Flu and colds are winter phenomena because in winter people don’t get sunshine and don’t get their maintenance dose of vitamin D thereby. You can get vitamin D-3 5000 iu gelcaps at WalMart. My wife is a schoolteacher and for thirty years has brought home whatever flu and colds were going around at school. We have both taken the D-3 10,000 iu(what you get in an hour or so of summer sun) a day since early September this year. Mrs. did not bring home any maladies including the H1N1 which laid all the kids out in October.
I do have some D with my Calcium. I will check out a larger dose!