Evidence from animal studies
Weindruch and Walford have shown that dietary restriction produces strong effects on the endocrine (hormonal) system. They have also reviewed the work of many scientists who hold to a view different from that which sees ageing as the result of what happens in cells. The contrary view suggests that ageing has more to do with signals delivered by hormones, probably working in collaboration with the nervous system. Hormones are powerful chemical messengers and evidence exists of regeneration of tissues which have aged (possibly due to a decline in hormone levels) once hormone levels are topped up.

An example of this is provided by what happens in rats when growth hormone is implanted into them. Another important hormonal centre, the thymus gland, which often shrinks with age, is found to regenerate when growth hormone is implanted into elderly rats, resulting also in a marked improvement in immune function (with which the thymus is intimately involved). Similar regeneration is seen, but this time in nerve and brain tissue, when nerve growth hormone is infused into the brains of elderly rodents. Aspects of their memory are seen to improve as a result.

This shows that growth hormone might have a profound effect on complex organizational systems (such as hormonal, nervous, and immune systems) which together might be the elements which decide on the speed and sites of ageing. But how can humans improve their growth hormone levels? And what about 'natural' stimulation of growth hormone?

This brings us back to Pearson and Shaw, and their promotion of arginine and/or ornithine. These two amino acids are present in your diet every time you eat a complete protein such as eggs, cheese or fish. When you take them as supplements they arrive in your body to join a pool of free amino acids derived from your food, where they wait for distribution and use in new protein synthesis or, in the case of ornithine, for use in body processes such as detoxification, transportation and metabolism.

When amino acids (the building blocks of protein) are used on their own in this way they act in a pharmacological manner, rather than as they would were they to be eaten as part of a food. It is in this way that they stimulate growth hormone production by the pituitary gland. Leslie Kenton, writing in Ageless Ageing (Century Arrow, 1988) extols their virtues but settles for ornithine as the most useful:

Ornithine is an excellent growth-hormone stimulator thanks to its action on the central nervous system. In fact it is twice as active as arginine. And it has an ability which arginine doesn't have - it can actually be transported to the mitochondria, the cell's energy factories. Many physicians and nutritionists who use growth hormone stimulants recommend taking ornithine alone instead of both.

A suggested supplement dosage of ornithine is 4 grams daily (good health food stores and most pharmacies stock it) taken with water, say 2 grams in the morning and 2 grams in the evening, away from meal times. A few months on such a regime should show results in terms of less fatty tissue and firmer skin and body generally, although whether this on its own can in any way translate into life extension seems doubtful. Were arginine used in preference to ornithine, approximately twice the dosage would be suggested, as long as the cautions given below are adhered to.

Cautions
Whether either ornithine or arginine are used to stimulate growth hormone beware of possible side-effects of excessive growth hormone stimulation: