If you are a man over 40 and you have started looking into low testosterone, you are not wrong to look there. The decline is real and the symptoms are real. But most men reading this have had their testosterone measured at least once and have never had this second hormone checked a single time in their life. This is about what that hormone is, why it matters as much as testosterone, and what you can actually do about it.

Research suggests testosterone declines by roughly one to two percent per year starting sometime in your 30s. That sounds small in a single year. Stretch it across a decade and the picture changes. By the time a man is 40, that slow decline has been quietly stacking up for ten years or more, and the effects start becoming hard to ignore.

The symptoms men search for are real and worth taking seriously. Lower drive. A flatter mood, where things that used to land just do not hit the same way. Fatigue that a full night of sleep does not seem to fix. Losing muscle while gaining fat, even when nothing about your diet or training has obviously changed. If that sounds like you, getting your testosterone tested is a reasonable and useful step, and nobody should talk you out of it.

Here is where most of the conversation stops. Test testosterone, and if it is low, treat testosterone. That is not wrong. It is just incomplete, because testosterone is not the only hormone declining on that same slow curve, and it is not the only one behind the symptoms above.

The second hormone is called IGF-1. That stands for insulin-like growth factor 1, which is a mouthful, so here is the plain version of what it is and where it comes from.

Your body makes growth hormone, mostly in bursts, called pulses, while you are in deep sleep. Growth hormone does not carry out most of its work directly. Instead it travels to your liver and tells the liver to produce IGF-1. IGF-1 is the messenger that then goes out and actually does a large part of the job. When people give growth hormone credit for recovery, for holding on to muscle, for tissue repair, and for how quickly the body bounces back, a big part of what is carrying that signal is IGF-1. Growth hormone has some direct effects of its own, so this is not one hormone doing everything, but IGF-1 is doing a lot of the heavy lifting people assume growth hormone handles by itself.

So the chain is simple. Deep sleep drives growth hormone pulses. Growth hormone tells the liver to make IGF-1. IGF-1 goes out and does the work. Break any link in that chain and the whole thing weakens.

Think of it in terms of two different jobs. Testosterone is largely a build signal. It tells your body to put tissue on. IGF-1 is a big part of the repair and preservation side. It is involved in fixing what gets broken down and holding on to what you have already built. You want both working. Building without repairing, or repairing without a strong build signal, leaves you with half a system.

And here is the part that ties them together. Research suggests IGF-1 declines with age in much the same way testosterone does. The growth hormone pulses that drive it tend to get weaker and less frequent with each passing year, and that slide is well underway by 40. So the two hormones are not competing explanations for how you feel. They are often declining side by side, at the same time, and the effects compound on each other.

This is a large part of why some men start testosterone, feel better for a while, and then still feel like something is missing. They corrected one signal and left the other one sitting exactly where it was.

This is the single most useful thing on this page. IGF-1 can be measured. It is a straightforward blood marker, the same category of test as the bloodwork you would already run to check testosterone. It is not exotic and it is not hard to order. And yet most men over 40 have had their testosterone checked at least once and have never had IGF-1 measured a single time.

Sit with that for a second. If you are making decisions about your body, your training, and possibly your hormones based only on a testosterone number, you are working with half of the information available to you. The other half has been sitting there the whole time, testable, and simply never got looked at, mostly because no one told these men it existed or that it mattered.

Before anyone runs off thinking the goal is to drive this number as high as possible, this is where this stays a research resource and not a hype machine. More IGF-1 is not automatically better. IGF-1 is a growth signal, and the same signal that helps repair tissue is, by its nature, a signal that tells cells to grow and divide. Research suggests that pushing IGF-1 chronically high, well above the normal range, carries its own set of concerns rather than simply being an upgrade. The goal is not the ceiling. The goal is a normal, healthy range for your age.

The entire reason to care about this is not to max out a number. It is to avoid being quietly low in something you never knew you were supposed to check. That is a very different objective, and a much safer one. And the only way to know where you actually stand, low, normal, or fine, is to test it rather than guess.

If a test comes back low, start with the things that move IGF-1 for free, because those same things are what make everything else in your body work better anyway. This is the foundation, and for a lot of men it is enough on its own.

Deep sleep

This is the big one. Growth hormone is released in pulses during your deepest stage of sleep, and those pulses are what drive IGF-1. Short sleep or broken sleep means weaker pulses, and weaker pulses mean less IGF-1. This is not a minor effect at the edges. For a lot of men over 40, fixing sleep is the single highest return change available, and it costs nothing.

Resistance training

Lifting hard enough to genuinely challenge the muscle triggers a natural growth hormone response in a way that light or casual movement does not. Training here is not just about burning calories. It is a direct signal that supports the exact hormone we are talking about. Research suggests the intensity matters, meaning the effort has to be real rather than going through the motions.

Protein

Your body cannot produce IGF-1 well if it does not have the raw material to build it from. Research suggests adequate protein intake supports IGF-1 production, and most men who are struggling with recovery and muscle turn out to be eating less protein than they think they are. This is one of the most common quiet gaps, and it is fixable at the grocery store.

Body fat

Carrying excess body fat, especially visceral fat, which is the fat packed around your organs rather than under your skin, appears to work against IGF-1 production. Bringing that down tends to support the system rather than fight it, which is another reason the basics stack together instead of competing.

For the research audience specifically, there is a layer beyond lifestyle, and this is where the compounds people study come in. Everything in this section is mechanism and education only. There are no doses here, no protocols, and no sourcing, because that is not the point and it is not what this is for. The point is to understand how each of these actually relates to IGF-1, and to see the one idea that ties them together.

That idea is a ladder of directness. Each option is a more direct way of affecting IGF-1 than the one before it, and the more direct the method, the more caution it demands, not less.

Growth hormone secretagogues

A secretagogue is simply a compound that signals your own body to release more of something it already makes. In this case, the something is your own growth hormone. This is the least direct approach and where most researchers look first. The combination that comes up most often is CJC-1295 paired with Ipamorelin. CJC-1295 is a growth hormone releasing hormone analog, which in plain terms means it mimics the natural signal that tells your pituitary, a small gland at the base of your brain, to release growth hormone. Ipamorelin works through a second, different pathway to also prompt a release. They get paired because they push two separate levers at once, so your own growth hormone pulses come out stronger and your liver does the rest.

Tesamorelin, often also paired with Ipamorelin, is worth noting for one reason. It is the one compound in this group with an actual approved medical use, approved specifically to reduce visceral fat, the fat around the organs, in a particular patient population. That is why it comes up so often in conversations about belly fat that will not move, and it means it has been through more formal study than most of the others here. The key thing about every secretagogue is that because they ask your own body to release its own growth hormone, your natural regulation is still in the loop. That built-in limit is what makes this the gentler end.

Exogenous HGH

This is the middle rung, and the one skipped most often, even though it is the most common way people actually raise growth hormone. Exogenous simply means from outside the body. Exogenous HGH is growth hormone itself, the same molecule your body already makes, given directly rather than signaled for. Instead of nudging your own pulses, you are adding growth hormone straight into the system, and your liver responds by producing more IGF-1. Research suggests this is the exact reason IGF-1 is the standard blood marker doctors use to monitor anyone on growth hormone. They are not tracking the growth hormone hour by hour. They are tracking what it produces, which is IGF-1, and they use that number to keep it inside a safe range.

That directness is also what moves it up the caution ladder. When you work through your own pulses with a secretagogue, your body still applies some natural brakes. When you supply the hormone directly, most of those brakes are gone, and it becomes far easier to push growth hormone, and therefore IGF-1, past the normal range and into the territory we already covered, where more is not better. There is also a hard reality worth stating plainly. Exogenous HGH is a prescription medication. Its approved uses are for specific medical conditions, and using it outside of those, for body composition, anti aging, or performance, is not an approved use, is specifically restricted under federal law, and carries real health risk when it pushes the system past a normal range. That is not here to scare anyone. It is here because you cannot understand IGF-1 honestly without knowing this is the most direct route to raising growth hormone, and the more direct the route, the more it has to be treated with respect.

IGF-1 LR3

This is the top of the ladder. At the far end there is IGF-1 itself, in a research form usually referred to as IGF-1 LR3. The LR3 part refers to a modification that makes it stay active in the body longer than the natural version does. This is the most direct option there is, because you are skipping every step in between and supplying the finished messenger rather than signaling your body to produce it. It is also the one researchers approach with the most caution and the least casual attitude, for good reason. It is the furthest thing from a lifestyle change on this entire list. Research suggests it is the most powerful lever here and also one of the least fully understood over the long term, which is a combination that calls for more care, not less. It is a research chemical and not an approved medication for human use.

There is an entire shelf of products sold specifically on the claim that they raise IGF-1, and most of them do nothing at all. The most common version is oral IGF-1, sold as a pill or a spray you swallow. Here is the problem, and it is basic biology. IGF-1 is a protein. When you swallow a protein, your digestion breaks it apart into smaller pieces before it ever reaches your blood. An oral IGF-1 product gets taken apart in your stomach into fragments your body cannot use as IGF-1. It does not arrive intact, which means it cannot do the thing the label is promising.

The simple rule to carry with you is this. If a product promises to raise a hormone like IGF-1 and it is something you swallow, the burden of proof is on the seller to show that it actually reaches your blood intact. Almost none of them can show that, because for a protein taken by mouth it usually is not happening. Save the money. The things that genuinely move IGF-1 are the sleep, the training, the protein, and the body fat, and for the research audience, studied compounds. Not a nine dollar spray or a bottle of capsules with a big promise on the front.

This article is for educational and research purposes only. It is not medical advice. Nothing here is a suggestion to use any compound. Speak with a qualified medical professional about your own health and any bloodwork or treatment decisions.