IGF-1: what is it?

Insulin-like Growth Factor 1 is what we mean when we talk about IGF-1.

It is a chemical communication that is carried through the circulation called a hormone, and it is responsible for stimulating the development of bone, muscle, and other tissues in the body.

As a result, we may classify IGF-1 as an anabolic hormone since it stimulates metabolic events that lead to the formation of new tissue.

After exercise, IGF-1 is created by our liver as well as our muscles, where it induces hypertrophy. Hypertrophy is defined as an increase in muscle volume or mass that results from a rise in the cross-sectional area of individual muscle fibres.

Therefore, IGF-1 activity is necessary for the process of increasing muscle mass and enhancing overall body composition.

IGF-1 has a role in ageing, which is defined as the gradual loss in the biological function of cells over time. It does this by encouraging cell growth and division.

IGF-1 also affects the way our bodies respond to insulin, both in terms of their function and their sensitivity. As a result, it plays a part in the control of the metabolic processes involving sugar and fat.

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How exactly is IGF-1 manufactured?

The axis of growth hormone and insulin-like growth factor-1
Our liver is responsible for the secretion of around 75 percent of IGF-1 in reaction to another hormone known as growth hormone (GH).

As its name implies, growth hormone is a hormone that encourages the expansion and maturation of cells, particularly throughout infancy. In adults, it has an effect on the metabolism of sugar and fat, as well as on the control of muscle mass, and it plays a function in the process of regulating muscle mass. The pituitary gland, which sits at the base of our brain, is responsible for secreting the hormone known as growth hormone.

The pituitary gland is capable of secreting growth hormone in response to a variety of stimuli, including physical activity, sleep, and dietary consumption. Once it has been secreted, growth hormone enters the circulation and operates on the liver, where it causes certain liver cells, known as hepatocytes, to create IGF-1 in response to the hormone’s presence.

The IGF-1 that is created by the liver will eventually end up in our circulation, where it will have the opportunity to act on a variety of different target tissues. As a result of this, it is referred to as circulating IGF-1 (cIGF-1).

IGF-1 is attached to one of six specialised proteins that are collectively referred to as IGF binding proteins. This prevents it from circulating freely in the circulation (IGFBPs). IGFBP3 stands out as the most significant transporter of IGF-1 among these four candidates.

IGF-1 is produced in muscle tissue.

The majority of the body’s other tissues, in addition to the liver, are also responsible for the creation of IGF-1. This includes the tissue found in muscles. IGF-1 that is produced by muscle cells and then released works locally on the same (also known as “auto”) or neighbouring (also known as “para”) muscle tissue rather than circulating broadly in the circulation. IGF-1 can be thought of as either an autocrine or a paracrine growth factor, depending on how you look at it.

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IGF-1 and the development of muscle

IGF-1 has a role in stimulating the process of hypertrophy, which refers to an increase in the mass and volume of muscle.

As was discussed in the blog post titled “Protein Synthesis and Hypertrophy (mTOR),” hypertrophy develops when the pace at which muscles produce new proteins exceeds the rate at which they degrade existing proteins. Using terminology that is more common in the scientific community, we may state that hypertrophy is the result of the rate of strength training (MPS) being greater than the rate of muscle protein breakdown (MPB).

IGF-1 helps to enhance increases in muscle mass by acting both to stimulate the synthesis of muscle protein and to prevent the breakdown of muscle protein at the same time.

In a similar vein, IGF-1 is responsible for the activation of specialised muscle cells known as satellite cells. Satellite cells are a special kind of stem cell that have the potential to develop into a wide variety of specialised muscle cells. Satellite cells, in response to IGF-1, will fusion with muscle fibres and lay down new myofibrils. Myofibrils are the thread-like components of the muscle that are responsible for contraction. You may remember from the blog post titled “Protein Synthesis and Hypertrophy (mTOR)” that the process of gaining strength, which is referred to as “myofibrillar hypertrophy,” involves the synthesis of new myofibrils.

People who have greater amounts of IGF-1 circulating in their bodies may find it easier to acquire muscle and strength (as measured by a muscle’s maximum force output). This is because IGF-1 plays a function in the formation of muscular tissue.

How exactly does IGF-1 increase the production of muscle protein?

IGF-1 is able to have its effects felt throughout the body because it binds to a specific receptor known as the IGF-1 receptor (IGF-1R).

When insulin growth factor 1 attaches to its receptor, insulin growth factor 1 receptor (IGF-1R), it sets off cascades of chemical processes that we refer to as signalling pathways. The PI3K/AKT pathway is known to be one of the most important signalling pathways that may be activated by the IGF-1R. Exercise, as a side note, is another thing that can directly activate this pathway.

The IGF-1R is responsible for activating the PI3K/AKT pathway, which, in turn, promotes molecules that turn on the creation of proteins. One of these molecules is called mTOR, and we looked at it in depth over at the blog entitled Protein Synthesis and Hypertrophy (mTOR).

The PI3/AKT pathway not only encourages the manufacture of new proteins, but it also suppresses molecules (such as FoxO-1) that are in charge of the catabolism, which is the process of breaking down proteins into their constituent parts.

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IGF-1 and the ageing process

It is believed that IGF-1 plays a function in both the process of cell division and the process of cell death, both of which are essential components of the ageing process.

Lower circulating levels of IGF-1 have been demonstrated to be connected to slower ageing and a longer lifespan in animal experiments on several occasions.

The image, however, is somewhat more difficult when applied to humans, since study findings have been shown to be inconsistent. According to the findings of a few research including healthy centenarians (defined as individuals who are 100 years old or more), these individuals do in fact have comparatively lower levels of IGF-1 in their circulation.

In addition, it has been suggested that fasting and caloric restriction (that is, limiting the quantity of calories you eat), both of which have been demonstrated to delay the ageing process of cells and increase longevity, may also reduce the amount of IGF-1 that is circulating in people.

Both of these lines of evidence point to the conclusion that having lower circulating levels of IGF-1 is associated with having a slower rate of ageing. On the other hand, increased levels of IGF-1 in circulation have been linked to accelerated ageing.

One theory that might explain the connection between the two is that lower levels of IGF-1 are associated with increased insulin sensitivity (explained in the following section). The inability to respond properly to insulin can, in turn, result in inflammation and damage to cells, three factors that hasten the ageing process.

When we take into account the fact that high levels of IGF-1 also increase muscle growth, we might conceive of the process of ageing as a possible drawback to improved muscle growth. This trade-off was also true of having greater mTOR activity, as you may have discovered with your mTOR trait.

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The insulin-like growth factor 1 and its sensitivity

IGF-1, also known as insulin-like growth factor 1, gets its name from the fact that its molecular structure is very similar to that of insulin. Insulin is the hormone that enables cells to take up sugar (glucose) from the bloodstream and utilise it.

The levels of glucose in the blood begin to rise when the tissues in our bodies become less responsive or sensitive to the hormone insulin. When glucose levels in the blood remain high for an extended length of time, this can lead to inflammation as well as damage to cells and organs.

According to studies, IGF-1 may be able to increase the sensitivity of our tissues to insulin.

IGF-1 and insulin are both capable of binding to a specialised “hybrid” receptor that is known as the IGF-1/insulin hybrid receptor. When this hybrid receptor is active, it encourages tissues, especially skeletal muscle, to take up glucose from the blood stream. Skeletal muscle is particularly affected by this stimulation.

Despite the fact that this impact exists, the connection between the circulating levels of IGF-1 and insulin sensitivity continues to be highly convoluted. This is due in part to the fact that IGF-1 can also inhibit the release of growth hormone, which in turn affects how insulin works in the body. Clinical investigations have shown that reduced insulin sensitivity can be the result of either low or high levels of the growth factor IGF-1.

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Genetics

Your most recent characteristic analyses variations in your IGF1 gene (which is responsible for encoding the IGF-1 hormone) as well as you IGFBP3 genes (which encodes the IGFBP3 protein).

These gene variants have an effect on the amount of circulating IGF-1 in your body. In turn, this affects your tendency for muscular growth and the rate at which you age, in addition to the sensitivity of your insulin receptors.

Be sure to check out your Insights and Actions to determine which alterations to your food, supplement regimen, exercise routine, and lifestyle choices will help you achieve your desired IGF-1 levels.

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