Vitamin A can reduce the incidence and severity of infectious illnesses (Clin Infect Dis, 1994; 19: 489-99; J Nutr, 1995; 125: 1211-21). The usual dose is 8000-12,000 IU daily

B-complex vitamins such as B6, B12 and folic acid support immune function and are especially useful for stressed individuals (J Am Med Assoc, 1981; 245: 53-8; Clin Sci, 1984; 66: 241-8). Daily doses range from 25-100 mg as part of a complex

Vitamin C is the best-known immune-enhancing nutrient (see main story). Aim for 1000 mg daily

Vitamin E significantly decreases susceptibility to infections. Supplementation can benefit both the healthy and the ill (Arch Immunol Ther Exp, 1987; 35: 207-10; Ann NY Acad Sci, 1989; 570: 283-90). A daily dose should be around 200-400 IU

Ubiquinone (coenzyme Q10) can compensate for immune deficiencies due to ageing or disease (Med Hypoth, 1992; 38: 315-21; Mech Ageing Develop, 1978; 7: 189-97). Daily doses range from 20-200 mg

Zinc gluconate has shown a modest benefit on the duration of cold symptoms whereas zinc acetate did not (Clin Infect Dis, 2000; 31: 1202-8). Daily doses range from 15 mg for prevention to 100 mg during an infection

Selenium if deficient has been associated with lowered immunity. Its role as an antioxidant may be an important factor (Fed Proc, 1979; 38: 2139-42). Try 25-100 mg daily

Probiotics are technically not nutrients, but have a role in improving immune function (Immunopharmacol Immunotoxicol, 1992; 14: 331-40; Int J Immunother, 1993; 1X: 23-8). Supplements should contain at least three billion viable bacteria per capsule.