I always get a little groggy when flying cross-country. My circadian clock gets knocked off it's firm pedestal and starts jumping rope inside my head and doing handsprings through my body. To begin with, light set this clock. And I smash it by leaving California at 10AM and chasing the darkness until I arrive on the east coast 4 hours later at night.
Ugh. My rods and cones hurt.
Until recently, the color-seeing, bright-light-active cone structure in the eye was the main gateway for programming (and throwing off) the circadian rhythms that settle our body into a pattern of sleep/wake and hormone and hunger ups and downs. But, Johns Hopkins biologist Samer Hattar says--we can't count out our black-and-white-seeing rods. No one is sure exactly how circadian clocks establish the rhythm of your body's function. But, we can at least do experiments that eliminate rod or cone function in our eyes and see if it affects our (or in this case, a mouse's) circadian clock as effectively as a transatlantic flight.
Scientists genetically modified one group of mice to have only cone function (color vision, bright light), and another group of mice to have only rod function (b & w vision, low light). The first group loved Wizard of Oz. The second group never left Kansas. Both groups were exposed to varying degrees of light at varying times of day, and then ushered onto a hamster wheel to measure the amount of energy they had at morning, noon, and night compared to normal. It turns out, cone-free mice were exhausted by exposure to both dim and bright light at the wrong time, proving rods are involved in setting circadian rhythms in both dim light and in bright light.
The two main conclusions from the study:
"One is that it had previously been thought that circadian rhythms could only be set at relatively bright light intensities, and that didn't turn out to be the case," he explained. "And two, we knew going in that rods 'bleach,' or become ineffective, when exposed to very bright light, so it was thought that rods couldn't be involved in setting our clocks at all in intense light. But they are."
So circadian rhythms can be set in low light. With rods. But, they're also set in bright light, too.
The authors suggest--it's all about getting the most contrast you can get from day to night. Lots of bright light during the day. Minimal low light at night. So, the low light from a nightlight could disrupt your circadian rhythms (if you don't get much bright light during the day either), and flying east could also have a disruptive effect, limiting your bright daylight exposure by literally shortening your day. Soaking up low light all day in an office building and all night at home can creating the same raucous of symptoms like headache and fatigue.
Finally. Someone proved why it's bad to stuff yourself in a cubicle your whole life....or bad to stuff mice in a cubicle their whole lives. Testing humans would be the next step. Then, if the same results result, the government could institute things like: daily walks outside their nursing home for the elderly, mandatory 10 minutes out front of the law firm at lunch, and pitch darkness on the red-eye flight. Stuff that we kind-of already know works anyway.
Altimus CM, Güler AD, Alam NM, Arman AC, Prusky GT, Sampath AP, & Hattar S (2010). Rod photoreceptors drive circadian photoentrainment across a wide range of light intensities. Nature neuroscience, 13 (9), 1107-12 PMID: 20711184
