As a dietary supplement, the U.S. recommended daily allowance of vitamin B-1, or thiamine, is 1.2 milligrams for males 14 years and older and 1.1 milligrams for women over 18 years old, according to MedlinePlus. In specialized cases, health care providers may recommend larger doses.
For a mild thiamine deficiency, a daily dose of 5 to 30 milligrams is common, with a dose of up to 300 milligrams prescribed for severe deficiencies, states MedlinePlus. The recommended daily allowance of vitamin B-1 for pregnant women is 1.4 milligrams, with 1.5 milligrams the usual dose for women who are breast feeding. To help reduce the chance of cataracts forming, doctors recommend a daily intake of 10 milligrams.