Growth Hormone (GH)

Growth hormone (GH), also known as somatotropin or human growth hormone (HGH), is a crucial peptide hormone produced by the anterior lobe of your pituitary gland [1]. This small, pea-sized endocrine gland located at the base of your brain serves as your body's hormone control center, releasing GH in short bursts or pulses throughout the day [1].

GH acts on many parts of the body to promote growth in children and maintain normal body structure and metabolism in adults [1]. The hormone's primary function is stimulating growth, cell reproduction, and regeneration, making it essential for normal childhood development and ongoing health throughout life [1].

The release of growth hormone is carefully regulated by your hypothalamus through two key hormones: growth hormone-releasing hormone (GHRH), which stimulates GH release, and somatostatin, which inhibits its release [1]. This sophisticated control system ensures GH is released when your body needs it most.

One of GH's most important functions is stimulating the liver to produce insulin-like growth factor-1 (IGF-1), which mediates many of growth hormone's growth-promoting effects [2]. This relationship between GH and IGF-1 is crucial for understanding how growth hormone works in the body. While GH levels fluctuate throughout the day, IGF-1 levels remain more stable, making it a reliable indicator of overall GH activity [2].

Interestingly, about 70% of daily GH secretion occurs during deep sleep phases, highlighting the critical connection between quality rest and hormone production [3]. This pulsatile release pattern means that random blood tests for GH can be challenging to interpret, which is why healthcare providers often rely on IGF-1 measurements instead.

Growth hormone levels are fundamental to both childhood development and lifelong health maintenance. In children, adequate GH levels are absolutely essential for normal growth and development [1]. Growth hormone deficiency in children leads to significantly shorter stature compared to peers, with affected children growing more slowly while maintaining normal body proportions [1].

Beyond childhood growth, GH continues to play vital roles throughout adult life. The hormone helps maintain normal body structure and metabolism, including keeping blood glucose levels within healthy ranges [1]. Adults with growth hormone deficiency often experience decreased bone density, reduced muscle mass, increased body fat, and fatigue [1].

GH's metabolic functions are equally important. The hormone helps regulate fat distribution, energy levels, and overall body composition [1]. It supports the maintenance of lean muscle mass and bone density, which become increasingly important as we age. This is why both deficiency and excess of growth hormone can lead to serious health consequences.

When GH levels are too low, individuals may face increased risk of cardiovascular disease, diabetes, and reduced quality of life [1]. Children with GH deficiency may also experience delayed puberty and other developmental issues beyond just short stature [1].

Conversely, excess growth hormone can be equally problematic. In children, too much GH causes gigantism, characterized by excessive height and enlarged hands and feet [2]. In adults, excess GH leads to acromegaly, causing enlarged facial features, hands, and feet, along with thicker bones [2]. Both conditions can result in serious health complications if left untreated.

The hormone also plays a role in cognitive function and mood regulation, with some studies suggesting that appropriate GH levels contribute to overall mental well-being and quality of life.

Measuring growth hormone presents unique challenges due to its pulsatile release pattern and short half-life in the bloodstream [1]. Unlike many other hormones that maintain relatively stable levels throughout the day, GH is released in short bursts, making random blood tests unreliable for assessing overall GH status [1].

The preferred method for evaluating growth hormone activity is measuring insulin-like growth factor-1 (IGF-1) levels [1]. Since IGF-1 levels remain more stable throughout the day and reflect the average GH activity over time, an IGF-1 test provides a much more reliable assessment of growth hormone function [1]. IGF-1 levels change predictably throughout life - they're normally low in early childhood, increase until they peak during puberty, then gradually decrease in adulthood [1].

When more detailed assessment is needed, healthcare providers may use growth hormone stimulation tests. These specialized tests involve administering substances like arginine, insulin, or growth hormone-releasing hormone (GHRH) to stimulate the pituitary gland's GH production [1]. By measuring how much GH the pituitary releases in response to these stimuli, doctors can assess whether the gland is functioning normally.

For suspected cases of excess growth hormone, such as in acromegaly or gigantism, doctors may use suppression tests. The oral glucose tolerance test is one such method, where glucose administration should normally suppress GH levels in healthy individuals [2]. If GH levels remain elevated despite glucose administration, it may indicate a growth hormone-producing tumor.

In research settings, 24-hour urine collection for GH measurement may be used, but this method is rarely employed in clinical practice due to its complexity and the availability of more practical alternatives [1]. The key is that any GH testing should be interpreted by healthcare professionals who understand the normal variations and can correlate results with clinical symptoms and other diagnostic information.

Understanding normal growth hormone and IGF-1 ranges requires recognizing that these levels vary significantly based on age, sex, and individual factors. Since direct GH measurement is challenging due to its pulsatile nature, IGF-1 levels serve as the primary indicator of growth hormone status [1].

For IGF-1 levels, there are distinct patterns throughout life. In infants under 11 months, normal ranges are 18-79 ng/mL for males and 14-106 ng/mL for females [2]. These levels gradually increase throughout childhood, reaching peak levels during adolescence. For example, at age 13, normal ranges are 101-620 ng/mL for males and 150-678 ng/mL for females [2].

Adult IGF-1 levels show a clear decline with age. Young adults aged 21-25 have normal ranges of 109-353 ng/mL for males and 101-347 ng/mL for females [2]. By ages 31-35, these ranges decrease to 95-290 ng/mL for males and 84-281 ng/mL for females [2]. This age-related decline continues throughout life, with adults aged 61-65 showing ranges of 64-240 ng/mL for males and 57-202 ng/mL for females [2].

For direct growth hormone measurements, normal adult levels typically remain below 5 ng/mL during random testing, while children can show ranges from 0-20 ng/mL depending on the timing of the test [1]. However, these direct measurements are less reliable due to the hormone's fluctuating nature.

It's important to note that reference ranges may vary between different laboratories and measurement methods [2]. Additionally, factors such as nutrition status, body composition, sleep quality, and overall health can influence these levels. Healthcare providers always interpret results within the context of clinical symptoms and individual patient factors.

The dramatic changes in IGF-1 levels throughout life highlight why age-appropriate reference ranges are crucial for accurate interpretation. What might be considered low for a teenager could be completely normal for an older adult, emphasizing the importance of professional medical interpretation of any hormone testing results.