We should not think of melatonin as the only influence on aging. In a complex organism such as the human body there are countless factors influencing the aging process. The pineal gland is only one of these factors, albeit an important one.
Some of the ways melatonin could prolong life span include its ability to enhance the immune system, regulate hormonal levels, and act as an antioxidant. There's also an interesting correlation between diet and melatonin. Food restriction in rodents causes an increase in melatonin production (Stokkan, 1991). Food restriction also leads to their life extension. It is too early to tell whether the increase in melatonin due to food restriction causes this longevity (Huether, 1994).
A Powerful Antioxidant
Many diseases are now believed to be caused or aggravated by free radicals. A free radical is any molecule with an unpaired electron restlessly going around ravaging and harming other molecules— like a hyperactive child swirling around a playpen breaking toys. Free radicals are formed as the end result of burning glucose and other energy molecules within our cells. When we drive a car, we burn gasoline as fuel. The leftovers are spewed out through the tail pipe of the exhaust system. When food is broken down and then metabolized, it similarly creates byproducts. These free radicals are some of the harmful molecules that are left over. They include molecules called hydroxyl (OH•), superoxide (O2• –), and hydrogen peroxide (H2O2). Hydroxyl radicals are thought to be the most damaging (Reiter, 1994).
In the past few years researchers have found that melatonin possesses unique properties as a free radical neutralizer. Melatonin is not only able to trap free radicals such as superoxide anions, but is also very efficient at preventing damage from hydroxyl radicals. Melatonin has been found to be the most potent neutralizer of hydroxyl radicals ever detected. It stops damage immediately and is more effective as an antioxidant than even vitamins C and E (Hardeland, 1993). It also stimulates the enzyme glutathione peroxidase, which converts destructive hydrogen peroxide, H2O2, to safe water, H2O (Reiter, 1993). Researchers in France have also confirmed melatonin's antioxidant abilities (Pierrefiche, 1993).
Many antioxidant vitamins and nutrients lack the capacity to enter cells and organelles as easily as does melatonin. Melatonin has the advantage of being able to freely enter and permeate all parts of a cell. In a study of DNA damage induced by safrole, a cancer promoting agent, melatonin protected the DNA almost entirely from free radical damage (Tan, 1994). This occurred even though melatonin was given at 1/1000 the dose of the carcinogen. Melatonin also has been found to bind to chromatin within the nucleus of a cell, thus indicating that it may have direct on-site protection of DNA. As discussed earlier, melatonin levels decrease as we age. Researchers speculate that lower melatonin levels may not be able to protect brain cells (neurons) from normal wear and tear. Furthermore, the activity of some brain enzymes, such as MAO-B, monoamine oxidase type B, can increase with age, leading to more breakdown of neurotransmitters and more free radical production. The failure of neurons and the decline of neurotransmitters may then accelerate, leading to dementia, Alzheimer's disease, Parkinson's disease, and other degenerative mental illnesses. As Hardeland and associates concluded in their 1993 article, "Melatonin promises to become a powerful pharmacological agent with its unique properties as a nontoxic, highly effective radical scavenger which provides protection eventually from neurodegeneration as well as from the mutagenic and carcinogenic actions of hydroxyl radicals." In other words, melatonin, taken as a supplement, could slow down the aging process and decrease the incidences of brain damage and cancer.