Vitamin B1 (also known as thiamine) deficiency causes the disease beri-beri, which is characterised by loss of appetite, retarded growth, and nerve degeneration. Among the other options: deficiency of vitamin B2 (riboflavin) causes cheilosis (fissuring at corners of mouth and lips), deficiency of vitamin B6 (pyridoxine) causes convulsions, and vitamin E deficiency can lead to sterility and muscular weakness.