HGH and Aging: How to Support Growth Hormone After 40 (US Guide)

There’s a multi-billion-dollar anti-aging industry built on a single study of twelve men, published in 1990.

The researcher who ran it spent the rest of his life insisting it meant nothing of the kind. Thirteen years later, the journal that published it printed a rebuke of the companies citing it.

Almost nobody selling you HGH will mention either fact. So let’s start there, and then get to what actually works for a 45-year-old.

The One Study That Started All of This

July 1990. The New England Journal of Medicine publishes Daniel Rudman’s paper: “Effects of Human Growth Hormone in Men over 60 Years Old.”

Twelve men, aged 61 to 81, all with IGF-1 levels below the young-adult range. Six months of growth hormone injections, three times a week.

The results were striking. Lean body mass rose 8.8%. Fat mass fell 14.4%. Skin thickness increased 6.6%.

Those are real numbers from a real study, and they haven’t been overturned. Body composition changed.

What the press did with it

The coverage wrote itself. Muscle up, fat down, skin thicker — three of the most visible markers of aging, apparently reversed in half a year.

Within a few years there were anti-aging clinics, a bestselling book called Grow Young with HGH, and an entire supplement category.

What Rudman actually said

Here’s the part that got lost.

Rudman remained adamant until his death that his study had no implications for anti-aging. His own stated interest was in frail elderly patients recovering from fractures, surgery or pneumonia — people who struggle to rebuild lean tissue after illness.

That’s a narrow clinical question. It is not “reverse aging.”

Twelve men. Six months. One outcome measure. Every serious reader understood the limits at the time — the journal’s own correspondence pages carried letters warning that extrapolating to normal aging “should have been done more carefully.”

The industry extrapolated anyway.

What Happened Next

Two things, and both matter more than the original paper.

The journal turned on the industry

In 2003 the NEJM published two pieces addressing what had been built on Rudman’s study.

One came from Mary Lee Vance — the endocrinologist who had written the accompanying editorial back in 1990. Her 2003 piece was titled “Can Growth Hormone Prevent Aging?”

Her assessment was blunt. Studies since 1990 confirm the body composition effects but do not show improvement in function.

Then the line I’d put on a poster if I ran a gym:

“In contrast, resistance training improves muscle strength and function, indicating that real effort is beneficial.”

That’s the New England Journal of Medicine, in a piece about growth hormone, telling you to go lift something.

She also noted that oral growth hormone preparations “would not be expected to be effective,” since GH is a peptide degraded by stomach acid — a point still worth repeating twenty years later.

The second piece came from the journal’s editor-in-chief and was even more direct about the marketing: if people are buying a “human growth hormone releaser” on the strength of research published in the Journal, they are being misled.

Then came the systematic review

In 2007, Annals of Internal Medicine pooled 18 randomized controlled trials of growth hormone in healthy elderly people.

The conclusion: GH therapy is associated with small changes in body composition and increased rates of adverse events, and on that evidence, cannot be recommended as an anti-aging therapy.

The adverse events weren’t trivial. Soft tissue swelling, joint pain, carpal tunnel syndrome, gynecomastia, and significantly higher rates of impaired fasting glucose and diabetes.

That last one deserves emphasis. Growth hormone is diabetogenic — it raises blood sugar. Giving it to a 60-year-old with borderline glucose control is not a neutral act.

The Paradox Nobody in the Industry Mentions

Now the finding that genuinely complicates this topic, and which I’ve never seen on a page selling HGH.

Less growth hormone signaling is associated with longer life in every animal model where it’s been tested.

Mice with defective GH production or GH resistance live markedly longer than normal mice. Transgenic mice engineered to have grossly elevated GH and IGF-1 are short-lived and show signs of accelerated aging.

Deleting a protein that increases IGF-1 availability also extends mouse lifespan.

In humans, people with congenital GH deficiency appear to have reduced rates of some age-related diseases.

Sitting with the contradiction

So we have a hormone that declines with age, whose decline correlates with the visible signs of aging — and whose suppression extends lifespan in animals.

Both things appear to be true. GH supports function and body composition in the near term, while chronic elevation of the GH/IGF-1 axis appears to accelerate biological aging over a lifetime.

I don’t think anyone has fully reconciled this. What I’d take from it is a specific kind of humility.

Raising your growth hormone as high as possible is not obviously the goal. Restoring what your lifestyle has suppressed is a defensible aim. Pushing beyond your natural ceiling with injections is a bet against a body of evidence pointing the other way.

That distinction runs through the rest of this article.

So Should You Care About GH After 40 At All?

Yes — but for the right reasons, on the right timescale.

Growth hormone genuinely supports things a man in his forties cares about:

• Fat metabolism — GH is strongly lipolytic
• Connective tissue — tendons, ligaments, cartilage and skin all depend on GH-driven collagen synthesis
• Recovery — tissue repair, largely during deep sleep
• Bone density — ongoing remodeling and mineral retention
• Body composition — the visceral fat and lean mass balance

None of that is about living to 100. It’s about your joints not aching, recovering from a hard session in two days instead of five, and not watching your waistband creep every year.

That’s a reasonable goal, and lifestyle gets you most of the way there.

What Actually Declines, and When

This is the part that surprises men most, and it changes when you should act.

The standard story says GH declines steadily from your twenties, roughly 14–15% per decade. True, but it hides something important: the decline is front-loaded.

A study of 149 healthy men aged 16 to 83 tracked both sleep architecture and hormones, and found two distinct phases.

Early adulthood to midlife (roughly 25 to 45). Deep slow-wave sleep collapsed from about 18.9% of the night to just 3.4%. Over that same window, GH secretion fell by roughly 372 micrograms per decade.

Midlife to late life (roughly 50 to 80). Slow-wave sleep didn’t fall much further — there wasn’t much left. GH continued declining, but at only about 43 micrograms per decade.

Read those two numbers side by side.

The overwhelming majority of the growth hormone you lose in a lifetime is lost before you turn 50 — and it tracks the collapse of your deep sleep almost exactly.

Why this matters if you’re 42

Most men start thinking about this at 55, once the mirror forces the issue. By then, most of the decline has already happened.

Your forties are the highest-leverage window you will ever have. Not your sixties.

There’s a second detail worth knowing. The men in that study had no sleep complaints and no diagnosed sleep disorders. Their deep sleep collapsed anyway.

So “I sleep fine” isn’t reassurance. It’s usually a statement about total hours — the one number that stayed stable while the valuable part disappeared.

Are You Actually Deficient?

Important distinction, and clinics blur it deliberately.

Somatopause is the normal age-related decline in GH. It happens to everyone. It is not a disease.

Adult growth hormone deficiency is a clinical condition, usually caused by pituitary tumors, pituitary surgery, cranial radiation, or significant head trauma. It’s diagnosed with stimulation testing and treated by endocrinologists.

The anti-aging pitch collapses these two. It compares your IGF-1 to a 25-year-old’s range, declares a “deficiency,” and offers treatment.

By that logic, every man over 40 is deficient — which is another way of saying the term has stopped meaning anything.

	SomatopauseWhat almost every man over 40 has	Adult GH DeficiencyA genuine clinical condition
What it is	Normal age-related decline in growth hormone. Universal, gradual, and not a disease.	Pathological failure of the pituitary to produce adequate growth hormone.
What causes it	Ageing, plus the things you control — collapsing deep sleep, rising visceral fat, insulin resistance, chronic stress.	Pituitary tumour or surgery, cranial radiation, significant head trauma, or certain genetic conditions.
Who has it	Essentially everyone, to some degree. Though research on people over 69 found a substantial proportion still secrete normally.	Rare. It doesn’t arrive quietly with your fortieth birthday — there’s usually an identifiable cause in your medical history.
How it’s identified	It isn’t diagnosed, because it isn’t a diagnosis. Clinics manufacture one by comparing your IGF-1 to a 25-year-old’s reference range.	Stimulation testing — insulin tolerance, glucagon or macimorelin — ordered and interpreted by an endocrinologist.
What to do	Sleep, visceral fat, training, eating window — the five levers, in order.	See an endocrinologist. GH replacement here is legitimate medicine with a real evidence base.

Why the distinction matters commercially. If your IGF-1 is measured against a young adult’s range, every man over 40 is “deficient” — which is another way of saying the word has stopped meaning anything. Always ask for age-adjusted ranges, and read a low result alongside your testosterone, thyroid, fasting insulin and HbA1c before concluding anything about your pituitary.

What the data says about “deficient” older men

Research on people over 69 found that a substantial proportion still secrete growth hormone normally. Chronological age doesn’t reliably predict your GH status.

Which is a good argument for testing before assuming, and a better argument for not assuming at all.

Testing that’s actually useful

Don’t order a random serum GH test. GH is released in pulses, and between pulses it can be undetectable in a perfectly healthy man.

IGF-1 is the practical proxy — longer half-life, more stable through the day. Compare against age-adjusted reference ranges, not the broad lab range.

Run these alongside it, because they’ll usually explain more than the IGF-1 does:

• Total and free testosterone, plus SHBG
• Full thyroid panel
• Fasting insulin and HbA1c
• Comprehensive metabolic panel and lipids
• Vitamin D, ferritin, B12

If your fasting insulin is elevated and your IGF-1 is low, you very likely don’t have a pituitary problem. You have a metabolic one — and that’s genuinely better news, because it responds to what you do.

See an endocrinologist if you have a history of pituitary tumor, head trauma or cranial radiation, or if IGF-1 sits well below the age-adjusted range on repeat testing.

The Five Levers That Actually Work

Ranked by how much they move the needle. Notice that the NEJM‘s own answer to anti-aging HGH — real effort — sits at number three, and the two above it are free.

Lever	Impact	What to actually do
1Sleep ~70% of daily output happens in early sleep	Highest	Fixed wake time seven days a week. Room 65–68°F, blacked out, no alcohol within three hours of bed. Get screened for sleep apnoea if you snore — CPAP has been shown to raise IGF-1 in men averaging 56.
2Visceral fat Suppresses secretion directly — and reversibly	Highest	Target a waist under half your height. Waist-to-height beats BMI here because it’s visceral fat specifically doing the suppressing.
3Training intensity The lever the NEJM itself pointed to	High	Three resistance sessions, 60–90 sec rest on accessories. One conditioning session: 4–6 × 30-second bike or rower sprints. Skip flat-ground sprinting after 40 — same stimulus, far more hamstrings.
4Fasting window Still works on an aging axis	Moderate	16:8 most days, with an occasional 24-hour fast. Older adults showed roughly a four-fold GH increase after two days of fasting — comparable in fold-change to young men.
5Food Removes suppression rather than driving output	Supporting	Finish eating three hours before bed, keep evening carbs low, hit 0.7–1.0g protein per pound of target bodyweight. Older muscle needs the higher end.

Work down the list, don’t cherry-pick. The top two are free, and between them they account for most of what a man in his forties can actually change. Notice too what isn’t on this list — nothing you can buy appears above number five, and that ordering is the whole argument of this article.

1. Sleep

Roughly 70% of daily GH output happens during early sleep, and in men the pulse fired shortly after sleep onset is often the largest secretory episode of the day.

Given that deep sleep collapse tracks the GH collapse almost exactly, this is the single highest-return intervention available to you. Fixed wake time, cold dark room, no alcohol within three hours of bed.

And if you snore heavily or wake unrefreshed, get screened for sleep apnea before you spend money on anything else — consistent CPAP use has been shown to raise IGF-1 measurably in men averaging 56 years old.

The full mechanism, and the protocol, is in our guide to how sleep affects HGH production.

2. Visceral fat

Belly fat directly suppresses GH secretion through elevated insulin, free fatty acids and increased somatostatin tone. And low GH makes visceral fat easier to store, so the loop compounds.

The encouraging part is that this is functional rather than structural. The GH-axis abnormalities associated with obesity are largely reversible with weight loss.

Waist under half your height is a reasonable first target, and it beats BMI because it’s visceral fat specifically doing the suppressing.

3. Training intensity

This is the lever the NEJM pointed to, and the evidence has held up.

Sprint intervals produce the largest acute response — a 30-second maximal effort produced peak GH of 18.5 µg/L versus 4.0 µg/L for a 6-second one. In the gym, 60-second rest between sets produced 64% more GH than 120-second rest.

One honest caveat that matters more after 40 than before: the acute spike is excellent for fat metabolism and connective tissue, but it doesn’t appear to drive muscle growth directly. Train hard because hard training builds muscle, and take the hormone response as a bonus. The full protocol is in our breakdown of the exercises that boost growth hormone.

4. Fasting windows

Fasting produces the most dramatic acute GH numbers of anything on this list — and it still works on an aging axis. Studies in older adults found roughly a four-fold increase in GH production after two days of fasting, comparable in fold-change to young men.

There’s a significant catch in what happens downstream, though, which changes how you should use it. We cover that in does fasting increase HGH.

5. Food

Fifth, and honestly so. Food’s main contribution is controlling insulin — GH’s direct antagonist — and supplying protein to support the GH/IGF-1 axis.

Finish eating three hours before bed, keep evening carbs low, and hit your protein target. The specifics, including which “HGH foods” are fiction, are in our guide to foods that boost HGH naturally.

For how all five fit together into one system, our complete framework covers how to increase HGH naturally.

What Changes After 40

The levers are the same. How you apply them isn’t.

Recovery becomes the constraint, not effort. Three genuinely hard sessions a week beats six mediocre ones you never recover from. Cortisol is GH’s antagonist, and chronic overreaching produces a worse hormonal profile than training less.

Injury risk reshapes your exercise selection. Maximal flat-ground sprinting is where men over 40 tear hamstrings. Bike sprints, rower intervals and sled pushes deliver the same metabolic stimulus with a fraction of the risk.

Sleep needs active management, not hope. In your twenties you slept deeply by default. After 40 you have to engineer it — temperature, light, alcohol, timing.

Protein requirements go up, not down. Anabolic resistance means older muscle responds less to the same protein dose. Aim toward the higher end of 0.7–1.0 g per pound of target bodyweight.

Test before you assume. Symptoms of low GH overlap almost completely with low testosterone, hypothyroidism, sleep apnea, depression and iron deficiency. Guessing is expensive.

The Anti-Aging Clinic Playbook

If you’ve searched this topic, you’ve seen the pitch. It follows a reliable script.

Step one: compare your IGF-1 to young-adult reference ranges rather than age-adjusted ones. Step two: call the gap a deficiency. Step three: offer treatment.

Here’s what those pages leave out.

The legal reality

In the US, distributing human growth hormone for anti-aging, athletic or performance purposes — as opposed to a recognized medical condition — is a federal offense under 21 U.S.C. § 333(e), carrying up to five years’ imprisonment.

The FDA has taken the position that writing a prescription for an unauthorized use constitutes distribution under that statute. Anti-aging clinic operators have been federally prosecuted for exactly this, and a few states go further and criminalize possession.

Prescription somatropin is a legitimate medicine for a narrow set of conditions: pituitary disease, Turner and Prader-Willi syndromes, short bowel syndrome, HIV wasting. Being 52 and tired is not on that list.

And the evidence reality

Even setting the law aside — 18 randomized trials, pooled, produced small body composition changes and significantly more adverse events, and the reviewers concluded GH cannot be recommended as an anti-aging therapy.

Where legal alternatives fit

No oral supplement contains growth hormone. It’s a peptide, and stomach acid destroys it — a point the NEJM made explicitly in 2003 and which remains true today.

Legitimate products are secretagogues that support your own production. A few ingredients have real human data, most formulas underdose them, and none of them substitute for sleep, training and body fat. If you’re at the point where the fundamentals are handled and you want to evaluate what’s on the market, our breakdown of the best legal HGH alternatives goes through which ones disclose their doses honestly.

What About Peptides? CJC-1295, Ipamorelin and the Rest

This section exists because the pitch has changed.

Ask around the anti-aging world today and fewer clinics lead with HGH itself. They lead with peptides — CJC-1295, ipamorelin, sermorelin, GHRP-2 and GHRP-6, or oral MK-677.

The framing is appealing: rather than injecting the hormone, you’re “gently encouraging your own pituitary.” It sounds like a smarter, safer middle path.

The regulatory picture is a lot messier than that, and almost nobody selling them explains it.

What they actually are

Two broad families, both acting upstream of growth hormone rather than replacing it.

GHRH analogues — sermorelin, CJC-1295, tesamorelin. These mimic growth hormone releasing hormone, the signal your hypothalamus sends to the pituitary.

Ghrelin mimetics / secretagogues — ipamorelin, GHRP-2, GHRP-6, MK-677 (ibutamoren). These act on the ghrelin receptor, a separate pathway that also triggers GH release.

Clinics often combine one from each family, on the logic that hitting two pathways beats one. Biologically that reasoning isn’t unreasonable. Regulatorily, it’s a different story.

The regulatory reality, in order

Follow the sequence, because the middle step gets misrepresented constantly.

September 2023. The FDA placed a long list of these compounds in Category 2 of its interim 503A bulk substances list — the category for substances that raise significant safety concerns. CJC-1295, ipamorelin acetate, ibutamoren mesylate and BPC-157 were all on it.

Category 2 means compounding pharmacies cannot legally use them.

September 2024. Five substances were removed from Category 2, including CJC-1295 and ipamorelin. This is the step you’ll see cited as vindication.

It wasn’t. They were removed because the original nominators withdrew their nominations — an administrative change, not a safety clearance. Nothing about the FDA’s concerns was resolved.

Late 2024. At the advisory committee meetings that followed, the FDA published its analyses and recommended that ipamorelin, ibutamoren and kisspeptin-10 not be included in the 503A bulks regulation.

Where that leaves things. CJC-1295 and ipamorelin have no approved brand, no approved indication, and cannot be legally compounded under Section 503A.

The comparison that clarifies everything

Here’s the detail that cuts through the marketing.

Tesamorelin is FDA-approved. It’s sold as Egrifta, and it’s a GHRH analogue — the same broad family as CJC-1295.

So an approved GH-axis peptide does exist. Its approved indication is HIV-associated lipodystrophy, a specific medical condition. Not anti-aging.

Sermorelin has its own history — previously approved as Geref, since discontinued.

Which tells you the FDA isn’t hostile to this class in principle. It has approved one, for a defined condition, with a defined evidence base. The compounds being marketed to healthy men in their forties are simply not that.

The practical risks

Sourcing is unverifiable. If a compound can’t legally be compounded, whatever your clinic is dispensing came from somewhere outside that framework. Purity, dose accuracy and sterility are unverifiable.

Naming is slippery. “CJC-1295” refers to more than one molecule — the version with a drug affinity complex behaves very differently from the version without. The FDA’s own evaluations treated them separately. A vendor using shorthand may be selling you something other than what you think.

Long-term human data barely exists. Most of what’s known concerns short-term hormonal response, not multi-year outcomes in healthy middle-aged men.

And the underlying question doesn’t go away. If raising GH signalling as high as possible were straightforwardly good, the longevity data we covered earlier would look different than it does.

What this section isn’t

It isn’t a protocol, and it isn’t a recommendation either way. I’ve deliberately given no doses, no stacking guidance and no sourcing.

If you have a diagnosed condition that a GH-axis peptide is approved to treat, that’s a conversation with a physician. If you’re a healthy 45-year-old whose main complaint is tiredness and a thicker waist, you’re being marketed an unapproved drug for an indication that doesn’t exist.

Regulatory status in this area genuinely moves. This section reflects the position as of publication — verify current FDA guidance before acting on anything here.

A 90-Day Plan for Men Over 40

Layered deliberately. Each phase makes the next easier.

Weeks 1–3 — Sleep only. Fixed wake time seven days a week. Room at 65–68°F, blacked out. No alcohol within three hours of bed. Ten minutes of outdoor light within thirty minutes of waking. If you snore, book the sleep study now.

Weeks 4–6 — Add training. Three resistance sessions built on compound lifts, 60–90 seconds rest on accessories. One conditioning session: 4–6 × 30-second bike or rower sprints with full passive recovery.

Weeks 7–9 — Add the eating window. Settle into 16:8. Protein first, evening carbs low, last meal three hours before bed. One 24-hour fast if you tolerate it and aren’t on glucose-lowering medication.

Weeks 10–12 — Measure and reassess. Waist circumference, morning energy, recovery time, strength numbers. Then bloods: IGF-1 age-adjusted, testosterone, thyroid, fasting insulin, HbA1c.

What to expect, honestly. Sleep quality shifts in week one or two. Recovery improves by week four to six. Body composition moves around month three. Lab markers lag furthest behind — which is exactly why most men quit before they see them.

Frequently Asked Questions

Does HGH really decline with age?

Yes, but not evenly. Research tracking 149 healthy men found GH secretion falling around 372 micrograms per decade between early adulthood and midlife, then only about 43 micrograms per decade after — so most of the loss happens before 50, tracking the collapse in deep sleep.

Can I raise my HGH naturally after 40?

Yes. Fasting studies in older adults produced roughly a four-fold increase in GH production, comparable in fold-change to young men. Sleep, training intensity and visceral fat loss all still work — from a lower baseline, but the mechanisms are intact.

Is HGH therapy good for anti-aging?

The evidence says no. A systematic review of 18 randomized trials in healthy elderly people found small body composition changes with significantly increased adverse events, and concluded GH cannot be recommended as an anti-aging therapy.

Is it legal to get HGH for anti-aging in the US?

No. Distributing HGH for anti-aging or performance purposes is a federal offense carrying up to five years’ imprisonment, and the FDA treats writing such a prescription as distribution. It’s approved only for specific medical conditions.

Does low HGH mean I’ll age faster?

Not straightforwardly. Reduced GH signaling extends lifespan in animal models, and mice engineered with high GH and IGF-1 are short-lived with accelerated aging. Supporting function is a reasonable goal; maximizing the hormone is not obviously one.

What’s the difference between somatopause and GH deficiency?

Somatopause is the normal age-related decline everyone experiences. Adult GH deficiency is a clinical condition, usually from pituitary disease, injury or radiation, diagnosed by stimulation testing. Clinics frequently blur the two.

What test should I ask my doctor for?

Age-adjusted IGF-1 rather than a random serum GH, since GH is pulsatile and often undetectable between pulses. Run testosterone, thyroid, fasting insulin and HbA1c alongside it — they usually explain more.

The Bottom Line

An industry worth billions rests on twelve men studied for six months in 1990 — and the researcher behind it said, repeatedly and until his death, that it meant no such thing.

The journal that published it printed a rebuke in 2003. A systematic review of 18 trials concluded in 2007 that GH cannot be recommended as an anti-aging therapy. And in every animal model tested, less GH signaling means a longer life.

That’s the honest state of the evidence, and almost nobody selling you something will tell you any of it.

What’s left is genuinely useful. Most of your lifetime GH decline happens before 50 and tracks your deep sleep, which means your forties are the leverage point and sleep is the lever.

Fix that first. Then lose the visceral fat, train hard three times a week, keep a sensible eating window, and stop eating three hours before bed.

That’s not a compromise version of the injectable protocol. It’s what the New England Journal of Medicine concluded when it looked at the whole question — that real effort is what actually improves function.

Start tonight: set one wake time and hold it for three weeks. Everything else on this page gets easier once that’s in place.

This article is for informational purposes and is not medical advice. Consult a licensed physician before starting any fasting protocol, high-intensity exercise program, or supplement regimen — particularly if you are over 40 and previously sedentary, take medication affecting blood sugar, or suspect a hormone deficiency.

References

The founding study and the response to it

1. Rudman D, Feller AG, Nagraj HS, et al. Effects of human growth hormone in men over 60 years old. N Engl J Med. 1990;323(1):1–6. — https://www.nejm.org/doi/full/10.1056/NEJM199007053230101
2. Vance ML. Growth hormone for the elderly? N Engl J Med. 1990;323(1):52–54 (original accompanying editorial). — https://www.nejm.org/doi/full/10.1056/NEJM199007053230109
3. Vance ML. Can growth hormone prevent aging? N Engl J Med. 2003;348(9):779–780. — https://www.nejm.org/doi/full/10.1056/NEJMp020186
4. Correspondence on Rudman et al., N Engl J Med. 1990. — https://www.nejm.org/doi/abs/10.1056/NEJM199011293232212
5. Overview of the surrounding controversy, including the 2003 editorials. — https://en.wikipedia.org/wiki/HGH_controversies

Evidence for GH in healthy older adults

6. Liu H, Bravata DM, Olkin I, et al. Systematic review: the safety and efficacy of growth hormone in the healthy elderly. Ann Intern Med. 2007;146(2):104–115. — https://pubmed.ncbi.nlm.nih.gov/17227934/
7. DARE quality-assessed abstract of the above. — https://www.ncbi.nlm.nih.gov/books/NBK74769/
8. Growth Hormone and Aging. Endotext, NCBI Bookshelf. — https://www.ncbi.nlm.nih.gov/books/NBK279163/

The GH/IGF-1 longevity paradox

9. Junnila RK, List EO, Berryman DE, Murrey JW, Kopchick JJ. The GH/IGF-1 axis in ageing and longevity. Nat Rev Endocrinol. 2013;9(6):366–376. — https://pubmed.ncbi.nlm.nih.gov/23591370/
10. Bartke A. Growth hormone and aging: a challenging controversy. Clin Interv Aging. 2008;3(4):659–665. — https://pmc.ncbi.nlm.nih.gov/articles/PMC2682398/

Age-related decline and sleep

11. Van Cauter E, Leproult R, Plat L. Age-related changes in slow wave sleep and REM sleep and relationship with growth hormone and cortisol levels in healthy men. JAMA. 2000;284(7):861–868. — https://pubmed.ncbi.nlm.nih.gov/10938176/
12. Toogood AA, O’Neill PA, Shalet SM. Beyond the somatopause: growth hormone deficiency in adults over the age of 60 years. J Clin Endocrinol Metab. 1996;81(2):460–465. — https://academic.oup.com/jcem/article/81/2/460/2649335
13. The impact of continuous positive airway pressure on circulating IGF-1 in patients with obstructive sleep apnea. J Clin Sleep Med. 2018. — https://pubmed.ncbi.nlm.nih.gov/29458693/

Fasting, exercise and body fat

14. Hartman ML, Pezzoli SS, Hellmann PJ, et al. Pulsatile growth hormone secretion in older persons is enhanced by fasting. J Clin Endocrinol Metab. 1996;81(7):2694–2701. — https://pubmed.ncbi.nlm.nih.gov/8675598/
15. Stokes KA, Nevill ME, Hall GM, Lakomy HKA. The time course of the human growth hormone response to a 6 s and a 30 s cycle ergometer sprint. J Sports Sci. 2002;20(6):487–494. — https://pubmed.ncbi.nlm.nih.gov/12137178/
16. Rahimi R, et al. Effects of very short rest periods on hormonal responses to resistance exercise in men. J Strength Cond Res. 2010. — https://pubmed.ncbi.nlm.nih.gov/20555276/
17. Rasmussen MH. Obesity, growth hormone and weight loss. Mol Cell Endocrinol. 2010. — https://www.sciencedirect.com/science/article/abs/pii/S0303720709004377

Legal status

18. 21 U.S. Code § 333 — Penalties. Cornell Legal Information Institute. — https://www.law.cornell.edu/uscode/text/21/333
19. U.S. DOJ. Owner and operator of anti-aging center sentenced for distributing growth hormones. — https://justice.gov/usao-wdla/pr/owner-and-operator-anti-aging-center-sentenced-distributing-growth-hormones