Denver, often called the “Mile High City,” sits at 5,280 feet above sea level. Moving to or visiting this altitude requires acclimation, a physiological process where the body adjusts to the environment. This adjustment is necessary because the lower barometric pressure means each breath contains fewer oxygen molecules than at sea level. The time it takes to acclimate fully varies, but the body begins its work immediately upon arrival.
What Happens When You Arrive
When a person arrives from a lower elevation, the sudden reduction in available oxygen triggers an immediate response. This phenomenon is called hypobaric hypoxia, a state of reduced oxygen availability due to lower atmospheric pressure. To compensate, the body instinctively increases the rate and depth of breathing (hyperventilation) to draw in more oxygen.
The initial physical strain can lead to mild, temporary symptoms grouped under acute mountain sickness (AMS). Common signs appear within the first 6 to 24 hours, including a mild headache, tiredness, and lightheadedness. People may also become winded faster during light physical activity, such as climbing stairs. These discomforts signal that the body is working harder to maintain oxygen saturation.
The Typical Acclimation Timeline
For most visitors, the most noticeable acute symptoms peak within the first 24 to 48 hours and then begin to subside. During this initial phase, the body focuses on short-term fixes by altering breathing and heart rates to maximize oxygen intake and circulation. This rapid response allows many travelers to feel significantly better and functional after two days.
The mid-term adjustment extends from the third day up to about seven days after arrival. Within this window, the body begins more significant physiological changes, such as stabilizing fluid balance and adjusting blood chemistry. Most practical acclimation for a typical vacation occurs during these first three to five days, allowing for near-normal activity levels.
True, complete adaptation is a much longer process, primarily involving the production of additional red blood cells and increased capillary density. This deeper change can take several weeks to months, with a full adjustment often taking about three weeks. This full adaptation is generally only necessary for new residents or individuals planning sustained, strenuous activity.
Strategies for a Smoother Adjustment
Aggressive hydration is one of the most effective methods for mitigating the effects of a higher elevation. The air is often drier than at sea level, and the body loses fluid faster through increased respiration and urination, making it necessary to drink significantly more water than usual. Maintaining proper fluid balance helps the blood efficiently transport oxygen throughout the body.
It is wise to avoid strenuous activity for the first day or two, giving the body time to manage the initial oxygen deficit without added stress. Instead, opt for light sightseeing or short walks, and gradually increase the intensity of exercise only as you feel comfortable. Pacing your activity level prevents overexertion, which can significantly worsen the symptoms of mild altitude sickness.
Limiting or entirely avoiding alcohol and caffeine during the initial 48 hours can also smooth the transition. Both substances can act as diuretics, accelerating dehydration and compounding the fluid loss caused by the dry, thin air. Prioritizing rest and sufficient sleep is equally important, as the body uses this time to recover and manage the metabolic changes necessary for acclimation. If symptoms like severe shortness of breath, confusion, or persistent vomiting occur, these are signs of more serious altitude sickness, and medical attention should be sought immediately.