To test this hypothesis, the researchers injected human breast cancer cells into laboratory mice. Once these cells developed into cancerous tumors, the tumors were implanted into female rats where they could continue to grow and develop.
The researchers then took blood samples from 12 healthy, premenopausal volunteers. The samples were collected under three different conditions ?during the daytime, during the nighttime following 2 hours of complete darkness, and during the nighttime following 90 minutes of exposure to bright fluorescent light. These blood samples were then pumped directly through the developing tumors.
“The melatonin-rich blood collected from subjects while in total darkness severely slowed the growth of the tumors. “These results are due to a direct effect of the melatonin on the cancer cells,?said Blask. “The melatonin is clearly suppressing tumor development and growth.?/p>
In contrast, tests with the melatonin-depleted blood from light-exposed subjects stimulated tumor growth. “We observed rapid growth comparable to that seen with administration of daytime blood samples, when tumor activity is particularly high,?Blask said.
According to the researchers, melatonin exerts a strong influence on the body’s circadian rhythm, an internal biological clock that regulates sleep ?wake cycle, body temperature, endocrine functions, and a number of disease processes including heart attack, stroke and asthma. “Evidence is emerging that disruption of one’s circadian clock is associated with cancer in humans, and that interference with internal timekeeping can tip the