Environmental and physical stress and nutrient requirements.

When faced with hot, cold, or high-altitude environments, humans can either modify the microenvironment to fit human physiology, adapt their physiology to fit the environment, or use a combination of these two tactics. Metabolic adaptations to heat, cold, and high-altitude exposure may, in some instances, be accompanied by changes in nutrient requirements. Energy expenditure is increased in all three environments. B-vitamin cofactor requirements increase in proportion to energy expenditure (oxidation of fat and carbohydrate). Increased B-vitamin nutrient requirements are usually adequately met by an increased consumption of the diet to meet energy requirements. Other nutrients such as iron may be required in greater amounts to meet the altitude-induced hematopoietic response in females. Additional quantities of vitamins and minerals with antioxidant properties may be beneficial to reduce the increased oxidative stress associated with work in heat, cold, or high-altitude outdoor environments.