Afraid of our shadows?

This morning, I get up and do a quick scan of The New York Times and my Facebook feed. A professional acquaintance posts a link to a story written by another professional acquaintance on Healthymagination, the GE-sponsored health website.

Apparently, the post says, researchers at Yale and Israel’s University of Haifa have done studies that link nightshift work and sleeping in a lighted room to a slight increase in breast cancer risk. The Israeli study, for instance, finds that light in the bedroom may increase breast cancer risk by 22 percent (if the risk is 1 in 100, for instance, this would bring the risk to 1.22 in 100). Yale scientists found than long-term shift work at night may lead to the expression of genes that make some women more susceptible to breast cancer. At the University of Virginia, researchers are exploring whether changes in circadian rhythms might lead to malignancies.

I groan when I first read this story: We breast cancer patients already have to worry about our intake of soy (soybean isoflavones have estrogen-like properties and estrogen triggers some cancers, including mine), meat, eggs and milk treated with hormones (same estrogen worries), processed food (transfats seem to increase risk). We’re not supposed to let ourselves get too heavy. We’re supposed to curtail our social drinking to near monastic levels. Of course, smoking is taboo. A couple studies have shown that eating more poultry, dairy, fiber and fresh veggies increases survival rates. I’m sure I’m leaving out about a dozen other things that we’re supposed to do/not do. Now, here comes research that we’re supposed to be afraid of our own shadows? Well, at nighttime at least.

I guess I’m glad that researchers are leaving no stone unturned to understand the complex causes of breast cancer. But I’m not going to run around the house unplugging all the nightlights just yet. Here’s why:

• The Israeli study that found the 22 percent increase in risk is indeed large, analyzing the habits of 1,679 women. In science, the larger the sample, the more reliable the results. So, half of these 1,600-odd women have breast cancer; and they were questioned about their night lighting habits. But, as another acquaintance just posted on Facebook, correlation does not equal causation. Maybe some of the study subjects shared other habits, like eating peppermints. Does this mean peppermint causes breast cancer?

• The Yale researchers found that two decades of night-shift work can lead to changes in a gene that governs our sleep-wake cycles. These changes MAY lead to the expression of genes that MAY increase breast cancer risk. This is hardly a smoking gun; it’s more like your kid pointing thumb and forefinger at you and saying, “Bang!” Maybe future research will solidify these linkages, but as yet, it’s hardly clear.

• And is it the act of working at night that causes a slight increase in breast cancer risk? Or, might it be that the kinds of work done at night—factory work, cleaning, driving delivery trucks—heighten risk?

• The story mentions that earlier studies have found that women with breast cancer have decreased melatonin, a chemical that regulates sleep. I can attest to the insomnia that accompanies breast cancer. But: Did the decrease in melatonin cause my breast cancer? Or did the breast cancer cause my melatonin levels to dip? It’s unclear.

• Finally, the only one of these studies that assigns actual numbers to breast cancer risk is really quite small: The 22 percent increase in risk found by the Israel team sounds large, but it’s not. The latest numbers show the lifetime risk of developing breast cancer is 1 in 8; this study says that nighttime light increases the risk to 1.22 in 8 (from a 12.5 percent risk to a 15 percent risk, if you prefer percentages). Maybe. That’s not nothing, but lately, I’ve been dealing with numbers that are much bigger. For instance, taking tamoxifen (an anti-estrogen) for five years after the rest of my treatment will decrease my risk of recurrence by 50 percent. That’s a number large enough to really make me change my behavior.

These studies are interesting, but hardly conclusive evidence. I think I’m going to focus on getting in shape, losing weight, and curtailing those weekday glasses of wine before I install blackout curtains in the bedroom.


About leftbreast

I have had breast cancer. I was diagnosed at 47, and am now 49. I have finished "active treatment," two surgeries, chemo, radiation, monoclonal antibodies. These days, I only take a drug to suppress my uptake of estrogen, since my tumor was highly reactive to that hormone. I have been married to my husband Pete for 21 years. I have a stepdaughter, Maureen, 30, and a daughter, Erin, 10. I've been a freelance magazine journalist for 20-plus years, covering everything from Chinese foreign policy to Catholic nuns to endangered species. I have had a great life. I have lived in Asia and all over the United States. I have spent nights with tree-sitters in Oregon and with astronomers at the Mauna Kea observatory in Hawaii. I've been to a cocktail party on the poopdeck of a British destroyer docked in Shanghai. I've taken the bus to Tibet, and tramped through the cloud forests of Panama with biologists. A magazine sent me on a raft trip down the Colorado through the Grand Canyon; another sent me to cooking school for a week. I have spent time with celebrities, presidents and heroin dealers. I love my work. I have a loving, supportive family and more friends than I probably deserve. I have had the space and time to camp, ski, cycle, garden, cook and spoil my pets (an Australian shepherd, a German shepherd and a tabby cat). If it all ended tomorrow, I would have to say that it has been a really, really good ride. When I was in thick of treatment, I was simply fighting for more time. Now, I'm trying to connect the experience of cancer with the rest of my life, with the time that's been won. I hope the cancer never comes back, but if it does, I'll be ready. That's what this blog is about.
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1 Response to Afraid of our shadows?

  1. Hilda says:

    Heather, thank you for this rational, coherent analysis of a somewhat ridiculous study and an alarmist blog post over at

    I had the same thought — how do we know that the melatonin dip isn’t CAUSED BY having breast cancer, or going thru chemotherapy? Why would we automatically assume it’s instead working the other way and causing cancer?

    And it’s worth saying again: Correlation does not equal causation.

    Researchers, please stop telling women things like “you can reduce your breast cancer risk by wearing a sleep mask.” It isn’t helpful.

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