Night shifts disrupt the body clock and may raise the risk of dementia, heart disease and cancer

An increasing number of individuals are working during the night and sleeping when their internal body clock signals them to stay awake. Recent research has established links between shift work and chronic sleep disruption to a higher risk of dementia, heart disease, metabolic disorders, and certain types of cancer. A new study suggests that the timing and intensity of light exposure during the day can also impact when people fall asleep and the quality of their rest.

Dr. Amit Green, a sleep psychologist at Assuta, emphasized that light is the primary signal that regulates the body's internal clock. "In today's world, we experience insufficient natural light during the day, particularly when we work indoors or remotely," he explained. "Conversely, at night, we are exposed to excessive artificial light from lamps and screens."

The body's internal clock receives light information from the eyes and adjusts melatonin production accordingly. "Melatonin plays a role in regulating sleep and wakefulness, as well as immune system function, cognitive function, and digestion," Green noted. Exposure to light at inappropriate times can disrupt the body's circadian rhythm, increasing the risk of illness for night-shift workers.

The effects of night work are not solely determined by the duration of sleep. It may also involve disruptions to essential processes that occur during sleep. During deep sleep, the brain consolidates memories, processes emotions, and releases growth hormone, which is crucial for physical recovery, tissue repair, and muscle maintenance.

The glymphatic system, responsible for clearing waste from the brain during sleep, is also active during this time. Waste products include proteins linked to Alzheimer's disease, and poor-quality sleep impairs the clearance process, potentially increasing the risk of dementia and other illnesses. A review of a study by the BBC analyzed brain scans from over 40,000 people, identifying those with impaired brain waste-clearance systems.

These individuals were more likely to develop dementia later in life. However, the study's authors stressed that their findings only suggest a possible connection. Other factors, such as high blood pressure, smoking, and diabetes, may also influence dementia risk. A Swedish study involving over 13,000 shift workers found that working night shifts during middle age increased the risk of dementia by 36%.

The risk grew with the number of years spent in shift work. The health risks associated with night work extend beyond the brain. Restricting sleep to about 4.5 hours per night for three consecutive nights significantly increased immune system activity, potentially promoting inflammation and heart disease. Disrupted sleep can also elevate cortisol levels, a stress hormone associated with insulin resistance and diabetes.

Cortisol may further exacerbate sleep disturbances, creating a self-reinforcing cycle. The World Health Organization's International Agency for Research on Cancer has classified night-shift work as "probably carcinogenic to humans," placing it in the same risk category as red meat, based on possible links to breast, prostate, colon, and rectal cancers.

Possible explanations include disrupted melatonin production, limited daylight exposure, and chronic low-grade inflammation resulting from sleep disturbances. However, the classification does not imply that night work inevitably leads to cancer.