Not all of the hormones produced in our bodies decline with aging.
Estrogen, made by the ovaries, declines dramatically only after menopause. Melatonin, made by the pineal gland, declines progressively as the decades march on. DHEA and DHEAS, made by the adrenal glands, also progressively drop with aging starting in our late 20's. However, other steroids made by the adrenal glands, such as cortisol and aldosterone, stay relatively stable throughout life. Furthermore, the amount of androgens produced by the testicles drops only slightly with aging.
A number of changes occur in our bodies as we age. There's a substantial reduction in protein synthesis leading to shrinkage in muscle mass, and decreased bone formation leading to osteoporosis. Many researchers think that these changes are closely related to the age-associated decline in hormones. Some even think that restoring these declining hormones could 1) delay muscle wasting, 2) strengthen bones, 3) maintain a healthy heart, and 4) slow the progression of aging..
From Infancy to 120--DHEA throughout life
The pattern of DHEA(S) production by the human body is interesting. Although a fetus makes DHEA(S), and this hormone is present in a baby for the first few months of life, there is very little made from 6 months up to the beginnings of puberty. From then on the levels continually rise and peak in our 20's. From our 30's on, there is a progressive decline in DHEA(S) levels (Orentreich, 1984). It is estimated that by age 70 we only make a fourth of the amounts made in our prime, and by age 90, perhaps a tenth (Migeon, 1957, Birkenhager-Gillesse, 1994, Ravaglia, 1996). One study has found that there is a 60% decrease in DHEA and DHEAS between ages of 40 and 80, alone! (Belanger, 1994).
Since DHEA is the precursor to androgens and estrogens, the decline in DHEA production also reflects itself in the cells of our bodies. It is thought that at least half of the androgen and estrogen precursors in our body comes from DHEA. The rest are made from the testicles and ovaries.
After menopause, when the ovaries are practically no longer functioning, 100% of the estrogen precursors comes from the adrenal glands' DHEA (Labrie, 1991).
From mice to men, and women
Most of the longevity studies showing increased lifespan with DHEA have been done on rodents (Lucas, 1985). Although the majority of these studies confirm a lifespan-extending effect with DHEA, we should keep in mind that, unlike humans, rodents have little circulating DHEA(S) in their blood (Nestler, 1995). This, alone, should caution us about jumping to conclusions based on results of animal studies. This was emphasized by Dr. Peter Hornsby, from Baylor College of Medicine in Houston, Texas, when he wrote, "Although experiments in rodents on the effects of DHEA have been extremely valuable, we should always bear in mind the difficulty in applying rodent data to humans... In rodents, tissues may respond to DHEA quite differently since they do not normally have high levels of DHEA in their plasma."
Countless rodent studies have been done with DHEA that have shown increased lifespan and positive influences on a variety of illnesses such as heart disease, diabetes, and cancer. I have purposely chosen not to focus on these studies because conclusions from these studies extraploted to humans could be misleading and inaccurate. As much as possible, human studies have been emphasized in this book.