concentrations across menopausal stages adds further mechanistic weight — Kolanu 2023.
Folate and vitamin B12 are required for methylation reactions that affect gene expression, including the expression of hormone receptors. Chromium has a documented role in insulin signalling — EFSA's NHC register approves the wording "chromium contributes to normal macronutrient metabolism and to the maintenance of normal blood glucose levels" — which is relevant to hormonal health given insulin resistance's well-established downstream effects on sex hormone-binding globulin (SHBG) and free testosterone.
Nutraceutical support for blood pressure — which intersects with the renin-angiotensin-aldosterone system (RAAS), a hormonal axis in its own right — has been reviewed by the European Society of Hypertension, which identified several dietary components with meaningful evidence for blood pressure modulation — Borghi 2021. This is a reminder that "hormonal health" extends well beyond the sex steroids that dominate popular coverage.
What KōJō Daily Formula Does for Hormonal Health
KōJō Daily Formula v4.1 was not designed as a "hormone product." It was designed as a comprehensive nutritional foundation — and that distinction matters. The endocrine system does not respond to single-ingredient interventions in the way that supplement marketing implies. It responds to the overall adequacy of the nutritional environment in which it operates.
The following ingredients in KōJō Daily Formula have documented relevance to endocrine function through the mechanisms discussed in this article:
Vitamin D3 — 50mcg Supports the maintenance of normal testosterone levels (EFSA-approved claim). Present in virtually all endocrine tissues via VDR expression. Particularly relevant for UK adults with high insufficiency prevalence.
Zinc Bisglycinate — 53mg (16mg elemental) Low serum zinc is associated with reduced testosterone in multiple studies — Miyoshi 2023, Radhi 2023. Bisglycinate form improves absorption compared to inorganic zinc salts.
Magnesium Bisglycinate — 1000mg (200mg elemental) Cofactor in over 300 enzymatic reactions including vitamin D activation and thyroid hormone metabolism — Kolanu 2023. Bisglycinate form selected for superior bioavailability and gastrointestinal tolerance.
Iodine — 150mcg Required for thyroid hormone synthesis. EFSA approves "iodine contributes to the normal production of thyroid hormones and normal thyroid function." Dose reflects the EU NRV; particularly relevant for those on plant-based diets.
Selenium — 100mcg Required for deiodinase enzymes converting T4 to active T3, and for glutathione peroxidase protection of thyroid tissue during synthesis. EFSA approves "selenium contributes to the normal function of the thyroid gland."
Vitamin B6 — 2.8mg EFSA approves "vitamin B6 contributes to the regulation of hormonal activity." Active as PLP in steroid hormone receptor modulation and neurotransmitter synthesis affecting HPA tone — Lellig 2025.
Vitamin B12 — 500mcg Supports methylation reactions relevant to hormone receptor expression. EFSA approves "vitamin B12 contributes to normal homocysteine metabolism."
Folate — 400mcg Required for one-carbon methylation reactions affecting gene expression and receptor function.
Chromium — 200mcg EFSA approves "chromium contributes to normal macronutrient metabolism and to the maintenance of normal blood glucose levels." Insulin sensitivity is directly relevant to SHBG levels and free sex hormone availability.
Rhodiola Rosea Extract — 350mg Adaptogen with evidence for HPA axis modulation under conditions of chronic stress and fatigue. Supports stress-related hormonal regulation through central rather than peripheral mechanisms.
Choline Bitartrate — 1000mg Dietary choline is associated with cognitive performance during the menopause transition — Cowan-Pyle 2024. Oestrogen supports endogenous choline synthesis; declining oestrogen may increase dietary requirements.
Bacillus coagulans GBI-30, 6086 — 2 billion CFU and Tributyrin — 500mg Support gut microbiome integrity, which is mechanistically relevant to both thyroid function (gut-thyroid axis) — Knezevic 2021 — and oestrogen metabolism via the estrobolome.
N-Acetyl Cysteine — 600mg Precursor to glutathione. Supports antioxidant capacity relevant to thyroid gland protection during hormone synthesis and adrenal function under oxidative stress conditions.
Vitamin A — 750mcg RAE Required for the synthesis of steroid hormones and for the function of nuclear hormone receptors. EFSA approves "vitamin A contributes to the maintenance of normal mucous membranes" and has established roles in reproductive biology.
Moringa Leaf Powder — 2500mg Provides a broad spectrum of micronutrients including iron, calcium, and B vitamins that support the nutritional foundation underlying endocrine function.
The evidence for hormonal health does not point to a single intervention. It points to a nutritional environment in which the enzymatic machinery of the endocrine system has what it needs to function. That is a less satisfying answer than "take this to fix your hormones" — but it is the honest one, and it is what the literature actually supports.
Frequently Asked Questions
The article mentions zinc, magnesium, vitamin D, and iodine matter for hormones. How do I know if I'm actually deficient rather than just low-normal?
Deficiency is a clinical diagnosis, not a marketing category. Marginal status is common but doesn't automatically require supplementation. A GP can order serum testing. The evidence supports addressing genuine deficiency—particularly zinc, vitamin D, and iodine—but supplementing already-replete individuals shows minimal effect on hormone levels.
You cite ashwagandha for both testosterone and perimenopause symptoms. Does it actually work, or is the evidence just 'credible' marketing language?
Ashwagandha has controlled trial data showing measurable effects on stress-related hormonal disruption and climacteric symptoms, but effect sizes are modest, not dramatic. It works through HPA axis modulation, not direct hormone production. It's evidence-informed, not a replacement for addressing sleep, stress, and nutrition fundamentals.
Why does the article keep saying 'documented mechanisms' but then say most testosterone boosters lack evidence? What's the difference?
A documented mechanism means we understand *how* something could work—e.g., zinc is required for testosterone synthesis. That doesn't mean supplementing zinc raises testosterone in healthy people. Most commercial products claim effects without evidence they actually deliver those effects in non-deficient populations.
The gut-thyroid axis is mentioned at the end. Should I be taking probiotics or doing something specific to support it, or is that incomplete?
The gut-thyroid connection is real but emerging. The article notes bidirectional interactions and associations with autoimmune thyroid disease, but doesn't detail specific interventions. Current evidence supports adequate fibre, diverse whole foods, and addressing gut dysbiosis if present—not routine probiotic supplementation.
For perimenopause, you mention choline and phytoestrogens. Is KōJō's formula specifically designed around these nutrients, or am I reading too much into it?
The article establishes the evidence for specific nutrients during perimenopause—choline, phytoestrogens, stress-axis support—but doesn't detail any particular product formulation. Any supplement should be evaluated against this evidence base independently, not assumed to address all mechanisms.
