Describe the most popular hypothesis for why night workers have an increased risk of cancer

Question

What will be an ideal response?

Answer 1

Although the exact mechanisms are not known, the most popular hypothesis relates to the hormone melatonin. The pineal gland, a tiny pine cone shaped gland (hence the name pineal) in the center of the brain, releases melatonin during the dark phase and inhibits its release during the light phase of the light-dark circadian cycle. Melatonin lowers our body temperature and causes drowsiness which helps us sleep at night. The hormone typically reaches its peak concentration in the middle of the night. However, environmental lighting, such as the lighting in a hospital during the night, will inhibit melatonin production.

Melatonin has an inhibiting effect on the production of estrogen and on the growth and proliferation of cancer cells. Therefore, suppression of melatonin through exposure to light during the nighttime peak concentration periods, likely results in an overall reduced level of blood melatonin levels. The reduced levels of melatonin weakens its ability to suppress estrogen which then has an indirect effect on breast cancer risk. Estrogen is known to directly stimulate hormone-sensitive tumors in the breast. Further, a reduction in melatonin levels directly limits the amount of anticarcinogenic protection this hormone can provide. Schernhammer et al. (2003) note that some studies indicate that colorectal cancer patients have lower levels of melatonin, supporting the contention that suppressed melatonin may be a mechanism explaining the increased colorectal cancer risk for night workers. In addition, the direct anticarcinogenic effect of melatonin applies to other cancer types as well, such as breast cancer.