The effect is so large, so easy to notice, it is enshrined in the word cold. We get far more colds and flu in the winter (“flu season”) than in the summer. In this excellent interview, epidemiologist Thomas Jefferson asks:
Why, for example, do we not get influenza in the summertime?
All of the possible explanations listed in this Wikipedia article assume that it is cold weather that makes flu more common in winter. However, an impressive 1981 study found that flu peaked during the light minimum, not the temperature minimum, contradicting all of these explanations.
My proposed explanation is that flu is less common in the summer because people sleep better during the summer. They sleep better in the summer because they get more morning light. More morning light causes your circadian system to have a greater amplitude, which means you sleep more deeply. Better sleep –> better immune function. When I started to sleep much better, I stopped getting noticeable colds and flu.
When I wrote my paper it was essentially impossible to test my idea. You need to measure a lot of sleep — and sleep scientists, intent on making it hard to do what they do, have made this nearly impossible. Perhaps it will soon be easier. To begin with, to test my idea you’d need to improve sleep somehow. To get more light exposure during winter is easy enough with a light box but measuring quality of sleep is much harder. Maybe FitBit (which will start shipping in a few months) will make this possible. I tried using SleepTracker to measure my sleep but after a few months I gave up. There were four big problems: 1. The interface didn’t work very well. It was often hard to get the data from the device into my computer. 2. The whole thing wasn’t designed to measure sleep, it was designed to wake you at a better time than you would wake up without it. 3. The way it measured sleep was a secret. 4. The output — the measure of sleep — was binary. All you were told was whether movement was above or below some threshold. And I had no idea how that threshold was determined.
Seth, John Cannell and several others published a paper recently arguing that variations in vitamin D levels are responsible for the seasonal nature of the flu. Interestingly enough, this follows both the light – not temperature – minimum, and immune system involvement. Here’s the abstract from PubMed (no link as it holds up the comment):
On the epidemiology of influenza.
Cannell JJ, Zasloff M, Garland CF, Scragg R, Giovannucci E.
Department of Psychiatry, Atascadero State Hospital, 10333 El Camino Real, Atascadero, CA 93423, USA. jcannell@ash.dmh.ca.gov
Comment in:
* Virol J. 2008;5:149.
The epidemiology of influenza swarms with incongruities, incongruities exhaustively detailed by the late British epidemiologist, Edgar Hope-Simpson. He was the first to propose a parsimonious theory explaining why influenza is, as Gregg said, “seemingly unmindful of traditional infectious disease behavioral patterns.” Recent discoveries indicate vitamin D upregulates the endogenous antibiotics of innate immunity and suggest that the incongruities explored by Hope-Simpson may be secondary to the epidemiology of vitamin D deficiency. We identify – and attempt to explain – nine influenza conundrums: (1) Why is influenza both seasonal and ubiquitous and where is the virus between epidemics? (2) Why are the epidemics so explosive? (3) Why do they end so abruptly? (4) What explains the frequent coincidental timing of epidemics in countries of similar latitude? (5) Why is the serial interval obscure? (6) Why is the secondary attack rate so low? (7) Why did epidemics in previous ages spread so rapidly, despite the lack of modern transport? (8) Why does experimental inoculation of seronegative humans fail to cause illness in all the volunteers? (9) Why has influenza mortality of the aged not declined as their vaccination rates increased? We review recent discoveries about vitamin D’s effects on innate immunity, human studies attempting sick-to-well transmission, naturalistic reports of human transmission, studies of serial interval, secondary attack rates, and relevant animal studies. We hypothesize that two factors explain the nine conundrums: vitamin D’s seasonal and population effects on innate immunity, and the presence of a subpopulation of “good infectors.” If true, our revision of Edgar Hope-Simpson’s theory has profound implications for the prevention of influenza.
You might be interested in the zeo sleep monitor. It estimates the amount of deep, light and rem sleep. It would be better if the data could be exported into a spreadsheet. it’s not perfect but I like it, I’ve been using it for a while.
It’s not perfect, but to measure quality of sleep, couldn’t you simply ask people how well they slept, how rested they felt in the morning, etc., and related that to whether they get the flu?
Yeah, I gotta say that it’s more likely that it’s Vitamin D than it is sleeping better. In fact, I know a lot of people who say they sleep better in the winter. (Talk about anecdotal data!)
And I think it’s actually different for different people. I have moderate Seasonal Affect Disorder (SAD), and I live in the Pacific NW, so winters are dark. I get better sleep if I use my bright “SAD” light in the evening. And that’s not uncommon. Bright morning light gives me more energy during the day, but doesn’t help me sleep better.
Vitamin D, however is a killer immune system booster…okay, bad choice of words. Since I moved to the NW, I’ve been taking 4-5000 units of D a day. And in three years, I have gotten only 1/2 of a cold that lasted for a couple of days. And I used to get 3-4 colds a year. I just felt another cold coming on in the afternoon, took 50,000 units of D3, and it was gone by the morning.
Cannell has posted a couple of suggestive epidemiological stories that seem to demonstrate that D protects against influenza.
All of this is not to say that sleep is not critical for immune system functioning. It is. But I think Vitamin D is more critical, and it contributes more to the immune system depression in the winter months.
Not to just be a ditto comment, but I think it’s the Vitamin D and not the sleep (or more the D than the sleep). Earlier this year my wife came down with the flu and I was initially not catching it from her — on the onset of a scratchy throat I immediately started megadosing Vitamin D3 — 20K IUs every day (I think I did 40K the first day, actually). My sore throat was gone in 24 hours and it never got worse. Prior to trying to megadose Vit D, once the sore throat hit, I’d automatically be in for a weeklong cold, at minimum. That it went away overnight on megadosing and never came back? Unprecedented.
I’ve since repeated that experiment with the same results *as has my wife.* There is a big connection, apparently, between Vit D and respiratory infections.
I have to point out an error in your post here as it pertains to Vit D. You wrote:
But on clicking through to the Wiki entry, I found this quote under “Mechanism for seasonal nature of influenza:”
In conclusion, vitamin D for the win!
Justin, thanks for the correction. Dennis, thanks for the link, I didn’t know about that paper. I hope it is Vitamin D, so much easier to control than sleep.
Here is an 2006 version of Cannell’s Vitamin D idea.
Desperately anecdotal, but another idea for the mix.
I live in Taiwan, and I’ve heard lack of sweating is a cause of colds. My home has no air con, so I sweat a lot in the long summer and mooch around in a sarong, but when the weather turns and I can start to wear real clothes I get my first cold of the season, which i then take to a sauna and sweat out.
just wanted to update/correct my previous comment on sleep tracking with Zeo and say that it now does support exporting the data to a spreadsheet. I noticed a big dip in REM and Deep sleep when I took an antibiotic a few months ago, pretty cool.
here is a link to the zeo data export doc https://mysleep.myzeo.com/export/Export%20Data%20Help%20Sheet.pdf