Left-sided Cancer: Blame your bed and TV?

R. Douglas Fields in Scientific American:

Curiously, the cancer rate is 10 percent higher in the left breast than in the right. This left-side bias holds true for both men and women and it also applies to the skin cancer melanoma. Researchers Örjan Hallberg of Hallberg Independent Research in Sweden and Ollie Johansson of The Karolinska Institute in Sweden, writing in the June issue of the journal Pathophysiology, suggest a surprising explanation that not only points to a common cause for both cancers, it may change your sleeping habits.

For unknown reasons the rates of breast cancer and melanoma have both increased steadily in the last 30 years. Exposure to the sun elevates the risk of melanoma, but the sun’s intensity has not changed in the last three decades. Stranger still, melanoma most commonly affects the hip, thighs and trunk, which are areas of the body protected from the sun. What is responsible for the left-side dominance and increasing incidence of these cancers?

An intriguing clue comes from the Far East. In Japan there is no correlation between the rates of melanoma and breast cancer as there is in the West, and there is no left-side prevalence for either disease. Moreover, the rate of breast cancer in Japan is significantly lower than in the West; only 3 percent of what is seen in Sweden, for example. The rate of prostate cancer in Japan is only 10 percent of that in the U.K. and U.S.

The researchers suggest an explanation based on differences in sleeping habits in Japan and Western countries. Previous research has shown that both men and women prefer to sleep on their right sides. The reasons for this general preference are unclear, but sleeping on the right side may reduce the weight stress on the heart, and the heartbeat is not as loud as when sleeping on the left. Still, there is no reason to suspect that people in Japan sleep in positions that are any different from those in the West. The beds in Japan, however, are different. The futons used for sleeping in Japan are mattresses placed directly on the bedroom floor, in contrast to the elevated box springs and mattress of beds used in the West. A link between bedroom furniture and cancer seems absurd, but this, the researchers conclude, is the answer.

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