Insulin-like growth factor 1 (IGF-1), also called insulin growth factor 1, is a hormone produced in the liver in response to receiving signals of growth hormone (GH) sent from the anterior pituitary gland. GH stimulation is the primary source of IGF-1 production. 

Stimulating IGF-1 production is only one aspect of the many functions of GH in the body. IGF-1 plays a mediating role in some growth hormone functions, including cellular regeneration. These hormones form part of the somatropic axis, which aids in development, growth, puberty, and reproduction. 

IGF-1 is an insulin-related peptide consisting of 70 amino acids. While the liver is the primary producer of insulin growth factor 1, a lesser amount comes from other tissues, such as skeletal muscle and cartilaginous cells, where it acts locally, functioning as a paracrine hormone.  

While a primary function of IGF-1 is stimulating cell growth, insulin growth factor 1 also aids in lipid and glucose metabolism. A primary difference between growth hormone and IGF-1 is that GH levels vary considerably during the day, as it releases every few hours in pulsatile bursts and rapidly leaves the bloodstream. IGF-1 levels remain stable, although the amount depends on GH excess or deficiency. Insulin growth factor 1 testing is useful in determining growth hormone deficiency in adults. 

How Do IGF-1 and GH Work?

IGF-1 and growth hormone are part of the GH/IGF axis, a feedback loop involving the hypothalamus, pituitary gland, and liver. The hypothalamus measures the amount of insulin growth factor 1 in the bloodstream to determine if more is necessary. If so, it secretes growth hormone-releasing hormone (GHRH), which travels to the anterior pituitary gland to stimulate the somatotrophs (GH-producing cells) to release somatotropin (GH) into the bloodstream. 

Upon release, GH travels throughout the body and brain, delivering signals to GH receptor cells to stimulate their functions. As growth hormone enters the liver, its signals stimulate the release of IGF-1 into the bloodstream. GH rapidly enters the bloodstream from the pituitary gland in pulsatile bursts, racing to its receptors to deliver the signal before leaving the bloodstream. 

Insulin growth factors support cell proliferation and function throughout the body, influencing regeneration and repair in tissues, muscles, bones, skin, and organs. IGF-1 mediates the effects of GH on these areas, as well as throughout the brain, to support healthy brain functions. 

IGF-1 and GH also help the body maintain insulin and blood glucose balance. IGF-1 deficiency and GHD are often linked to diabetes, which is why blood sugar and cholesterol levels are also checked when running hormone tests. 

GH and IGF-1 help promote sexual functions and fertility in men and women, stimulating spermatogenesis in males and ovarian follicular functions in females. Checking IGF-1 levels may help men and women dealing with fertility issues.

Insulin growth factor 1 and growth hormone increase renal blood flow to support healthy kidney functions. Receptors for these cells can also be found throughout the cardiovascular system, supporting healthy heart functions, including nitric oxide release. IGF-1 and growth hormone help support thymus function and white blood cell production for the immune system. 

Symptoms of IGF-1 Deficiency

Age plays a role in the symptoms of insulin-like growth factor 1 deficiency. Impaired IGF-1 production affects children differently than adults, often showing up around puberty as the growth rate of their peers might exceed that of young people with growth hormone deficiency. 

IGF-1 deficiency symptoms often mimic those of growth hormone deficiency (GHD), with GHD often being the diagnosis for adults and children with low IGF-1 levels since growth hormone is the stimulator of insulin growth factor 1 production. With IGF-1 regulating the growth-promoting effects of GH on the body’s tissues, including the bones, growth plates, and muscles, it is not surprising that a child who is not keeping up with expected growth is diagnosed with a deficiency in these hormones. 

IGF-1 deficiency symptoms in children include:

  • Slowed or inhibited growth rate in early childhood or puberty
  • Delayed puberty
  • Shorter stature – below normal levels
  • Shorter arm and leg lengths
  • Tiredness or lack of energy
  • Delayed bone development
  • Thin hair or poor hair or nail growth
  • Younger appearance than their peers

IGF-1 and growth hormone deficiency show up differently in adults who are no longer concerned about reaching their “adult” height. While GHD has many symptoms, those generally associated with low insulin growth factor 1 levels are shown below:

  • Thinning hair
  • Poor nail growth
  • Loss of lean muscle
  • Reduced bone density
  • Fatigue
  • Decreased physical performance
  • High LDL and total cholesterol
  • Low HDL cholesterol
  • Depression 
  • Cognitive changes
  • Dry, thinning skin and wrinkles

Some Reasons for IGF-1 Deficiency

IGF-1 deficiency can occur for many reasons, with differences between children and adults. The most likely cause is declining growth hormone production, which occurs with age. 

Diagnosing IGF-1 deficiency and GHD in children differs from adults, and this article focuses on IGF-1 deficiency in adults. Speak with a pediatric endocrinologist if your child is struggling with short stature or poor growth.

Adults can have low insulin-like growth factor 1 levels for multiple reasons, including the following:

  • Anorexia nervosa
  • Inherited defects
  • Unresolved or continuing childhood GHD
  • Chronic kidney or liver diseases
  • Sex hormone deficiency 
  • Pituitary tumors or damage
  • Hypothalamic tumors or damage
  • Chemotherapy, radiation, or surgery to treat brain tumors
  • Inactive/ineffective forms of GH
  • Brain trauma
  • High doses of estrogen
  • Inflammation
  • Certain infections

Blood analysis can help rule out some of the causes of IGF-1 deficiency. An endocrinologist/hormone therapist is the best person to call when you have concerns about IGF-1 and growth hormone deficiency. 

How to Increase IGF-1 Naturally

Maintaining healthy IGF-1 levels is crucial for adult well-being and physiological functions. That means ensuring optimum growth hormone production to support insulin growth factor 1 release from the liver. 

Some of the many ways to increase IGF-1 naturally include:

  • Reduce abdominal fat – being overweight can decrease GH production
  • Reduce inflammation – lowering inflammation helps boost IGF-1 and GH levels – decrease consumption of inflammation-causing foods, including sugar, gluten, and dairy
  • Consuming adequate protein – not eating enough protein can lower IGF-1 levels, and high-protein diets can increase them – bone broth protein is an excellent source
  • Exercise – increasing physical activity helps support GH release from the pituitary gland – high-intensity interval training (HIIT) optimizes release
  • Vitamins and minerals – zinc, magnesium, vitamin C, selenium, vitamin D, and thiamine (B1) are levels to check to see if you are low in any of these – if so, supplement to help boost IGF-1 levels
  • Sleep – since most of the daily allotment of GH occurs during sleep, getting between 7 and 9 hours per night is crucial 
  • Reduce stress – increased or chronic stress causes high cortisol levels, which inhibit GH production and lower IGF-1 levels

Conclusion

IGF-1 deficiency can increase the risk of many health conditions, including cardiovascular disease, liver cirrhosis, type 2 diabetes, metabolic syndrome, neurodegenerative diseases (including dementia, Alzheimer’s disease, ALS, Parkinson’s disease, stroke), musculoskeletal disorders (including osteoporosis), renal disease, and more. 

Protecting growth hormone and insulin growth factor 1 levels is crucial as you age. Speaking with a hormone specialist to check these levels can help prevent more serious health issues from occurring. 

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