High altitude deadaptation affects the health of population returned to the plain. We examined major physiological functions in 348 healthy control subjects and 626 Qinghai-Tibet railway construction workers who returned to the plain from the Qinghai-Tibet plateau. Blood indices, such as hemoglobin, hematocrit, mean corpuscular volume, mean corpuscular hemoglobin concentration and platelet larger cell ratio, of the returned group that had stayed at high altitude more than 3 years were significantly higher than those of the control group. Red blood cell distribution width and platelet were significantly lower in the returned group than in the control group. Compared to the control group, five years after returning to the plain, the returned group had higher mean corpuscular hemoglobin and lower red blood cell distribution width. Detection rate of hypotension and low pulse pressure were significantly higher in the returned group than in the control group at 20 months after the return, and cardiothoracic ratio was significantly higher in the returned group than in the control group at 40 months after the return. Short-term memory function was significantly lower in the returned group than in the control group. Total triiodothyronine and thyroid-stimulating hormone were significantly lower, but total thyroxine and free triiodothyronine were significantly higher in the returned group than in the control group. Sex hormones level returned to normal level in the returned group. Superoxide dismutase was significantly higher and malondialdehyde was significantly lower in the returned group than in the control group. Fatty acid binding protein was significantly higher in the returned group than in the control group, and this difference maintained with time after the return. We conclude that physiological functions of most organs in returned population after exposed to high altitude can not be completely restored to the normal level in a short period of time.

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