just wondering. what causes a deficiency in some people. especially older people who take exogenous amounts for HRT
So, I'll cover GHD in depth before I answer the HRT part because to understand why GH is prescribed can sometimes answer the question.
GHD or growth hormone deficiency is usually detected early in life due to the outstanding work of pediatricians and the monitoring of height. We have all heard the story's of people who weren't growing at the expected rate and they were given gh to help due to GHD. That's a pretty common use of it. However...ghd can either develop later in life as well, or can develop due to another medical condition. For example that would explain hrt and gh use: Jim had testicular cancer. Jim went through radiation. Jim had one or both of his testicles removed. Jim now needs HRT for the low testosterone from havinvg his nads snipped. The radiation also flipped a gene on/ or off. Now jim has low gh because of genetic issues brought on by the chemo/radiation. Jim also now needs GH.
Causes may include genetics, trauma, infections, tumors, or interactions with certain genes.
That stuff happens more than you think. Also Hypopituitarism is a thing. This will often require at least thyroid medication as well as gh and sometimes TRT. It's completely plausible that someone as young as 20 could suffer from Hypopituitarism. They get this from an endo.
More likely than those however is the fact that some get their HRT from an anti aging clinic. Some of these clinics are progressive and offer hgh to those over 35. Some endos are also offering hgh and peptides now as an additional service they can offer with the promise of better sleep, more muscle and less bodyfat.
People who take test often don't have problems with gh, igf1 or ect if they live a active, healthy lifestyle including regulation of sleep.
People who don't sleep for 5 to 8 hrs / night for at least 4x a week can show signs of lower gh but normal igf1. Maybe even higher than normal when on HRT. Also remember gh decreases as you age as well.
I'm unaware of low gh levels without a medical condition unless you're sleeping like an ahole.