The tide of enzymes and hormones produced in our body surges and subsides throughout the day in rhythm with these molecular signals. Because our internal rhythm runs on a cycle that is slightly longer than the solar day, the master clock is like an orchestra conductor, prompting the entire body to stay in step with the 24-hour solar cycle.
Riding the circadian cycle
Modern life, with artificial lighting that permits people to work or play all night long, makes it harder to maintain healthy circadian cycles. But people disrupt these rhythms at their peril, Sassone-Corsi says. Women who regularly work night shifts, like nurses, “have something like three to four times more chance to get breast cancer,” he observes.
Mariana Figueiro likes to say that people are natural “blue sky detectors.” We need a certain level of daylight, ideally soon after sunrise, to stay in sync, she says. The light needed to stimulate our circadian rhythms is more intense than that required for vision, which is why it is important to be outdoors.
“The circadian system is looking at the contrast between dark and light,” she says. The best light to stimulate the system during the daytime is in the blue wavelengths with at least an hour of exposure per day.
Seeing the light of day
But for older people, in addition to physiological changes, “you have behavioral change,” Figueiro says. “Older people don’t go out as often. They tend to stay indoors.” While taking a daily morning walk is ideal, an alternative is to improve indoor lighting. “It’s important to have higher lighting levels—bluish-white daytime lighting and a lower, warmer, incandescent spectrum at night,” she says.
Blue light at the right time of day—around sunrise—suppresses melatonin and tells the body it is daytime, Figueiro says, and the light should be at least eight times more intense than the lighting typically found in nursing homes. People should avoid blue light in the evening, when the body is supposed to be making more melatonin in preparation for sleep.
Figueiro is also conducting preliminary studies using light to help people with early-onset Alzheimer’s disease, which is frequently characterized by fragmented sleep. “It’s one of the biggest reasons they’re institutionalized,” she says.
As for Katherine Closson, she admits that she doesn’t get outdoors as often she used to since developing a hip infection a couple of years ago. But she has kept the bright blue-white bulbs she was given for the circadian study. “I’m as happy as a lark,” she says.
Michael Haederle is a freelance writer whose work has appeared in People, the New York Times and the Los Angeles Times.