Hormones are essential for normal and development. It enables youths to achieve normal height, and adults to burn fat (lipolysis), regulate insulin and glucose, and synthesize protein. Hormones also helps support sex and thyroid function.1
A moderate-sized peptide secreted in pulses throughout the day, G H is the most abundant of the pituitary hormones.1 Lipolysis, or fat burning, is a unique function of G H that results in increased circulating levels of free fatty acids and ketone bodies.
G H peaks in puberty and starts to decline in early adulthood. It has been estimated that secretion of G H declines by approximately 14% for every decade after entering adulthood.2
The decreased G H associated with aging is thought to contribute to the following physiologic changes:
Clinically, restoring G H to adequate levels has been shown to decrease visceral fat volume.4 improve mood, and increase muscle.5
Because low hormone levels have been linked to many symptoms of aging, interest in hormones has intensified particularly as the proportion of seniors in Canada increases. Conditions such as fibromyalgia, metabolic syndrome and cardiovascular disease have also been linked to low G H. Consequently, early identification and correction of sub-optimal GH levels may help reduce symptom severity or limit disease progression. Various lifestyle and dietary changes have been shown to improve endogenous GH secretion.
Why Test Urine?
Hormones are released from the anterior pituitary approximately every 2 hours throughout
the day.6 Given the cyclic nature of G H release, neither single nor multiple serum
collections can reliably capture peak hormone levels. Nearly half of daily G H output is secreted overnight during the onset of slow wave (non-REM) sleep. Thus, an overnight or 24-hour urine collection measures the cumulative total of all the G H produced during the collection period. In men, the overnight surge is the dominant source of G H.7 In addition to their overnight surge, women tend to have higher pulse amplitude throughout the day, making their overall G H levels higher than those of men.
Research shows that urine G H levels correlate with circulating (serum) G H levels, both in the rested state and after exercise.8.9 G H is freely filtered out of the blood; however, since most is reabsorbed in the kidneys, urine G H is only 0.025% of what is in serum. This is the first test in Canada to utilize new technology that enables highly accurate measurement of the low levels of G H found in urine.
This urine G H assay is not validated to diagnose G H deficiency in either children or adults. Specimens received from patients under 18 years of age will not be processed.
This assay is not validated to monitor the effectiveness of injectable G H therapy.
Urine hormone testing is not appropriate for patients with impaired renal function or those on diuretic medication.
Gender-stratified references ranges were developed using results from a cohort of clinically normal men and women aged 18 years and older. Gender stratification and creatinine normalization are essential to clinically relevant results.
G H receptors are present in many tissues, which means it can affect a variety of physiological systems including:
Optimal levels of GH may help increase resting energy expenditure (REE) independent of changes in lean body mass.4
Sub-optimal GH may contribute to metabolic syndrome and weight gain via the following:
The lipolytic effects of GH may be attenuated in women, elderly and in the presence of abdominal obesity.4
hormone deficiency has been linked with:
Insufficency of GH is associated with increased rish for thrombosis and atherosclerosis due to increased levels of of plasminogen activator inhibitor-I (PAI-I).5 Other cardiovascular risk factors including LDL cholesterol, total cholesterol and diastolic blood pressure all tend to improve when hormone deficient adults are given GH.
Sub-Optimal or Deficient?
Although many of the physiologic changes associated with aging are also linked to low levels of hormone, it is important to differentiate between age-related low hormone and Adult Hormone Deficiency (AGHD). Patient history consistent with probable AGHD is an indication for diagnostic testing and/or an endocrinological consult. Possible causes of adult-onset GHD include: history of brain injury or infection, auto-immune disease, radiation therapy or pituitary tumor. The insulin tolerance test is commonly used to diagnose GHD in Canada, although the arginine and GHRH stimulation test has fewer false positives.11 Diagnosed hormone deficiency requires administration of exogenous hormone (somatomedin).
An age-related decline in GH typically results in sub-optimal rather than clinically low GH levels. Other factors that negatively impact GH include: obesity, sex steroid hormone imbalances, excessive alcohol intake, refined carbohydrates and sleep apnea. fortunately, there are a number of lifestyle factors that positively impact GH secretion including: intermittent fasting, increased body temperature, exercise, and restful sleep.
IGF-I Versus Hormone
As illustrated in Figure 1, liver synthesis and secretion of IGF-I is dependent on GH. In circulation, IGF-I is bound to one of six IGF binding
proteins, which prolong its half-life and provide more consistent levels throughout the day. Consequently, many clinicians use total IGF-I as a surrogate marker for hormone. Most often, total IGF-I (free IGF-I + IGFBP3) is measured, however the secretion of IGF binding protein can vary independent of hormone. The following are examples of when IGF-I and hormone levels do not correlate well: