Why light at night is bad for your health

IN the beginning, God created day and night.  Genesis 1:3-5 recorded: “God said, ‘Let there be light,’ and there was light.  God saw that the light was good, and he separated the light from the darkness. God called the light ‘day,’ and the darkness he called ‘night.’ And there was evening, and there was morning – the first day.”

Then man invented electricity, which acts as a middleman between energy resources, such as coal or falling water, and the final use of that energy. Because of electricity, man can have the light he needs even at night.

Man considered electricity as good.  But recent studies show there are bad sides that artificial lights bring. “Sleeping at night with the lights on or with some source of light from outside the window—like a street lamp post—can be bad for the health,” said Dr. Rafael R. Castillo, a medical doctor who writes a regular weekly column for Philippine Daily Inquirer.

Doing so may increase a person’s risk of getting any of these cancers: breast, colon or prostate. Dr. Willie T. Ong, an internist-cardiologist and author of several health books, noted: “As the scientific evidence grows, the World Health Organization has already concluded that working during the night shift is probably carcinogenic [cancer-causing].”

Among those who are most likely to develop any of the aforementioned cancers are people who work at night, especially call-center agents, security guards, entertainers and night-shift workers (particularly those who work in factories and hospitals).

But it seems these days people who are not working at night may not be spared at all.  Pat Hagan, in an article published in Daily Mail, wrote: “Artificial light has transformed how the human race has lived in the past 100 years or so. Even for those not working night shifts, it can be almost impossible to avoid the night-time glare from street lamps, car lights, TVs, computers and smartphones.”

“Light is a stimulus that can have impacts on health, well-being and performance,” for good and ill, Dr. George Brainard, professor of neurology at Thomas Jefferson University, told USA Today.

Prof. Abraham Haim, a researcher from the University of Haifa, said the culprit is the disruption of one’s body clock. Kim Palmer, author of the USA Today feature, wrote: “Light has this power because it drives our central circadian clock. Ideally, that internal clock produces daytime alertness and nighttime sleepiness on a predictable 24-hour schedule. Receptors in our eyes play key roles, taking their cues from the intensity and wavelengths of light we are exposed to each day and night.”

Exposure to short-wavelength light at night has been shown to suppress melatonin production, thereby disrupting the internal body clock, which can affect sleep and overall well-being. However, it has been postulated that the disruption of the internal body clock by reducing nocturnal melatonin might also increase the incidence of disease. 

“Low levels of melatonin have been linked to bad health effects, such as inflammation, weaker immune system and faster cancer growth,” wrote Dr. Ong. A lack of melatonin has also been linked to diabetes, obesity and heart diseases. 

In 2012 the Lighting Research Center (LRC) in the United States published a study showing that two-hour exposure to light from self-luminous devices can suppress melatonin by about 23%.

Prostate cancer

After lung cancer, prostate cancer  is now the second-most common cancer among Filipino males. The 2010 statistics from the Department of Health (DOH) showed about 6 million Filipino men over the age of 50 are susceptible to develop the disease.

Most likely the figure will go up if more Filipino men sleeping with artificial lights on. A research was conducted by Prof. Haim and Prof. Richard Stevens of the University of Connecticut among men in 164 countries. 

“The results show that countries with high light at night exposure had the highest incidence of prostate cancer at 157 prostate cancer cases per 100,000 people,” wrote Dr. Ong in his book, Doctors’ Health Tips and Home Remedies. “In comparison, light at night exposure had only 67 prostate cancer cases per 100,000 people [50 percent less].”

Dr. Ong observed: “Although this study is by no means definitive, it shows curious link between light at night exposure and prostate cancer.”

Breast cancer

The health department and the Philippine Cancer Society Inc. (PCSI) considered breast cancer as the most common form of cancer in the country—particularly among women.  “One out of every 13 Filipino women is expected to develop breast cancer in her lifetime,” according to a document released by the Asian Hospital and Medical Center (AHMC). 

The Geneva-based United Nations health agency reports that 1 out of 4 women who are diagnosed with breast cancer die within the first five years. What is even alarming is that all women are at risk, with approximately 70 percent of breast cancers occurring in women without the known risk factors.

American researchers from Harvard Medical School and Brigham and Women’s Hospital, both of Boston, have found out that “women who work night shifts have a higher risk of breast cancer.”

“Because night-shift work has become very common in developed countries, future studies should assess the relationship of light exposure to the risk of other cancers and consider the risks in men,” team leader Dr. Eva Schernhammer told Journal of the National Cancer Institute.

Another study suggests that “reduced melatonin output at night allows an increase in levels of another hormone, estrogen, which is involved in the development of two in every three cases of breast cancer.”

Colon cancer

In the Philippines colon cancer is the fourth most common cancer, according to the Philippine Cancer Society Registry.  It comes after breast, lung and liver cancers.  But unlike the first three cancers, colon cancer is not openly discussed. 

“Among cancers, colon cancer  stands out as a disease that can be largely prevented, but few people believe it will happen to them,” said Dr. Atenodoro Ruiz Jr., a gastroenterology consultant at The Medical City and a diplomate of the American Board of Internal Medicine in Gastroenterology and of the Philippine College of Physicians in Internal Medicine.

Some studies suggest working a night shift regularly may increase the risk of colon and rectal cancer. “It is thought this might be due to changes in levels of melatonin in the body,” the American Cancer Society surmised, adding that more research is still needed.


Aside from getting cancer, an American-Israeli study showed that exposure to bright lights at night may cause obesity.  In laboratory studies, Ohio State neuroscientist Dr. Randy Nelson and Prof. Haim showed that mice exposed to 24 hours of constant daylight gained more weight compared to mice exposed to only 16 hours of daylight. After eight weeks, the mice exposed to constant light had 50-percent weight gain compared to the other group.

“Something about light at night was making the mice in our study want to eat at the wrong times to properly metabolize their food,” Dr. Nelson reported.

The researchers also believe that disruption in one’s body clock and lack of sleep can make people eat more often and at the wrong times. “Light at night is an environmental factor that may be contributing to the obesity epidemic in ways that people don’t expect,” Dr. Nelson added. 

Obesity is fast becoming a big health problem in the country. “Among the six countries studied, the Philippines has the second-lowest obesity and overweight prevalence at 5.1 percent and 23.6 percent, respectively. But despite low prevalence rates, obesity has a strong impact in the Philippines due to the large number of obese persons in the country—18 million Filipinos are obese and overweight,” said the newly released report. “Tackling obesity in Asean: Prevalence, impact, and guidance on interventions.”

Last year, obesity cost the Philippines between US$500 million and $1 billion or equivalent to between 4 percent and 8 percent of its health-care spending. “This makes the country the fourth-highest spender for obesity-related problems,” the report said.

Some tips

In his book, Dr. Ong—who wrote the book in collaboration with his wife, Dr. Liza Ong, also a medical doctor—shared some tips to get your body clock working perfectly. This can translate to more energy and better health:

  • Sleep at around the same time every night and wake up at the same hour. This technique will keep your body clock in harmony.
  • Limit your light exposure at night. It’s not scientifically proven yet, but you can try to avoid very bright lights at night, especially within three hours of bedtime.
  • Limit computer time at night, maybe less than half an hour. When you sit in front of the strong glare of the computer screen, this could suppress your body’s melatonin production.
  • Although exposure from watching TV is only minimal, make sure you sit several feet away from your TV set.
  • In your bedroom, draw up the window curtains to limit glare from the streets.
  • Use yellow or red light instead of white light at night. According to George Brainard, a professor of neurology at Jefferson Medical College in Philadelphia, temporarily turning on a bright white light at night during your bathroom visit may disrupt the production of melatonin. 
  • Melatonin supplements may be useful in certain cases. According to Prof. Brainard, “Night-shift workers might consider taking a supplement right before they go to sleep in the morning. Those who travel internationally can try it to reset their body’s clock and avoid jet lag.” Consult your doctor about this.
  • Be exposed to sunshine during the day. Early-morning sunshine is best and it activates the body’s natural rhythm. 
  • During the day, get exposed to indirect sunlight. Avoid staying in a dark room all day. The purpose of this “light at daytime” and “dark at night” routine is to make sure your body knows when it is day (time to work) and when it is night (time to sleep).
Image Credits: Blackstudiopl | Dreamstime.com, Ximagination | Dreamstime.com, www.freepik.com

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