What’s more, night time and sleep are the time our circadian rhythm cycles down activity so we can renew and repair cells as well as detoxify poisons. If we do not sleep well we tend to feel horrible because the accumulating toxins do not get removed but instead sit in the cells where they continue to damage cell respiration and many other cellular processes causing yet another potential setup for cancer.
There is no shortage of evidence of a link between insufficient sleep and the risk of cancer. In particular, people with circadian rhythm disorders—in which the body's biological clock is disrupted because of shift work are at increased risk. Researchers suspect that the disruption in the circadian rhythm poses a risk for developing cancer because the body's internal clock affects so many biological functions. One theory is that the suppression of melatonin at night (which comes from exposure to bright light) could be partly responsible. Indeed, scientists have seen this link in animal studies; for example, when they manipulate the sleep/wake cycles of rodents for an extended time, cancers grow faster. The disturbance in circadian rhythm caused by shift work may also increase the prevalence of gastrointestinal problems. Peptic ulcer disease is more common in shift workers.
Interestingly, the hardest to kill cancer cells have completely turned off their internal clocks so they can eat 24/7. And even more interesting is the recent discovery at the Ludwig Cancer Research Center that sodium bicarbonate turns the circadian rhythm back on making the toughest cancer cells easier to kill.
One study showed that insufficient sleep might contribute to breast cancer recurrences among postmenopausal women and the development of more aggressive forms of breast cancer. Another study suggests that disrupted sleep increases prostate cancer risk. Lack of sleep distorts our genes, and increases our risk of death. Insomnia disrupts the creation of sex hormones like estrogen and testosterone, and leads to premature aging.
A study in the International Journal of Cancer found a relationship between women's irregular work schedules and the rate of breast cancer. Researchers compared 1200 women who had developed breast cancer between 2005 and 2008, with 1300 women who did not have a cancer diagnosis. They found that the rate of breast cancer was 30 percent higher for the women who had worked shifts.
Insomnia is defined as “An inability to fall asleep or remain asleep long enough to feel rested, especially when the problem continues over time.” In an effort to combat this, as many as 25 percent of the people in the United States use medications to help them sleep.
 BMJ 2019; 365 doi: https://doi.org/10.1136/bmj.l2327 (Published 26 June 2019) Investigating causal relations between sleep traits and risk of breast cancer in women: mendelian randomisation study