“Cancer risk increases with the number of years of shift work, the frequency of rotating work schedules, and the number of hours per week working at night. The correlations are so strong that shift work is now officially classified as probably carcinogenic [Group 2A] by the World Health Organization. Other studies of shift workers show increased heart and stroke problems, obesity, and depression. A study of over 3,000 people in southern France found that those who had worked some type of extended night shift work for ten or more years had much lower overall cognitive and memory scores than those who had never worked on the night shift.”

— Circadian rhythms : a very short introduction by Russell J. Foster (Page 29)