Effect of Reduced Protein Intake on Nitrogen Loss from the Human Integument

Abstract

Nitrogen losses from the integument were studied in 20 male subjects ranging in age from 20 to 39 years under nonsweating, resting conditions in conjunction with a nitrogen balance study designed to ascertain minimal protein requirements for man. Subjects wore long underwear for repeated collection periods of 3 or 6 days. Hair and beard were weighed and nail growth was measured from serial nail markings. Nitrogen in bath and laundry water ranged from 59 to 204 mg/day with a mean of 119 mg for subjects on a control diet containing 12.3 g of nitrogen. When the subjects were given 0.6 or 3.8 g of nitrogen daily there was a significant decrease in the amount of nitrogen lost in the dermal excretions. Blood urea nitrogen and dermal excretion of nitrogen were positively correlated. Varying the levels of nitrogen intake did not affect the rate of hair and beard growth. The nails grew an average of 0.093 mm/day and average total head hair growth was 160 mg/day. An average daily loss of 24 mg of nitrogen is attributed to head hair and nail replacement.