It had been known since the early 1960s that the thymus is essential for a vigorous immune response. Maestroni reasoned that if a healthy thymus gland requires the presence of melatonin, then melatonin must also be vital to the immune system.

Step by logical step, Maestroni has proven this theory correct. A study he published in 1988 showed the dramatic effect that melatonin can have on the immune system. In this study, Maestroni, Ario Conti, and Walter Pierpaoli injected a group of mice with a sublethal dose of a virus called the encephalomyocarditis virus, or EMCV. As a rule, healthy young rodents will fight off the disease, but mice that have weakened immune systems due to stress or aging will die from it.

After injecting the mice with the virus, Maestroni and co-workers stressed them by confining them for several hours a day in individual tubes perforated with air holes, a procedure called restraint stress. Being confined in the tubes did not harm the mice physically, but it did make them anxious, and anxiety generates stress hormones, which cause a significant decline in the immune response. Then the researchers injected a portion of the mice with melatonin to see if it enhanced their survival.

The mice were observed for the next thirty days. A high percentage of the ones that had not been treated with melatonin died within the first week of the experiment. Meanwhile, most of the melatonin-treated mice managed to fight off the virus even though they had been subjected to the same amount of stress! At the end of the study, 82 percent of the melatonin-treated mice had survived, compared with only 6 percent of those not given the hormone–a striking difference in mortality.

Excerpted from Melatonin: Your Body’s Natural Wonder Drug, Chapter 4, pages 38-39.