GH stimulates approximately 80% of circulating insulin-growth factor-I (IGF-1) in the liver, making it a main source of circulating IGF-1. In addition, recent clinical and other studies have clarified that the liver is also an important target organ of growth hormone (GH) and IGF-1, and growth hormone deficiency (GHD) is associated with nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH), which are significant complications of adult GHD [1].

Adult GHD is an established clinical entity defined by a defect in GH secretion in adult associated with central obesity, loss of muscle mass, decreased bone mass, increased prevalence of NAFLD [2], and impaired quality of life [3], [4]. Fat mass is increased, as are levels of cholesterol, low-density lipoproteins, triglycerides, and apolipoprotein B, and lean body mass is decreased. It is also associated with glucose intolerance, probably aggravated by central obesity that closely resembles metabolic syndrome. Importantly, life expectancy is reduced in patients with hypopituitarism with underlying GHD due to an increased risk of cardiovascular disease. Adult GHD may be caused by structural insults, such as an intrasellar mass, inflammation, autoimmunity, or local vascular compromise resulting from surgery, radiation therapy, or head trauma [5], [6]. Survivors of childhood cancers are also at risk, especially if they have received radiation therapy. The symptoms in adult GHD are usually nonspecific, and GH replacement therapy is approved only for patients with true GHD; therefore, precise diagnosis is necessary. Although serum IGF-1 level is a useful marker of endogenous GH secretion and decreased IGF-1 levels as adjusted for age and sex suggest GHD, a GH provocation test is essential for the diagnosis [5]. It is important to note that non-adult growth hormone deficiency (GHD) patients who are obese with NAFLD can also have low GH and IGF-1 levels with a blunted response to GH provocation test; therefore, these individuals should not be misdiagnosed as adult GHD and GH replacement should not be offered [7].