Maybe someone should tell the uninformed journalist who wrote that recent headline to not suggest that to animals that make their own vitamin C naturally and don't ever get colds and flu.
Humans lost the ability to synthesize vitamin C generations ago when a gene mutation ceased production of a liver enzyme needed to convert circulating blood sugar into ascorbate.
Science suggests that hunter gatherers consumed over 600 mgs of vitamin C per day. The adverage intake from our modern diet alone is around 100 mgs per day. This low intake explains why scurvy continues to be a frequently misdiagnosed disease, particularly in this country.
Vitamin C is rapidly depleted in the human body from a whole host of events including sun exposure, tobacco smoke (including second hand smoke), most meds, allergies, stress, infections, silent inflammation, pregnancy - and certainly the common viral cold.