What’s in a Color? The Unique Human Health Effects of Blue Light

Abstract

In 1958, J. Woodland Hastings and Beatrice M. Sweeney tested the ability of different wavelengths of light—corresponding to different colors—to shift the circadian rhythm in the photosynthetic marine dinoflagellate Gonyaulax polyedra. The greatest power to reset the organism’s daily meter lay in the blues, with a precipitous decline into the greens and a modest boost in the reds. Hastings and Sweeney’s paper, published in the December 1958 Biological Bulletin, gathered dust for decades. No one thought these findings might hold any relevance for humans, whose circadian rhythms were then widely believed to be relatively insensitive to light. But scientific discoveries in the past two decades have changed all that. Not only does light reset the human circadian rhythm, but the same blue light that has the strongest impact on dinoflagellates has equal power to reset our own clocks—although most visible wavelengths can reset the clock, the blues do the job with the greatest efficiency. Now researchers are finding increasingly that an out-of-phase circadian rhythm is a health hazard. “Maintaining synchronized circadian rhythms is important to health and well-being,” says Dieter Kunz, director of the Sleep Research and Clinical Chronobiology Research Group at Charite–Universitatsmedizin Berlin. “A growing body of evidence suggests that a desynchronization of circadian rhythms may play a role in various tumoral diseases, diabetes, obesity, and depression.” Shift workers, whom Kunz calls “a model for internal desynchronization,” are known to experience increased morbidity and mortality for a number of diseases, including cardiovascular disorders and cancer. In fact, in 2007, the World Health Organization decreed that shift work is a risk factor for breast cancer, and on that basis, in 2009, the Danish government began compensating some female shift workers with breast cancer. At the same time, researchers have repeatedly shown that bright white light has the power to mitigate depression and other maladies of mood. An emergent recent literature suggests that blue light may be particularly potent for such applications.