This hormone plays a vital part in all aspects of growth (especially in the young) and repair (which calls for enhanced protein synthesis), as well as having a beneficial influence on immune function. It is produced in the anterior pituitary gland (at the base of the brain) and the efficiency of its production is known to decline with age, so that by 60 years old almost a third of us have no growth hormone production at all. Not surprisingly, this is seen to be a key factor in the speed with which we age.

Among the stimulants which encourage production of growth hormone are peak level exercise (not just any exercise, only that which pushes you to the limit, such as aerobic), trauma (peak level exercise has a minor traumatizing effect on muscle, and this might be the trigger for growth hormone), fasting, sleep (but more so in young people) as well as the specific amino acids mentioned above.

In 1990 a remarkable research study, carried out by Dr Daniel Rudman, of the Medical College of Wisconsin, was reported in the New England Journal of Medicine. A group of 21 elderly men (age 61 to 81) were tested over a six month period, 12 of them receiving injections of synthetic growth hormone three times weekly, the other nine receiving no treatment (for comparison of results of those treated and those untreated). The diets of all 21 were kept much the same (protein 15 per cent of intake, carbohydrate 50 per cent and fats 35 per cent) with no change at all recommended in smoking and other habits. Those who received the hormone showed marked benefits at the end of the study:

• Increase in growth hormone levels in the blood to that of 40 year olds.

• Decrease of fatty tissue by 15 per cent

• Increase in lean body mass (mainly muscle) by 9 per cent

• Increase in density of bone (vertebrae) by 1.6 per cent

• Increase in skin thickness by 7 per cent

In many respects it was found that the men who received growth hormone appeared physiologically to be 10 to 20 years younger than when they started just six months previously. Subjectively the men felt trimmer, more energetic and healthier, noting firmer skin, less fat and more muscle. Not surprisingly none of the improvements or subjective feelings were seen or reported in the nine who received no treatment.

Cautions
Caution is called for, warn the researchers running this test, for the following reasons:

1. Growth hormone replacement can cause diabetes, arthritis and high blood pressure. Although none of these occurred during the trial, long-term problems could arise if use continued indefinitely.

2. The cost is over £8,000 for a year's supply of growth hormone.

3. There was no improvement in brain or eye cells, nor in elastic tissue.

This means that it almost certainly has no effect on free radical damage or DNA repair, although the results in terms of improved lean body mass shows that it does enhance protein synthesis. So, if the use of synthetic growth hormone does not reverse the ageing process totally, merely selectively, and if it has no proven effects on life-extension, would 'natural' growth hormone be different?