In the summer in Boston, the shortest night gets down to under nine hours, whereas winter nights are upwards of fifteen hours.
If we were alive before blackout shades and sleep masks, the duration of evening would effect our sleeping patterns, no?
During the winter, you might go to bed early because the sun sets early, plus it's cold and you'd want to get under a blanket with your warm cave-mate. In the summer, you'd stay awake longer with the longer days, and the rising sun would wake you up after a slumber of perhaps under eight hours.
So dual questions here:
Sleep hygiene be damned! I don't think that uniform bedtimes match naturally ebbing and flowing sunrises/sunsets, although they certainly do match modern work schedules :(
A scientist named Thomas A. Wehr did research in the 1990s to answer this question. He found that under natural conditions, sleep patterns change as night grows longer, but not in the way you imagine.
Wehr discovered that under simulated natural conditions, as night becomes longer, the amount of sleep increases (as you suggest), but sleep also becomes biphasic (also known as bimodal). That means we sleep for a few hours, then wake for a couple of hours, then sleep again for a few hours. In other words, during long nights, people naturally wake in the middle of the night and stay up for a few hours before going back to sleep.
Biphasic sleep is the normal pattern for many animals, and people used to sleep that way in Europe until a few hundred years ago. We know this about Europe from the work of an historian named A. Roger Ekirch. He discovered that European languages used to have terms for the two periods of sleep. In English, the first period of sleep was called "dead sleep" or "first sleep." The second period was called "morning sleep" or "second sleep." These terms were ordinary parts of our language until the industrial revolution, when artificial lighting changed the sleep-wake cycle.
Here is a link to Wehr's original paper on this subject:
Wehr TA. In short photoperiods, human sleep is biphasic. J Sleep Res. 1992 Jun;1(2):103-107.
And here is Ekirch's book about European sleep before the Industrial Revolution:
Ekirch, A. Roger. At Days Close: Night in Times Past (2005). Norton.
Here's an article by Ekirch which formed the basis of his book, and which is availble on the web for free:
Ekirch, A. Roger. Sleep we have lost: pre-industrial slumber in the British Isles. American Historial Review2001 April;106(2).
Well, Boston is one thing, equatorial Africa is another. And India is yet another (if I may make assumptions from your name and your photograph).
The shortest day in New Delhi, late December: 10 hours, 22 minutes. The longest day, late June: 13:55.
The shortest day in Kolkata, late December: 10:45. The longest day, late June: 13:31.
The shortest day in Chennai (Madras), late December: 11:20. The longest day, late June: 12:55.
The shortest day on the equator, late December: 12 hours. The longest day, late June: 12 hours. (More or less.)
There's my answer. I stopped reading Lights Out: Sleep, Sugar, and Survival because it seemed like a central assumption for the authors was that changes in light and climate from season to season were written into our genes, in a very deep way. But the most important thing is that we have no idea about the extent to which things like this are set in to our bodies, genetically or "epigenetically": if it's only been 60,000-100,000 years since most of us left Africa, then is that long enough to make adherence to seasonal patterns central to my health? I have no idea. I'm not claiming you're making the assumption as problematically as the authors of Lights Out are. But if I were someone of equatorial African origin reading that book I would definitely be scratching my head, wondering if the ideas in it applied to me or not.
im in the boston area, too (cape ann) and winter is hard on me and everyone i know for those reasons. leaving for work in the dark and coming home in the dark is not good for ones mental health and it doesnt take an expert to tell me that.
my kids for some ungodly reason both wake up at 5am. this is often 2+ hours before sunrise in winter, and i want to curl up and die. i cannot for the life of me figure out why they wake up before the sky is even gray, with blackout curtains and white noise int heir rooms, at the SAME. DAMN. TIME. EVER. DAY. when they do it in summer, its much easier for my husband and i to get up with them, but in winter its torture. they also both tend to fall apart and go to bed at 6:30pm in winter, and closer to 8pm in summer. i often wonder if their sleep patterns are more "natural", and (i have such limited experience with this) im pretty sure that the circadian rhythms of young kiddos are more primitive than our own which are so subject to habit and work schedules.
i FEEL like i want to sleep in in the winter, but i feel that to an extent all the time. i FEEL like i want to go to bed earlier when its dark out earlier, but i tend to wrap myself in cashmere and force myself to stay up for true blood. i dont know- i think our sleep habits are so damaged by work, computers, lights, that it would take months of living without electricity out in the wilderness all alone before we could figure out what we should be doing.
the climate here at this longitude is certainly not conducive to long winter nights as there isnt much work to do as far as food gathering, i would imagine. it would make sense that people would conserve energy in the winter until fairly recently when we got all these fancy grocery stores and indoor heat.
This is a very good question, Kamal!
It made me think of http://www.ted.com/talks/jessa_gamble_how_to_sleep.html It's short and a must view.
And it reminded me that I want to read Jessa Gamble's forthcoming book http://www.amazon.ca/Siesta-Midnight-Sun-Jessa-Gamble/dp/0670065110
Also read "Toward a comparative developmental ecology of human sleep" (2002). http://webdrive.service.emory.edu/groups/research/lchb/PUBLICATIONS%20Worthman/PUBLICATIONS%20CMW%202002/Ecology%20of%20Human%20sleep.pdf It's long but fascinating. There are some major, major differences in how different groups of humans sleep.
I'm writing to add that when I've briefly lived in a village in Western Africa, sleep schedules were all dictated by daylight. It was pretty awesome actually. There really wasn't an option to stay up with lights, because there were just a few solar powered batteries in the village. It was so refreshing not to be bound by the clock.
I have long thought the same thing, Kamal, and agree with you 100%! I get the feeling that it is our unnatural life-styles that are actually at the root of "Seasonal Affective Disorder" and the depression that so many people...including myself...get at the holidays. p.s. I absolutely hate street lights.
My personal feelings in the winter are that if it's dark out I should be sleeping (well that's how my body feels at least). To be honest, every chance I get in the winter to sleep while it's dark out, I take it. I'm unfortunately always up before the sun rises due to my job, but on weekends I'm up with the sun rising in my window.
I'm sure the lack of sunlight in my cave at work doesn't help much either. The only sun I get is if I can sit outside for lunch or if it is light on the way home. Basically I stay up with the sun in the summer and attempt to go to bed with the lack of it in the winter.
Not scientific but it's what I do. Even when I was in college it's what my body always told me, though obviously then and now other commitments don't allow my body to get all the sleep it thinks it needs.
First Paleo Winter 4 Answers