Melatonin & Breast Cancer

For billions of years, life on the planet Earth has evolved with about 12 hours of light and 12 hours of dark. We discovered fire a while ago, but have been using candles only about 5,000 years, and electric lighting for only about a century. This is what the country used to look like. Then 20 years later; 20 more years. And then, estimated, about 20 years in the future.

Our skies used to look like this. Now, they look like this. The photo on the left was taken during a blackout. These days, this is the only Milky Way our children will likely ever see.

But, so what? Does it have an effect on our health? (The light, not the candy bar.) Let’s find out. You may have heard that light at night increases breast cancer risk. Is this fact or fiction? Well, two reviews were published last year assessing the existing evidence. “Electric light causes cancer? Surely you’re joking.”

Well, let’s look at the evidence. Smack dab in the middle of our brain is the pineal gland, the so-called “third eye.” And it’s got only one function: produce melatonin in the dark. It’s hooked up to our eyes, and at dawn, the gland shuts down. Then at night, it turns back on. That’s how our internal organs know what time of day it is: they sense the level of melatonin in our bloodstream.
And melatonin is thought to suppress cancer growth, kind of like putting cancer to sleep at night.

Let’s test the theory. If that’s true, should blind women have more breast cancer, or less breast cancer? Less, right? Because their pineal gland never gets turned off by the sun. And guess what? Blindness is indeed protective against breast cancer. Cuts your risk in half.

What about shift workers who work in the middle of the night? Increased risk, right? Melatonin production is interrupted. What if you live in a neighborhood with really bright street lights? Increased risk; they took satellite photos, and the brighter neighborhoods seemed to correlate with greater breast cancer risk.

Anyway, fact—but what does this have to do with nutrition? Last year, for the first time ever, melatonin levels and food choices were studied. The Harvard Nurses’ Study found two foods significantly associated with melatonin suppression—like a bright light at night, which is bad. They looked at fruits, vegetables, nuts, bread, meat, and dairy. In which group were the offenders found?

Both meat and dairy intake were associated with lower melatonin levels, which may help explain why they found that meat and dairy intake in adolescence was associated with breast cancer risk later in life.

To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by veganmontreal.

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• Stevens, R.G. Light-at-night, circadian disruption and breast cancer: assessment of existing evidence. Int J Epidemiol., 38(4):963-70, 2009.
• R. G. Stevens. Electric light causes cancer? Surely you're joking, Mr. Stevens. Mutat. Res., 682(1):1-6, 2009.
• Blask DE, Dauchy RT, Sauer LA. Putting cancer to sleep at night: the neuroendocrine/circadian melatonin signal. Endocrine. 27(2):179-88, 2005.
• E. E. Flynn-Evans, R. G. Stevens, H. Tabandeh, E. S. Schernhammer, and S. W. Lockley. Total visual blindness is protective against breast cancer. Cancer Causes Control, 0(9):1753- 1756, 2009.
• Straif K, Baan R, Grosse Y, Secretan B, El Ghissassi F, Bouvard V, Altieri A, Benbrahim-Tallaa L, Cogliano V. Carcinogenicity of shift-work, painting, and fire-fighting. Lancet Oncol., 8(12):1065-6, 2007.
• Kloog I, Haim A, Stevens RG, Barchana M, Portnov BA. Light at night co-distributes with incident breast but not lung cancer in the female population of Israel. Chronobiol Int., 25(1):65-81, 2008.
• E. S. Schernhammer, D. Feskanich, C. Niu, R. Dopfel, M. D. Holmes, and S. E. Hankinson. Dietary correlates of urinary 6-sulfatoxymelatonin concentrations in the Nurses' Health Study cohorts. Am. J. Clin. Nutr., 90(4):975-985, 2009.

Image thanks to Reigh LeBlanc via flickr

• adolescence
• animal products
• bread
• breast cancer
• breast health
• cancer
• dairy
• meat
• melatonin
• nuts
• sleep
• sunlight
• vegetables
• women's health