Vitamin A (both preformed and provitamin A) typically 10,000 - 15,000 units daily with 2,500 units being preformed vitamin A and the remainder being provitamin A which is beta carotene. The best form of the provitamin A is a mixed blend of natural carotenoids known as Betatene.

Vitamin E (400 - 800 units daily) The natural form of vitamin E is up to three times more bioavailable. In addition, a mixed blend of vitamin E (known as tocopherol) provides more benefit to the immune system than the alpha form of vitamin E alone (which is typically found in most vitamin E products sold).

Other nutrients shown to support immune function include:

Selenium in the form of selenomethionine (200 mcg daily)
B vitamins (25 - 100 mg daily)
Vitamin C (500 - 1000 mg daily)
Zinc (15 - 30 mg daily) best form is L-OptiZinc
Odorless garlic extract (400-900 mg daily)

In the event of an acute viral infection, specific herbs of benefit include:

Echinecea
Goldenseal root
Elderberry extract, tradename Sambucol