Common nutritional advice tells us that taking large amounts of vitamin C will help keep the winter ills and chills away? Unfortunately there is not scientific backing to this, but what is known is that vitamin C is important in fighting infections. 

Vitamin C (known as ascorbic acid) works as an antioxidant to protect our bodies from free radical damage, and is also involved in the growth of our bones, tendons, ligaments and skin and increases the absorption of iron from our foods (particularly from vegetarian sources).

How much vitamin C we need depends on where we are in our life cycle, but the daily recommended dosages are, 
Age (years) RDI*
Infants and toddlers 1-3 35mg/day
Children 4-8 35mg/day
Adolescents 9-18 40mg/day
Adults 19-70+ 45mg/day
Pregnant women 60mg/day
Breastfeeding women 85mg/day
* Recommended Daily Dosage from NZ Nutritional Foundation 

However, as winter approaches some people believe that a higher dose is required to boost protection against the dreaded lurgies and support immunity all year round.