Insulin Like Growth Factor 1 (IGF-1) Explained: Everything You Should Know
I wanted to take a few minutes to explain Insulin-Like Growth Factor 1 to you. This molecule is also called somatostatin C and more often IGF-1 for short. This hormone is widely discussed in the sports world for possible performance enhancement. It also shares the common name insulin with the medication used to treat type 1 diabetes. For these reasons, I thought it would be worth discussing and spending some time reviewing.
Anatomy, Physiology & Regulation
Briefly, I will discuss the anatomy, physiology and regulation of IGF-1. IGF-1 secretion is regulated by the release of human growth hormone, which is secreted from the pituitary gland. I have made a detailed video explaining growth hormone and I would encourage you to check that out if you want to know more. The function of IGF-1 and HGH overlap significantly and the distinction between the effects of HGH and IGF-1 are not entirely clear, and the research in this area is ongoing.
Human Growth Hormone Explained: https://www.youtube.com/watch?v=wdAKp1P_Z2w
IGF-1 is produced and secreted primarily from the liver, although other peripheral tissues, such as bone, produces its own IGF-1. The reason that insulin-like growth factor has the name is that it has an insulin like subunit that binds to insulin receptors, but only has 10% of the potency of regular insulin on glucose regulation.
Function & Effects
This is an anabolic hormone; in other words it ‘promotes growth’. While this includes skeletal muscle, it’s certainly not limited to it. It’s worth noting that it is not androgenic, as opposed to testosterone, meaning it doesn’t promote male sex characteristics such as facial hair and deeper voice.
It’s primary effect is growth stimulation. This is a balanced effect which affects all tissues equally, not just skeletal muscle. This occurs because it is released into the bloodstream by the liver, although local production by bones probably is a little more effective locally. Production peaks during puberty where whole body growth is at it’s greatest.
- Whole body protein synthesis and inhibition of protein breakdown (proteolysis)
- Enhanced bone mineralization
- Low blood sugar (hypoglycemia, remember it acts like insulin)
- Positive nitrogen balance
- Increased kidney filtration
- Partial reversal of catabolic activity of glucocorticoids on protein synthesis
- Diabetics: increased insulin sensitivity (not approved for this use)
Again, it’s function overlap with HGH significantly, so make sure to check out that video as well.
There is a rare medical condition where you either don’t produce insulin-like growth factor 1 or you are insensitive to it. Although there is an entire constellation of symptoms, the most prominent feature is short stature, hence the clinical title dwarfism. In folks who are responsive to it, but do not produce enough, there is a medication that can be used to treat them.
IGF-1 Supplementation and Athletic Performance
The internet is brimming with ‘experts’ and folks who have personal experience supplementing with IGF-1 who make wild claims about its anabolic benefits. This includes improved athletic performance, increased muscle strength and hypertrophy, and injury recovery.
There are no human trials of insulin like growth factor supplementation, only animals studies, and those are very limited. In humans, the only data we have is supplementation in folks who naturally do not produce enough. As a result, there is virtually no evidence to support an anabolic role for supraphysiological levels of systemic GH or IGF-I in skeletal muscle of healthy individuals. In other words, unless you have a deficiency, the evidence does not support supplementation.
Because they overlap, it’s worth pointing out that the evidence for HGH is not good either. For example, one study found supplementation of growth hormone is no more effective at skeletal muscle growth than a placebo.
- Low blood sugar (hypoglycemia)
- Retinal edema
- Bell’s palsy
- Severe muscle pain (myalgia)
Long term side effects are not well known primarily because of it’s very limited use as a medication and few clinical trials. It’s believed to share a side effect profile similar to HGH which includes:
- Enlarged heart (cardiomegaly)
- Muscle weakness (myasthenia)
- High cholesterol (hyperlipidemia)
- Impaired glucose regulation and increased risk of type I diabetes
- Increased fatigue
IGF-1 and Cancer
There is convincing experimental evidence that the HGH/IGF-1 axis plays an important role in cancer development and behavior. However to what degree, and in exactly what fashion, the results are mixed and unclear.
The working concept is that it may not necessarily cause cancer per se, but make tumors grow more quickly. This is based on the basic understanding that the hormonal axis is promotes growth of all tissues without discrimination.
As an example of evidence for cancer risk, folks with acromegaly or excessive HGH production as an adult are at increased risk of colorectal cancer.
Conversely, surveillance data on thousands of children and adults treated with HGH for deficiency have not shown an increase in cancer risk. I will also mention that because a lot of the children that have been treated with this relatively novel medication are still young adults, surveillance is ongoing and there is still much to learn.
Should you supplement?
If you haven’t figured it out, the simple answer is no and it’s illegal and an banned substance in professional sports. Supplementation should only be done under the supervision of a physician for specific medical reasons.
Because our understanding of it’s functions and side effects in folks with normal levels is so limited, the potential for harm and misuse is very high.
IGF-1 is a case of where the desire for performance enhancement greatly exceeds the science and understanding surrounding the hormone.
I will add that exercise and healthy sleep have been shown to boost HGH. This likely applies to IGF-1 as well.