0 Brubaker, Patricia L. 2005 Diabetes Care 28 2563-2572 Regular exercise is encouraged in patients with type 1 diabetes (1) and, indeed, the American Diabetes Association states that people with type 1 diabetes should be able to partake "in all forms of physical activity consistent with an individual’s desires and goals" (2). In keeping with this philosophy, increasing numbers of people with type 1 diabetes now participate in extreme forms of physical activity, including high-altitude trekking and mountain climbing, as evidenced by several recent publications (3–10). However, exercise at altitude imposes a number of unique challenges for people with type 1 diabetes, including impairment in glycemic control, and it may have negative consequences in patients with complications. This review will consider what is known about the impact of altitude on individuals with type 1 diabetes, and it will propose strategies for dealing with these challenges. For the purposes of this review, high altitude is defined as 3,000–5,000 m (10,000–16,000 ft) and extreme altitude as >5,000 m. As barometric pressure decreases linearly with increasing altitude, inspired PO2 at the summit of Mount Everest (8,848 m) is <30% of that at sea level (11). Acclimatization refers to the physiological changes that occur consequent to prolonged exposure to the hypoxia and low barometric pressure of altitude, and it includes hyperventilation, with the resultant respiratory alkalosis being reduced over time by compensatory renal bicarbonate excretion. Although erythrocyte levels also increase, this occurs much more slowly, over the course of several weeks (11). It is also important to note that acclimatization does not imply normalization because, despite continued hyperventilation, alveolar PO2 levels remain well below that at sea level even in fully acclimatized individuals. http://care.diabetesjournals.org/cgi/content/full/28/10/2563