The insulin-like growth factor 1 (IGF-1) is the main mediator of the human growth hormone (HGH). More specifically, IGF-1 mediates its anabolic effects such as growth, development, and recovery in each of your tissues.
Together, the two hormones form the so-called GH/IGF-1 axis which plays a major role at every age.
It stimulates the growth of children as the levels of HGH and IGF-1 slowly increase during childhood and reach a peak during puberty, coinciding with the pubertal growth spurt.
Then, IGF-1 levels slowly decline throughout adulthood, but your body continues to produce it under the stimulus of HGH as you need it for recovery, preserving bone mass, muscle mass, and tissue hypertrophy.
If your IGF-1 levels drop too low, it can lead to bone loss, slower recovery after injuries, muscle atrophy, and reduced performance.
On the other hand, an excess of IGF-1 can lead to acromegaly and shorter life expectancy. That’s why it is important to keep your IGF-1 levels balanced for optimal health and quality of life.
How to test IGF-1
A blood sample is the only reliable way to test your IGF-1 levels. Thus, you will have to visit a lab in person, where an experienced healthcare professional will draw a small amount of blood from the vein in your arm.
The whole process takes less than a few minutes as the professional will insert a small needle into your vein and collect the blood in a tube or a vial. You may feel a slight sting as the needle is inserted.
Make sure to warn the healthcare professional if you have a history of fainting during such procedures or if you have problems with your coagulation. Overall, there is very little risk in having a blood test – usually only mild bruising or pain that goes away quickly.
There is no need for any special preparation before the test, except for discontinuing any biotin supplements that you may be taking. Researchers warn that biotin supplementation may interfere with the standard immunoassays used for measuring various indicators including IGF-1.
In addition, there are also more accurate but much more expensive tests for measuring IGF-1 levels which involve using mass spectrometry.
A doctor will most likely assign you an IGF-1 test in order to determine if they suspect that you may have growth hormone deficiency (GHD).
That’s because circulating IGF-1 levels correspond to the mean HGH levels in the body. Yet, testing HGH directly is not quite informative because it can fluctuate a lot. On the other hand, IGF-1 levels are relatively stable throughout the day.
Keep in mind that the IGF-1 test has relatively low sensitivity and normal IGF-1 levels do not exclude GHD
Apart from GHD, an imbalance of your IGF-1 levels can be caused by growth hormone insensitivity (a congenital condition also known as Laron’s syndrome) or due to liver cirrhosis.
The liver is the main organ that releases IGF-1 in the blood under the stimulus of HGH, so if your liver is severely damaged, your IGF-1 levels will be low.
Normal IGF-1 levels by age
There is not a universal cut-off point for the normal IGF-1 levels in adults. Instead, there are different reference ranges for this hormone depending on the age.
Here are the optimal IGF-1 levels by age which are based on several studies in children, adolescents, and adults:
IGF-1 levels in girls/women (ng/mL)
IGF-1 levels in boys/men (ng/mL)
|Puberty (11-17)||335.2||716.6||Puberty (11-17)||359.4||850.1|
As you can see from the table, sex does not affect IGF-1 levels significantly. IGF-1 levels peak during puberty and then slowly decline throughout adulthood in both genders.
These age-related changes are in accordance with the HGH levels in the body. The peak in GH/IGF-1 levels also coincides with the rapid growth and development during puberty
Having adequate GH and IGF-1 levels during childhood and adolescence allows individuals to reach their final height.
Genetics, diet, physical activity, body weight, and body composition can influence IGF-1 levels in adults
Although growth is complete after the end of puberty, optimal IGF-1 continues to support several anabolic processes in adults including muscle hypertrophy, tissue growth and regeneration, and bone mineral density.
Apart from age, several other factors may also influence the levels of IGF-1 in adults. These include genetics, diet, physical activity, body weight, and body composition.
For example, different populations may have different average IGF-1 levels. According to one study, Caucasian people and African-American people had slightly higher IGF-1 levels compared to Mexican-American individuals.
Furthermore, your body weight and body composition can influence the IGF-1 levels in your body quite significantly. Studies show that obese individuals have about 35% lower IGF-1 levels compared to adults with normal BMI. Besides, losing as much as 30 kg of body weight resulted in a 40% increase in the IGF-1 levels in the obese individuals in the study.
People who practice fasting or restrict their protein intake may also have lower IGF-1 levels compared to the average individual. That’s because fasting and insufficient protein intake can lead to the release of a hormone called FGF21 which reduces the stimulus of HGH on IGF-1 synthesis.
How can low or high IGF-1 affect your life?
An IGF-1 imbalance can affect your life differently depending on your age. For example, low IGF-1 will have different effects in children compared to adults.
Children with IGF-1 deficiency experience stunted growth and short stature. Usually, the condition is due to growth hormone deficiency or growth hormone insensitivity.
If you are an adult with low IGF-1 levels, you may experience muscle wasting and atrophy, low bone mineral density, slower recovery from injuries, and an increased risk of bone fractures. If your condition is due to GHD, you may also experience reduced energy levels, body fat gain, and an increased risk of cardiovascular diseases.
On the other hand, if your IGF-1 levels are higher than the normal reference range for your age, this may indicate excessive production of HGH. The growth hormone excess is almost always caused by a pituitary tumor.
In children, GH/IGF-1 excess is extremely rare and can lead to a condition called gigantism, which manifests with excessive growth and body height that is way above average. The patients are tall with long limbs and elongated torsos.
In adults, GH/IGF-1 excess leads to the development of acromegaly. The condition does not affect the height of the patients, but it causes increased bone and cartilage thickness. This leads to facial and skeletal changes such as
- enlarged nose, lips, and tongue
- jutting out brows and lower jaw
- wider feet, hands, and fingers
Patients with GH/IGF-1 excess also tend to develop high blood pressure, arthritis, insulin resistance and have a shorter life expectancy.
What to do with IGF-1 imbalance?
The management of an IGF-1 imbalance depends on its main cause. If you have low IGF-1 levels, then the most likely cause for your condition is GHD. In such cases, your doctor will assess your symptoms and assign you a provocation test such as an insulin tolerance test to confirm the diagnosis.
Patients with GHD can successfully manage all their symptoms by taking recombinant HGH injections daily.
If you have low IGF-1 levels due to Laron’s syndrome, then HGH therapy would be ineffective. Instead, the treatment involves the use of recombinant IGF-1 and IGFBP3 – the protein that normally binds to the hormone. Similar to HGH, the medication is administered via subcutaneous injections.
If you are already healthy, then the best options to increase IGF-1 levels naturally include maintaining healthy body weight, avoiding fasting or protein restriction, and exercising regularly.
If you have abnormally high IGF-1 levels, then your doctor will also assign you an HGH test and an MRI to look for a hormone-secreting pituitary tumor. The condition can be managed by treating the tumor with surgery, radiation, or medications.
Unfortunately, the treatment is often followed by the development of hypopituitarism and the patients may require HGH therapy to manage the symptoms of GHD.