2011JAMA
Leproult & Van Cauter
10 healthy young men
One week of sleeping 5 hours a night cut daytime testosterone by 10–15%, similar to 10–15 years of ageing.
Find on PubMed ↗Research library · Hormones & inner health
Hormones: your body's messengers
Cortisol, insulin, testosterone, oestrogen, thyroid hormone and melatonin set your energy, mood, muscle and sleep. Everyday habits move them more than most people realise, and some changes with age deserve a proper medical check.
Good evidenceUpdated Oct 2026 · 4 new studies−10–15%testosterone after one week of 5-hour nights in healthy young menLeproult 2011, JAMA
5.2kmen in TRAVERSE: testosterone for low levels didn't raise heart attacks or strokesLincoff 2023, NEJM
up to 75%of women get hot flushes around menopauseThe Menopause Society, 2022 statement
01
The basics
A slow, chemical messaging system
Hormones are chemical messages released by glands into your blood. Your brain's hypothalamus and pituitary act as control centres, sending signals to the thyroid, adrenal glands, ovaries and testes, which then send hormones to the rest of the body.
Many hormones follow a daily rhythm. Cortisol peaks 30–45 minutes after waking to get you going and falls through the day. Melatonin rises after dark to prepare you for sleep. Late nights, bright evening light and irregular schedules blur both curves.
Sex hormones change with age. Men's testosterone falls slowly from about 40, faster with belly fat and poor sleep. Women's oestrogen drops over a few years around menopause (average age 51), which can bring hot flushes, poor sleep, mood changes, and faster bone and heart changes.
Your daily hormone rhythm
Cortisol peaks soon after waking to get you going. Melatonin rises after dark to prepare you for sleep. Light timing keeps both on schedule.
02
How it works
How a hormone message travels
1
Brain sends a signal
The hypothalamus and pituitary sense what the body needs.
2
Gland releases hormone
Thyroid, adrenals, pancreas, ovaries or testes respond.
3
Travels in blood
The hormone reaches every organ within minutes.
4
Cells respond
Only cells with the matching receptor 'hear' the message.
03
Measure it
Tests worth asking about
- Thyroid (TSH): if you have tiredness, weight change, feeling cold or hot, or hair changes.
- Testosterone (men): a fasting morning test, repeated if low, plus symptoms (low sex drive, erection problems, fatigue). One low result isn't a diagnosis.
- Menopause: over 45 it's usually diagnosed from symptoms; blood tests are mainly useful when younger.
- Insulin and HbA1c: see the blood sugar page. Insulin resistance often comes years before high sugar.
Try your number
LowTypicalHigh
1001100
Morning test. Typical adult range about 264–916 ng/dL (CDC-harmonised). Divide by 28.8 for nmol/L. Diagnosis needs symptoms plus two low results.
04
What the research says
The key studies
2023NEJM
Lincoff et al. (TRAVERSE)
5,246 men aged 45–80
In men with low testosterone and heart risk, testosterone gel did not increase major heart events over about 3 years, though some side effects (such as atrial fibrillation) were more common.
Find on PubMed ↗2024JAMA
Manson et al.
Review of Women's Health Initiative trials
Menopause hormone therapy is reasonable for bothersome symptoms in healthy women under 60 or within 10 years of menopause, but isn't advised just to prevent disease.
Find on PubMed ↗2017NEJM
Stott et al. (TRUST)
737 adults over 65
Thyroid pills for mild (subclinical) underactive thyroid didn't improve symptoms or tiredness.
Find on PubMed ↗2013European Journal of Endocrinology
Corona et al.
24 studies
Weight loss raised testosterone in men with obesity, more so with larger weight loss.
Find on PubMed ↗05
New in 2025–26
What the newest research adds
Regulators have rewritten the rules on hormone therapy. The US removed the long-standing boxed warnings on menopause HRT about heart disease, breast cancer and dementia, and dropped the heart warning on testosterone after TRAVERSE. A 2025 review found HRT neither raises nor lowers dementia risk.
The new studies, in order
Every study added to this page since January 2025. Green rings are the strongest evidence: large trials or meta-analyses.
Testosterone and the heart (TRAVERSE)
5,246 men with low testosterone. Share who had a heart attack, stroke or heart death. The result led the FDA to drop its heart warning in 2025.
NewFeb 2026FDA announcement
US FDA (menopause hormone therapy labels)
Label changes, first 6 products
Following a November 2025 announcement, the FDA approved removal of heart disease, breast cancer and probable dementia from the boxed warning on menopause HRT. It now suggests starting systemic HRT for symptoms in women under 60 or within 10 years of menopause; the womb cancer warning stays for oestrogen-only pills.
Good evidenceRead the source ↗
NewDec 2025Lancet Healthy Longev
Melville et al.
1 trial and 9 observational studies, 1,016,055 women
Menopause hormone therapy was not linked to dementia or mild memory problems, either up or down, whatever the timing, type or length of use. The evidence was mostly low certainty, so HRT should not be taken to protect the brain.
Good evidenceRead the source ↗
NewFeb 2025FDA safety communication
US FDA (testosterone labels)
Class-wide label change based on TRAVERSE
The FDA removed the boxed warning about heart attacks and strokes from testosterone products, as TRAVERSE found no extra risk in men with low testosterone. It added a blood pressure warning to all products, since monitoring studies showed testosterone raises blood pressure.
Strong evidenceRead the source ↗
NewJun 2026HHS announcement
US HHS/FDA (testosterone proposal)
Proposed label changes
HHS proposed dropping the warning that testosterone is unproven for age-related low testosterone and narrowing the prostate cancer warning. Experts caution that tiredness and low mood are often not due to low testosterone, so blood tests and monitoring still matter.
Good evidenceRead the source ↗
What this changes for you
For menopause symptoms, HRT started under 60 or within 10 years of menopause is now seen as safe for most women; talk it through with your doctor. Don't take it to protect your brain. Testosterone is for proven low levels with symptoms, and needs blood pressure checks.
06
Take action
Habits that keep hormones in balance
Sleep, light, muscle and waistline do more than any 'booster'.
- 1
Sleep 7–9 hours
Testosterone, growth hormone and appetite hormones all depend on it.
- 2
Bright light in the morning
Sets your cortisol peak early and melatonin on time at night.
- 3
Lift and move
Muscle makes you more sensitive to insulin and supports healthy testosterone.
- 4
Lose belly fat
Visceral fat turns testosterone into oestrogen and drives insulin resistance.
- 5
Talk about menopause
Hormone therapy and non-hormonal options are effective; ask early rather than putting up with symptoms.
- 6
Test, don't guess
Symptoms plus proper blood tests, not online quizzes or saliva kits.
07
Myth or fact
Common myths, checked
✕ Myth'Adrenal fatigue' explains tiredness.
✓ FactIt isn't a recognised condition; a systematic review found no evidence for it. Real causes include poor sleep, depression, anaemia and thyroid problems.
✕ MythTestosterone boosters work.
✓ FactMost over-the-counter boosters have little or no evidence and some contain hidden drugs.
✕ MythHormone therapy causes breast cancer in everyone.
✓ FactRisk depends on the type, timing and length of use. For many women under 60, benefits outweigh risks.
✕ MythSoy lowers men's testosterone.
✓ FactMeta-analyses of human studies find no effect at normal intakes.
08
Questions
Frequently asked
Should I test my cortisol?
Only if a doctor suspects a gland problem. Single cortisol tests swing a lot through the day.
What is perimenopause?
The 4–10 years before periods stop, when hormones fluctuate. Symptoms can start in the early 40s.
Can men have a 'menopause'?
Testosterone falls gradually, not suddenly. Low levels with symptoms can be treated after proper testing.
09
Test yourself
True, partly true or myth?
Read each claim and pick an answer: the card flips to show the verdict and why. Not sure? Use “Just reveal”.
Card № 01True or myth?
Testosterone in men falls by roughly 1% a year from around age 40.
True
Testosterone in men falls by roughly 1% a year from around age 40.
The fall is gradual; obesity, poor sleep and illness lower it faster than age alone.
Card № 02True or myth?
One week of sleeping 5 hours a night lowered young men's testosterone by 10–15%.
True
One week of sleeping 5 hours a night lowered young men's testosterone by 10–15%.
Leproult & Van Cauter 2011 found this in healthy men in their 20s.
Card № 03True or myth?
Menopause only affects hot flushes.
Myth
Menopause only affects hot flushes.
Falling oestrogen also affects sleep, mood, bones, joints, heart risk, skin and the bladder.
Card № 04True or myth?
Hormone therapy for menopause causes breast cancer.
Partly true
Hormone therapy for menopause causes breast cancer.
Combined HRT slightly raises breast cancer risk with long use; oestrogen-only HRT barely does. For most women under 60 the benefits outweigh the risks.
Card № 05True or myth?
Thyroid problems are much more common in women.
True
Thyroid problems are much more common in women.
Women are about 5–8 times more likely to have thyroid disease, especially an underactive thyroid.
Card № 06True or myth?
Adrenal fatigue is a recognised medical condition.
Myth
Adrenal fatigue is a recognised medical condition.
Endocrine societies say there's no evidence for it. Tiredness has many other, testable causes.
Card № 07True or myth?
Strength training and losing excess fat can raise low testosterone in men.
True
Strength training and losing excess fat can raise low testosterone in men.
Fat tissue converts testosterone to oestrogen, so weight loss often lifts levels.
Card № 08True or myth?
Testosterone boosters from supplement shops work.
Partly true
Testosterone boosters from supplement shops work.
Most have no good evidence. Zinc or vitamin D only help if you were deficient.
Card № 09True or myth?
Insulin is a hormone, and insulin resistance is one of the most common hormone problems.
True
Insulin is a hormone, and insulin resistance is one of the most common hormone problems.
It affects metabolism, fat storage and, in women, is closely tied to PCOS.
Card № 10True or myth?
Low libido is always caused by low hormones.
Myth
Low libido is always caused by low hormones.
Stress, sleep, mood, relationships and medicines are often bigger causes.
Nothing here yet. Try another filter.
10
Sources
References and related topics
- Leproult & Van Cauter (2011). JAMA. 10 healthy young men. PubMed ↗
- Lincoff et al. (TRAVERSE) (2023). NEJM. 5,246 men aged 45–80. PubMed ↗
- Manson et al. (2024). JAMA. Review of Women's Health Initiative trials. PubMed ↗
- Stott et al. (TRUST) (2017). NEJM. 737 adults over 65. PubMed ↗
- Corona et al. (2013). European Journal of Endocrinology. 24 studies. PubMed ↗
- US FDA (menopause hormone therapy labels) (2026). FDA announcement. Label changes, first 6 products. Source ↗
- Melville et al. (2025). Lancet Healthy Longev. 1 trial and 9 observational studies, 1,016,055 women. Source ↗
- US FDA (testosterone labels) (2025). FDA safety communication. Class-wide label change based on TRAVERSE. Source ↗
- US HHS/FDA (testosterone proposal) (2026). HHS announcement. Proposed label changes. Source ↗