Our sleep num­ber isn’t nat­u­rally 8, study sug­gests

In re­mote ar­eas, hunter-gath­er­ers are re­freshed on less

The Washington Post Sunday - - POLITICS & THE NATION - BY ARI­ANA EUN­JUNG CHA ari­ana.cha@wash­post.com More at wash­ing­ton­post.com/ blogs/to-your-health

Mod­ern life’s sleep trou­bles — in­clud­ing the chronic, blearyeyed state that many of us live in — have long been blamed on our in­dus­trial so­ci­ety. The city lights, long work hours, com­mutes, caf­feine, the In­ter­net.

When talk­ing about the mis­er­able state of our abil­ity to get enough rest, sleep re­searchers have had a ten­dency to harken back to a sim­pler time when hu­mans were able to fully recharge by sleep­ing and wak­ing to the rhythms of the sun.

That may not be quite right. It now ap­pears that our an­ces­tors may not have been get­ting the eight hours of sleep rec­om­mended by doc­tors, either.

In an in­trigu­ing study pub­lished in the jour­nal Cur­rent Bi­ol­ogy, re­searchers trav­eled to re­mote ar­eas of the planet to scru­ti­nize the sleep pat­terns of some of the world’s last re­main­ing hunter-gath­er­ers — the Hadza of Tan­za­nia, the San of Namibia and the Tsi­mane of Bo­livia. Cut off from elec­tric­ity, me­dia and other dis­trac­tions, th­ese prein­dus­trial so­ci­eties are thought to ex­pe­ri­ence the same sort of nat­u­ral sleep that an­cient hu­mans en­joyed more than 10,000 years ago.

Lo­cated in a wood­land-sa­van­nah habi­tat 2 de­grees south of the equa­tor, the Hadza gather their wild foods each day. The San are not mi­gra­tory, but they in­ter­act very lit­tle with sur­round­ing vil­lages and live as hunter-gath­er­ers.

The Tsi­mane, who live close to the Maniqui River, are hunter hor­ti­cul­tural i st.

Us­ing Ac­ti­watch 2 de­vices (a kind of a souped-up, med­i­cal­grade Fit­bit for sleep), re­searchers recorded the sleep­ing habits of 94 tribe mem­bers and ended up col­lect­ing data rep­re­sent­ing 1,165 days.

What they found was a strik­ing uni­for­mity in sub­jects’ sleep pat­terns, de­spite the geo­graphic iso­la­tion. On av­er­age, all three groups slept a lit­tle less than 6.5 hours a night, did not take naps and did not go to sleep when it got dark. Like many of us, the Hadza, San and Tsi­mane spent more time in bed — for a to­tal of 6.9 to 8.5 hours — than ac­tu­ally sleep­ing. That com­putes to a sleep ef­fi­ciency of 81 to 86 per­cent — very sim­i­lar to to­day’s in­dus­trial pop­u­la­tions.

The study’s co-author, Jerome Siegel, di­rec­tor of the Univer­sity of Cal­i­for­nia at Los An­ge­les’s Cen­ter for Sleep Re­search, and his col­leagues ex­plained that this sug­gests that sleep may not be en­vi­ron­men­tal or cul­tural, but “cen­tral to the phys­i­ol­ogy of hu­mans” liv­ing in the trop­i­cal lat­i­tudes where our species evolved.

“The short sleep in th­ese pop­u­la­tions chal­lenges the be­lief that sleep has been greatly re­duced in the ‘mod­ern world,’ ’’ Siegel said in a state­ment. “This has im­por­tant im­pli­ca­tions for the idea that we need to take sleep­ing pills be­cause sleep has been re­duced from its nat­u­ral level by the wide­spread use of elec­tric­ity, TV, the In­ter­net, and so on.”

The find­ings call into ques­tion the un­told mil­lions of dol­lars that have been spent on re­search that tries to get to the bot­tom of why “short” sleepers get only about six hours of sleep a night and the idea that lack of sleep might be a big rea­son that obe­sity, mood dis­or­ders, and other phys­i­cal and men­tal ail­ments have surged in re­cent decades.

Our ideas about nap­ping may need re­vis­ing, too.

Sci­en­tists have long doc­u­mented that peo­ple have a ten­dency to “crash” in en­ergy in the midafter­noon, and some have spec­u­lated that it is be­cause we have man­aged to sup­press some in­nate need for a si­esta. The study pro­vides ev­i­dence that this is un­likely.

The data from the San in Namibia, for in­stance, showed no af­ter­noon naps dur­ing 210 days of record­ing in the win­ter and 10 naps in 364 days in the sum­mer. The find­ings were sim­i­lar for the other two tribes, sug­gest­ing that nap­ping is not re­ally a com­mon thing among hunter­gath­er­ers, either. At the high end, the re­searchers es­ti­mated that naps may have oc­curred on up to 7 per­cent of win­ter days and 22 per­cent of sum­mer days. The re­searchers noted that the de­vices they were us­ing were not great at pick­ing up naps of short du­ra­tions, so it was pos­si­ble that some of the study sub­jects were tak­ing power naps of less than 15 min­utes.

An­other fas­ci­nat­ing find­ing from the study had to do with the cir­ca­dian rhythms re­lated to sun­light. In­stead of go­ing to sleep right at dusk, the hunter­gath­er­ers were do­ing so an av­er­age of 2.5 and 4.4 hours af­ter sun­set — well af­ter dark­ness had fallen. All three tribes had small fires go­ing, but the light it­self was much lower than you might get from your av­er­age 60-watt bulb. They did, how­ever, have a ten­dency to wake up around sun­rise — an hour be­fore or an hour af­ter.

Siegel and his co-au­thors in­ves­ti­gated this fur­ther by look­ing into the sig­nif­i­cance of tem­per­a­ture, and found that it might play a big role. The re­search showed that “sleep in both the win­ter and sum­mer oc­curred dur­ing the pe­riod of de­creas­ing am­bi­ent tem­per­a­ture and that wake onset oc­curred near the nadir of the daily tem­per­a­ture rhythm,” they wrote.

It should be noted that the tribe mem­bers stud­ied are dif­fer­ent from your av­er­age Amer­i­can in a num­ber of re­spects.

Im­por­tantly, very few of the hunter-gath­er­ers suf­fer from chronic in­som­nia. There is no word for it in their lan­guages.

In in­ter­views with the re­searchers, con­ducted through in­ter­preters, 1.5 to 2.5 per­cent of the study sub­jects said that they had sleep onset or sleep main­te­nance prob­lems more than once a year, which is far lower than the 10 to 30 per­cent doc­u­mented in many coun­tries to­day. Siegel sug­gested that this may mean that “mim­ick­ing as­pects of the nat­u­ral en­vi­ron­ment” may be ef­fec­tive in treat­ing some sleep dis­or­ders.

The hunter-gath­er­ers are also much health­ier. Not a sin­gle one is obese, and the mean body mass in­dex read­ings among the tribes were be­tween 18.3 and 26.2, which is con­sid­ered quite slim. They also tend to have lower blood pres­sure, bet­ter heart con­di­tions and higher lev­els of phys­i­cal fit­ness.

Thus comes a crit­i­cal ques­tion. If we can­not blame the lack of sleep as caus­ing our col­lec­tive obe­sity, mood dis­or­ders and the like, could it be that the rea­son we feel so un­rested is be­cause of poor health?

On av­er­age, all three groups slept a lit­tle less than 6.5 hours a night and did not take naps.

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