The recommended daily allowance for vitamin D, established in 2010, is 600 international units, which may be taken in the form of a multivitamin, states Mayo Clinic. Recommended blood levels of vitamin D average 20 nanograms per milliliter and can be obtained through regular sunlight exposure.
Various amounts of vitamin D are recommended for patients to assist in treating, preventing or improving various medical conditions as well as to increase overall lifespan, notes Mayo Clinic. Individuals with heart disease, for instance, benefit from a daily dose of 10 to 25 micrograms of vitamin D2. Those wishing to enhance cognition may consume 528 to 9,000 international units of vitamin D2 or D3 for up to 40 weeks, while muscle weakness may be improved by consuming an average of 100,000 international units of vitamin D for up to a year.