A low IGF-1 level means your body is producing less of a key growth-promoting hormone than expected for your age. IGF-1 (insulin-like growth factor 1) is the main hormone your liver releases in response to growth hormone, and it drives tissue repair, bone strength, and muscle maintenance throughout life. A result below your age-specific reference range can point to a problem with growth hormone production, liver function, or nutrition, though the meaning depends heavily on context.
How Your Body Makes IGF-1
Your pituitary gland, a pea-sized structure at the base of your brain, releases growth hormone in pulses throughout the day. Growth hormone travels to the liver, where it triggers the production of IGF-1. The liver then releases IGF-1 into the bloodstream, where it acts on tissues throughout the body to promote cell growth, repair, and metabolism. This relay system means a low IGF-1 reading could reflect a problem at either end: too little growth hormone coming from the pituitary, or a liver that can’t respond to the signal properly.
What Counts as Low
IGF-1 levels are always interpreted relative to your age because they shift dramatically over your lifetime. They peak during puberty and early adulthood, then steadily decline. For a healthy adult between 21 and 25, the typical range runs from roughly 158 to 416 ng/mL (5th to 95th percentile). By ages 46 to 50, that window drops to about 73 to 235 ng/mL. And by 76 to 80, normal values fall between roughly 62 and 211 ng/mL.
A result that looks alarming at age 25 might be perfectly normal at age 70. This is why your lab report should include an age-adjusted reference range. If your level falls below the lower end of that range, your doctor will typically want to investigate further.
Common Causes of Low IGF-1
Growth Hormone Deficiency
The most straightforward explanation is that your pituitary gland isn’t making enough growth hormone to stimulate normal IGF-1 production. This can be congenital (present from birth) or acquired later in life from pituitary tumors, head injuries, radiation therapy, or surgery near the pituitary. In children, growth hormone deficiency shows up as noticeably slow growth. Height falls below the third percentile, and growth velocity drops below 6 cm per year before age 4 or below 5 cm per year between ages 4 and 8. Bone maturation typically lags more than two years behind the child’s actual age.
In adults, the picture is subtler. Low IGF-1 from growth hormone deficiency tends to cause increased body fat (especially around the midsection), reduced muscle mass, low energy, decreased bone density, and sometimes impaired concentration or mood changes. One important caveat: 30 to 40% of adults with confirmed severe growth hormone deficiency still have IGF-1 levels that fall within the low-normal range. So a “normal” result doesn’t always rule out the problem, and a low result doesn’t confirm it on its own.
Liver Disease
Since the liver is where IGF-1 is actually manufactured, liver damage can directly suppress production. Cirrhosis has been recognized as a cause of IGF-1 deficiency since the late 1980s, with levels dropping noticeably even in early-stage disease. The decline happens for two reasons: cirrhotic livers have fewer growth hormone receptors, so they respond poorly to the pituitary’s signals, and the progressive loss of functional liver tissue reduces the organ’s overall ability to synthesize the hormone.
Poor Nutrition and Low Protein Intake
Your diet has a surprisingly strong effect on IGF-1. Protein restriction alone can lower IGF-1 by about 30%, independent of total calorie intake. Research published in Cell Metabolism found that people eating a low-protein diet had IGF-1 levels roughly 30% lower than those eating high-protein diets, a difference that held up across multiple dietary interventions. Severe caloric restriction produces similar effects. This means that malnutrition, eating disorders, or even prolonged very-low-protein diets can push IGF-1 below normal.
Normal Aging
Circulating growth hormone and IGF-1 both peak around puberty and early adulthood, then progressively decline with each decade. This natural drop is sometimes called “somatopause.” It’s a normal part of aging, not a disease, though it does contribute to age-related changes in body composition, bone density, and cardiovascular health.
Genetic Conditions
Laron syndrome is a rare inherited condition where the body produces plenty of growth hormone but the receptors for it don’t work properly. People with Laron syndrome have high growth hormone levels but very low IGF-1, resulting in significant short stature. It was first described in 1966 and remains the best-characterized genetic form of IGF-1 deficiency.
Effects on Bone Health
One of the most well-documented consequences of persistently low IGF-1 is reduced bone strength. A large study of older men in Sweden (the MrOS study) found that each standard-deviation decrease in IGF-1 was associated with a 23% higher risk of any fracture, a 45% higher risk of hip fracture, and a 40% higher risk of vertebral fracture. The researchers estimated that low IGF-1 accounted for nearly 23% of hip fractures in that population. The connection works partly through bone mineral density: low IGF-1 leads to thinner, weaker bones over time.
How Low IGF-1 Is Investigated
A single low IGF-1 reading is a screening clue, not a diagnosis. Your doctor will first consider whether something obvious could explain it, like liver disease, malnutrition, or a medication you’re taking. Metformin, commonly prescribed for diabetes, may lower IGF-1, particularly in children during the first few months of use, though its long-term effect in adults is less clear.
If growth hormone deficiency is suspected, the next step is typically a stimulation test. Because growth hormone is released in bursts and fluctuates throughout the day, a random blood draw for growth hormone isn’t reliable. Stimulation tests use specific triggers to provoke a growth hormone response, and the peak level your body reaches helps confirm or rule out a deficiency. In children, low IGF-1 levels are interpreted relative to bone age rather than calendar age, since delayed skeletal maturation can shift what counts as normal.
Treatment for Confirmed Deficiency
When low IGF-1 is traced back to genuine growth hormone deficiency, the standard treatment is daily injections of synthetic growth hormone. This therapy was first approved in 1985 for children with growth hormone deficiency and has since been expanded to eight approved pediatric uses, including Prader-Willi syndrome, Turner syndrome, and children born small for gestational age who don’t catch up on their own. Most children with Prader-Willi syndrome have low IGF-1, and 40 to 100% meet formal criteria for growth hormone deficiency.
In adults, growth hormone replacement aims to normalize body composition, improve bone density, and restore energy levels. Treatment is monitored by tracking IGF-1 levels over time, adjusting the dose to bring IGF-1 into the middle of the normal range for your age. When low IGF-1 stems from liver disease or nutritional deficiency, treating the underlying cause is the priority. Restoring healthy liver function, for example, brings IGF-1 levels back toward normal without hormone replacement.
What a Low Result Means for You
If your lab work shows low IGF-1, the result tells you something is limiting your body’s production of this hormone, but it doesn’t tell you why on its own. The cause matters enormously. A 30-year-old with an IGF-1 of 90 ng/mL and a history of a pituitary tumor is in a very different situation than a 70-year-old with the same number and no other symptoms. Context, including your age, symptoms, medical history, nutritional status, and liver health, determines whether a low reading is a red flag that needs urgent follow-up or an expected finding that simply needs monitoring.