Winter is flu season because the sun is at a low angle and people cover up their bodies and do not get sunshine on their skin. Taking vitamin D3 is a substitute for the Sunshine D that is missing in winter. I have not had flu or any cold since I started taking D3 supplements 15 years ago. Same goes for my daughters, son, wife, friends and cousins.
I’ve never had the flu and I’m 65.
But I live in Florida!...................
And vitamin K too, right?