How does human growth hormone (HGH) work?
Human growth hormone (HGH) is a key regulator of growth in our bodies, acting to build and maintain structures and tissues from our toes to our hair. As we age, not only do our reproductive functions decline, but growth also slows and eventually stops. The decline in growth hormone as we age is known as the somatopause.
Levels of HGH fall with every year from puberty, with the sharpest declines seen in between 20 and forty, with a gradual ongoing decline thereafter. By the time we reach the age of 70 years, average levels have fallen to about 20 per cent of what they were when we were 20.
Benefits of healthy HGH levels
People who retain the highest levels of HGH have the lowest rates of dementia, depression, heart disease and some cancers. The potential importance of HGH to aging is demonstrated by the fact that many of the signs and symptoms of aging are seen in individuals efficient in HGH; including heart disease, bone thinning, expanding waistlines, cognitive decline and shortened life expectancy.
Moreover, restoring healthy HGH levels in deficient individuals can prevent many of these degenerative changes. This finding has led the ‘anti-aging industry’ to suggestion that all of us may also benefit from rejuvenating our HGH to levels seen when we were young. Again, the signs and symptoms of growth hormone deficiency are very nonspecific and may be easily attributed to stress, disease or aging.
If we think that growth hormone levels may be low and impacting on our lives, there are several blood tests that can estimate the effective HGH levels in our bodies.
- Insulin-like growth factor (IGF-1) – this is the most widely used test of growth hormone activity. If you have low HGH levels, the manufacture of IGF-1 (which is partly growth hormone dependent) also falls.
- Insulin-like growth factor binding protein-3 (IGF-BP3) – like IGF-1, the manufacture of IGFBP-3 is growth hormone dependent, and levels fall when HGH is low.
- Growth hormone — measurements of HGH itself are unreliable as it is released in bursts and there may be little serum GH at any given time. However, many stimulation tests are available which tests the ability the brain to release HGH. Two examples are the intravenous arginine and oral L-DOPA stimulation tests. This test is easily performed in a doctor’s office and is becoming more widely available.
Supplementation with HGH
Those with low levels of growth hormone and who are suffering their effects may benefit from supplements. It is illegal and dangerous to use growth hormone in adults outside of this indication.
Treatment starts with a low dose and is adjusted according to each individual’s clinical response until IGF-I levels normalize, significant side effects develop, or the benefits plateau. Women may require a slightly higher dose than men. The success of growth hormone replacement is enhanced if it is combined with other interventions to reduce cardiovascular risk factors (such as adopting a low-fat diet) and improving muscle strength and body composition (such as taking up regular exercise).
It should also be noted, however, that HGH injections cannot replicate the healthy hormone profile of young adults, which is ‘pulsatile’. Interesting new data suggests that our ability to make and release HGH probably remains intact as our bodies age, yet imbalances between inhibitory and stimulatory signals in our bodies lead to declining HGH levels as we get older. New agents that restore pulsatile natural HGH secretion rather than trying to artificially replace it are likely to prove better options for managing deficiency.
Last reviewed 17 November 2012