There is plenty on the internet for how to adjust to a higher altitude and how long it takes. But I live at a higher altitude. When I go down to sea level I could run for miles without hitting the wall, and drink like a fish without getting drunk. But how long could I stay at sea level before my “normal” would reset from 6000 feet to sea level and I’d have to readjust when I went back home? Looks to me like you need to spend around 4 days at altitude to get acclimated enough to push yourself physically, 45 days at altitude to get good and acclimated, so then, how long does it last?
When you go to altitude your body adjusts by producing more red blood cells. Those extra red blood cells last about as long as it took to create them. So if you go to altitude for 2 weeks the effects would last about two weeks at low altitude. If I recall correctly the maximum time is roughly 6 weeks. The adjustment varies depending on how long you spend at altitude.
For those who live at high altitude there’s a maximum amount of time before the effects wear off at low altitude. I’ll have to look it up when I get in front of a computer.
There haven’t been as many studies of people who live at altitude going back to sea level, but what has been studied shows you start to lose blood volume in as little as two weeks. So you start losing some of your benefits from acclimatization fairly quickly. You’ll probably lose the majority of the acclimatization benefits by 6 weeks, roughly the same time as it takes to fully acclimatize when coming up to altitude from sea level. This is even after living at altitude your entire life.
The exception would be if you were a Sherpa or someone from the Andes. These ethnic groups have physiological differences that are permanent adaptations to altitude and don’t go away when they travel to sea level.
Anecdotal – My Wife races IronMans. Fulls and halfs. We live at 11,200. She trains around 9-10,000 feet. She doesn’t feel she is any faster/more stamina at sea level. From what I have witnessed, I have to agree.
I guess for her, O2 isn’t an issue at all. Up at altitude, her blood O2 concentration is at 98-99%.
From my personal experience, when I was living in Montana and occasionally coming back to visit family, it was somewhere in the general range of two weeks before I started noticing the effects when I went back to Montana. Of course, it also depends on factors like how much exercise I got during that time (usually not much, because it was on vacations).
Red blood cells have a lifespan of about 3 months. So for that part of acclimatization, you’d expect that no longer than 3 months after you moved to sea level all the old high altitude RBC would be dead.
So the remaining question is how long after you arrived at sea level would you still be producing RBCs in high altitude quantities. After that time has passed and your production declined to sea level normal, 3 months later all the excess RBCs would have washed out.
Keep in mind that acclimatization is far, far more than just producing more RBCs.
Hypoxic ventilatory response is one critical change. Minute ventilation goes up, alveolar CO2 goes down, and less CO2 means there’s more O2 in the alveoli. And as the blood gets more alkaline due to CO2 washout, renal compensation mechanisms kick in to minimize that effect. This means the kidneys are excreting more fluids.
Circulatory changes occur (in part due to increased fluid loss thru the kidneys) and cardiac output goes up. Cerebral vessels expand in the face of low oxygen, but may end up constricting if CO2 is washed out excessively. A form of balance is eventually achieved between dilation and constriction, to maximize oxygenation of the brain.
Pulmonary vasculature starts shunting more blood to less ventilated sections of the lungs, to maximize oxygen absorption. Capillary beds expand in tissues to improve oxygen delivery.
Acclimatization takes place on the cellular level too, improving oxidative metabolism efficiency.
Those changes take from hours to months to occur. And there’s not been a lot of study as to how quickly those adaptations are lost when one goes to lower altitude.
Bottom line: It’s complicated, and results vary widely from individual to individual.
More detailed descriptions about what happens during acclimatization, etc can be found in this book: West JB, Schoene RB, Milledge JS. High Altitude Medicine and Physiology, Hodder Arnold, London 2007.
So how do their bodies react when they are at sea level ?
Okay, I read the thread title as,“Attitude adjustment, how long does it last?”
My answer: almost never.
Carry on.
I mis-read the title as being 'attitude adjustment". I’ve known some who had their attitudes adjusted for life, (which turned out to not be very long, for some).
I got latitude adjustment … couple hundred generations.
Cardiorespiratory response to exercise in elite Sherpa climbers transferred to sea level - PubMed - Anyone have access to PubMed?
Thank you. I have avoided this thread for this reason. 
I need some new reading glasses.
I do agree with the acclimatization. I have gone from 15,000 feet back to about 4’000 and back again within 2 days. I was not a happy camper.