. (1971). Brit. J. industr. Med., 28, 246-258. Nutritional and environmental studies on an ocean-going oil tanker. 2. Heat acclimatization and nutrient balances. On the oil tanker S.S. Esso Newcastle, metabolic balances were investigated in three medical students and three working members of the crew during three-day experiments conducted when the ship was located in Biscay, the South Atlantic, and the Persian Gulf. Information was sought on the possible changes in nutrient requirements and the significance of the losses of nutrients in sweat when the subjects becarne acclimatized to heat. Physiological parameters of acclimatization were measured on each subject by controlled hyperthermia using a heated test-bed. Details are also given of the procedures devised for measuring the daily intake and loss of nutrients in metabolic balance studies on working subjects.The intakes of water, sodium (including salt supplements), potassium, nitrogen, and iron provided by the ship's diet were found to be adequate, or more than adequate, during the outward voyage to the Persian Gulf. In two crew subjects who worked in the engine room, there was a trend to more positive salt and water balance with sweat losses of 3 to 4 litres per day in the Persian Gulf, but not in the three students who, though artificially acclimatized, were seldom exposed to hot working conditions. Sweat concentrations of sodium, potassium, and nitrogen were related to the rate of 24-hour sweat loss but were not altered by heat acclimatization. In the environmental and dietary conditions on board, the effect of daily sweat losses of potassium, nitrogen, and iron on the respective balances was found to be insignificant.The urinary output of 17-OH corticosteroids increased slightly in mid-voyage in the students but was not raised in either students or crew in the Persian Gulf. There was evidence of temporary increases in plasma cortisol accompanied by negative nitrogen and potassium balances when unacclimatized crew members were exposed to heat stress at the start of the voyage.The investigation of human dietary requirements in status of service personnel in the tropics (Mitchell hot climates has had a long, if hesitant, history. The and Edman, 1951), and, more recently, interest in impetus for such studies has often come from the the comparative aspects has been stimulated by the need for more precise information on the nutritional International Biological Programme (Weiner, 1969).
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