There is lack of acquired immunity in populations across the world to COVID-19, no vaccine, uncertainty about the true infection rate within countries and, the elderly are a vulnerable group (particularly those in care homes and similar institutions). Nutritional advice is, therefore considered appropriate at this time. There is much evidence from animal and human studies that antioxidant nutrition and related nutrients support the immune system to function properly. The general advice is to eat a diverse and well-balanced diet rich in coloured fruit and vegetables (to increase the intake of antioxidant and associated nutrients) to support immune function. Specific advice in relation to the elderly is to increase the intake of Vitamin E (134 mg – 800 mg/day), Zinc (30 mg – 220 mg/day), Vitamin C (200 mg – 2 g/day) and particularly for those people with low serum vitamin D status, Vitamin D (10 μg – 100 μg/day). These nutrients have been shown to enhance T cell and B cell (antibody) immunity in human studies including in the elderly. There is no specific evidence these nutritional measures can help protect against, or even lessen the effects, of, COVID-19 infection. However, it does make pragmatic sense to support nutritionally both normal health and the immune system (with doses unlikely to be harmful) before, during and after COVID-19 infection. 

International Society for Immunonutrition (ISIN), Board members (March 2020). 

Laurence Harbige, Philip Calder, Ascensión Marcos, Mireille Dardenne, Gabriela Perdigón, Francisco Perez-Cano, Wilson Savino, Nora Slobodianik, Liseti Solano, Roxana Valdes.