Nighttime Light and Cancer

Melatonin (N-acetyl-5-methoxytryptamine)

Research Links Nocturnal Light, Melatonin, and Malignancy

Can sleepless nights in front of the TV increase your risk of cancer? What about that streetlight that shines through your bedroom window every night? Could something so familiar and seemingly innocent really contribute to cancer?

We don’t know for sure, but increasing evidence suggests that chronic exposure to light during the night can alter biologic rhythms and interfere with the production of a key hormone. That hormone – melatonin – influences a wide range of physiologic functions, including sleep-wake cycles, fertility, and production of certain chemical messengers and hormones.

Of special importance to women, nighttime release of melatonin may dampen some effects of estrogen, possibly providing protection from breast cancer and other estrogen-related cancers. Some researchers, in turn, suspect that nighttime light’s disruption of melatonin production may increase the risk of these cancers.

Light Pollution

Throughout the ages, humans have sought ways to keep the darkness at bay. But our ability to manipulate the earth’s natural light-dark cycles with artificial light has led to what we now call “light pollution.” Today we are exposed to many more hours of light in a day than our ancestors were.

According to Russel Reiter, Ph.D., a professor of neuroendocrinology at the University of Texas Health Sciences Center at San Antonio and author of Melatonin: Your Body’s Natural Wonder Drug (Bantam Books, 1995), light is a powerful entity – one that promotes good health but also can compromise health if abused. Staying up late in artificially lighted houses and sleeping in bedrooms continually invaded by stray light can rob us of the restorative powers of total darkness, most of which are mediated by melatonin.

Melatonin is secreted from the pineal gland in the brain. Blood levels of the hormone are nearly undetectable during the day but peak at night during darkness. The pineal gland and the eye are functionally linked by neurons. When light enters the eye, melatonin secretion stops. In the absence of light, it increases to up to 10 times its daytime levels.

Nighttime light exposure can alter this normal cycle of melatonin production. Disrupted sleep patterns are an obvious consequence, with potentially negative effects on mood, cognitive abilities, and immunity. An increased vulnerability to cancer, though not yet proven, may be a more insidious problem.

The Cancer Connection

Animal experiments conducted in Germany in the 1930’s turned up the first link between melatonin and cancer. In those studies, giving tumor-bearing mice extracts from the pineal gland (which presumably contained melatonin) slowed tumor growth. In studies conducted in the 1960’s, rodents whose pineal glands were removed grew larger tumors than did animals with intact glands.

Later laboratory experiments confirmed that melatonin could inhibit the growth of human cancer cells. In some experiments, melatonin specifically inhibited the stimulatory effects of estrogen on some cancers, much as tamoxifen does.

Nighttime light’s ability to interfere with melatonin’s anti-cancer properties has been shown in a series of experiments conducted at the Bassett Research Institute in Cooperstown, N.Y. A team led by David Blask, M.D., Ph.D., a research scientist in experimental neuroendocrinology/oncology, implanted liver tumors in rats and then exposed the animals to different lighting conditions. Tumors grew nearly twice as rapidly among rats exposed to stray light at night as among those kept in total darkness.

Epidemiologic studies suggest a similar light-melatonin-cancer connection in humans. A study published in The Lancet found that female flight attendants have a twofold increase in breast cancer risk. The researchers speculated that chronic disruptions in the women’s sleep-wake cycles (jet lag) led to melatonin deficiency and, in turn, to breast cancer.

In a study published in the journal Epidemiology in 1991, researchers at the Centers for Disease Control and Prevention found that blind women were half as likely to develop breast cancer as were similar women who could see. (Because profoundly blind people don’t perceive light, their melatonin cycles persist.)

More recent studies have confirmed and expanded these results. In a Swedish study published in Epidemiology, researchers compared cancer rates among profoundly blind individuals and people with severe vision loss but the ability to perceive light. Study participants who could still perceive light had cancer rates equivalent to those of the general population. The profoundly blind individuals, in contrast, were 30% less likely to develop cancer.

Finally, Dr. Blask notes that early clinical studies suggest that adding melatonin to standard cancer therapy may slow the growth of some tumors. So far, these studies have involved very small numbers of patients – all in the most advanced stages of cancer.

Enhance Your Melatonin Production

Dr. Reiter offers a number of suggestions to help you live a melatonin-friendly lifestyle:

• Get enough sleep to wake fully refreshed
• Increase your exposure to natural sunlight or use a full-spectrum light box. (Morning exposure is best)
• Decrease exposure to bright light at night (Use red or yellow light, which appear to interfere less with melatonin production.)
• Light-proof your bedroom. Install light-blocking curtains o use eye shades.
• Curb alcohol intake. Alcohol is associated with decreased melatonin levels.
• Eat melatonin-rich foods (oats, sweet corn, rice, ginger, tomatoes, bananas), especially at night.
• Eat foods rich in calcium, magnesium, vitamin B6, and niacinamide or take supplements of these nutrients.
• Spend time each day in meditation or prayer.
• Practice stress-reduction techniques, which can enhance melatonin production.

Additional Notes:

Other foods/herbs that contain melatonin-like molecules are: barley, walnuts.

Tryptophan is a precursor of the sleep-inducing substances serotonin and melatonin.

These are foods high in the sleep-inducing amino acid tryptophan:
• Dairy products: cottage cheese, cheese, milk
• Soy products: soy milk, tofu, soybean nuts
• Seafood
• Meats
• Poultry
• Whole grains
• Beans
• Rice
• Hummus
• Lentils
• Hazelnuts, Peanuts, walnuts, almonds
• Eggs
• Sesame seeds, sunflower seeds, pumpkin seeds

Foods rich in melatonin include: Oats, sweet corn, rice, ginger, tomatoes, bananas, cherries and barley. There are several herbs that contain even higher amounts of melatonin that could be used as an evening tincture; feverfew, St. John’s wort, mustard seed, fennel seed, lemon verbena and balm mint. Wine, both red and white contain melatonin also.

And don't neglect your intake of B-6. In animal studies, pyridoxine (vitamin B-6) also appears to be necessary for the production of serotonin from tryptophan.

Although I wrote this article quite a few years ago, a quick search of the literature finds that the link between melatonin and cancer prevention is stronger. Melatonin has also been found to be important to the nervous system and skeletal system.

Previously Published in “Women’s Health Advocate”, February 1999