Weight, age, number of pregnancies – these are all factored into a woman’s risk for breast cancer, but what about exposure to artificial light? Did you know that women who are exposed to longer periods of light are at a greater risk for developing breast cancer?

The effect of artificial light on melatonin production is the cause of the increased cancer risk. “Researchers have found that low melatonin levels in premenopausal women are associated with an increased risk of breast cancer,” ScienceDaily reported in their article, “Low Melatonin Associated with Increased Risk of Breast Cancer in Postmenopausal Women.”


Artificial Light Suppresses Melatonin Production

Melatonin levels in the body rise in the evening and remain high throughout the night. They drop off early in the morning. The reason is that melatonin production is affected by light. More melatonin is produced when it is dark, and exposure to light can cause melatonin levels to drop. Drowsiness is a side effect of melatonin, which is why it is used as a sleep aid.

According to the National Institutes of Health article “New Research Shows Artificial Light at Night Stimulates Breast Cancer Growth in Laboratory Mice,” a Bassett Research Institute study shows that “nighttime exposure to artificial light stimulated the growth of human breast tumors by suppressing the levels of melatonin. The study also showed that extended periods of nighttime darkness greatly slowed the growth of these tumors. [This] might explain why female night shift workers have a higher rate of breast cancer.” In fact, breast cancer is more prevalent among women of industrialized nations such as the United States. Conversely, women who are exposed to longer periods of darkness are less likely to develop breast cancer.

Melatonin Blocks Cancerous Tumor’s Ability to Use Conjugated Linoleic Acid

This link between breast cancer and light may have to do with melatonin’s effects on linoleic acid, an essential fatty acid. According to David Blask, M.D., Ph.D., the lead author of the Bassett Research Institute study, tumors often need linoleic acid to grow. Melatonin blocks the tumor’s ability to use linoleic acid, which prevents the tumor from growing.

They supported this theory by injecting melatonin-rich blood into the cancerous tumors, which slowed the growth of the tumors. Tumor growth increased when they injected blood with low melatonin levels.

There are different types of linoleic acid. Some promote cardiovascular health and work as antioxidants, fighting free radicals that can cause cancer. Conjugated linoleic acid promotes weight loss, but cancerous tumors use this fatty acid to grow. Maintaining proper melatonin levels is important in order to reap the benefits of conjugated linoleic acid without increasing the risk for cancer.

The best way to combat cancer caused by artificial light is to sleep and wake with the sun. Go to bed at a regular hour, keeping the bedroom as dark as possible. If you need to get up in the middle of the night, keep the lights off, or only use night lights, but never in the bedroom. This is important because turning on lights can cause melatonin levels to drop to abnormal levels for nighttime.

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