According to data from the April 1995 Journal of NIH Research, a healthy 10-year-old might secrete 2000mcg HGH per day. By age 20 hGH secretion has already dropped to 700mcg per day (a 75% drop!). 400mcg is secreted on average by 30, while from 40 to 80 hGH drops from about 325mcg to 225mcg per day.
In children and adolescents, the rate of growth in height is primarily determined by the rate at which endogenous GH is secreted. The growth spurt during puberty is caused by increased secretion of GH, secondary to increased secretion of gonadal steroids. Under normal conditions, both GH secretion and growth rate remain increased until the first appearance of menses in girls or thicker facial hair in boys and begin to decline during the development of full pubic hair until final height is reached, after which GH secretion is reduced to a steady state.
While manufacturers clearly identify the recommended starting dose for each FDA-approved use of their rhGH products, doses reported among reviewed studies vary greatly for both approved and nonapproved indications. Doses vary with the rhGH product used as well as the disease process being treated. Since not all researchers identify the rhGH product under investigation and many report dosage by body surface area (m2) rather than weight (kg), it is difficult to determine whether lower-than recommended dosing induces adequate catch-up growth or higher-than recommended dosing increases the incidence or severity of adverse effects. The frequency of rhGH injections also varies greatly, ranging from 2 to 7 times a week in studies and 3 to 7 times a week in manufacturers' instructions. However, some data indicate that a weekly dose of rhGH divided into daily injections increases growth rate to a better degree than the same weekly dose divided into three injections in patients with GH deficiency and those with Turner's syndrome. In contrast, twice-daily injections appear to be no more effective than once-daily injections. Some data also suggest that evening injection produces hormone and metabolite patterns that are significantly closer to normal than those achieved with morning injection.
Regardless of diagnosis, the optimal age for initiation of rhGH therapy has not been determined. Much data indicate that rhGH should begin as early as possible following diagnosis of a height deficit or a disorder known to be associated with a height deficit. Several groups have found greater benefits with rhGH before rather than during or after puberty and have recommended initiating rhGH several years before puberty; however, the actual pubertal rhGH benefit is difficult to assess if there has been no control for gender growth differences and spontaneous versus steroid-induced puberty.
When to discontinue rhGH is also not resolved. Researchers variously report ending therapy when the epiphyses have fused, when growth rate decreases to 2.5 cm/year, when bone age suggests no further height potential, or when patients reach the 50th percentile for target height, fall within the 3rd to 10th percentile for normal height, or achieve a height consistent with midparental height. These can range from the ages of 13 to 23 for different individuals. It is important to stop rhGH as soon as possible to prevent side effects, minimize cost, and avoid disappointed expectations as length of dose is not necessarily directly related to increase in height. However, it is also necessary to consider additional benefits of rhGH, including improvement in bone structure, body muscle/fat composition, and protein/lipid metabolism. Although continued growth may no longer be possible, some patients, such as those with GH deficiency, may benefit from rhGH therapy in adulthood since discontinuation of rhGH after final expected growth leads to deterioration in these other parameters.
Can you tell us more about your brother's development? How far along in puberty is he?
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Yours in sport,
George
George Spellwin
Research Director
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