Night Light/Cancer Correlation

On Dr. Andrew Weil's site this morning, he answered a question from a reader on the possible connection between exposure to light during night hours and breast cancer.

A link between light at night and breast cancer is not yet proven, but there is a growing body of evidence for the correlation. A 2001 study from the Fred Hutchinson Cancer Research Center found that women in Seattle who work the graveyard shift face up to 60 percent increased risk of breast cancer. Other studies have shown a similar pattern. And the risk of breast cancer is up to five times higher in industrialized nations (where exposure to nighttime illumination is more common) than it is in undeveloped countries. About half of those breast cancers cannot be accounted for by conventional risk factors.

So what's going on?

Back in 1987, a researcher named Richard Stevens, then at Pacific Northwest Laboratories in Richland, Washington, hypothesized that even brief exposure to nighttime illumination suppressed the pineal gland's production of melatonin, a neurotransmitter with strong anti-cancer properties.

Recently, that hypothesis came closer to confirmation. In April, I had the privilege of listening to a presentation by David E. Blask of the Bassett Research Institute in Cooperstown, NY. In research published in 2005, he found that human breast-cancer tumors grafted to rats grew more quickly in the presence of melatonin-depleted blood. The growth was fueled by rapid uptake of linoleic acid, a proinflammatory fat that's abundant in processed food, especially fried snack foods.

So far, light at night has not been linked to other kinds of cancers, perhaps because melatonin suppression boosts estrogen production by the ovaries, which in turn can support cancerous cells in a woman's breast. In other words, diminished nighttime melatonin production may boost breast cancer risk by two different mechanisms: speeding cancer cells' linoleic acid uptake and boosting estrogen levels. But I would not be surprised if light at night is eventually correlated with other cancers as well.

Read the rest here.

Personally, it feels to me as though every time I turn around there's yet another thing I do that can cause cancer, and I become frustrated with the information overload. What's especially maddening is that sometimes the warnings come based on one solitary study. Nevertheless, I thought it worthwhile to pass the information along as three studies now seem to indicate a possible correlation/causation. There. You have the information. Research it more, if you are interested, and decide for yourselves.