We really don’t have a ‘cold and flu season. We have a ‘low level of Vitamin D so poor immune function’ season.
Vitamin D could be called the mother hormone. It is essential, and very few foods in nature contain it. The flesh of fatty fish (such as salmon, tuna, and mackerel) and fish liver oils are among the best sources, and small amounts of vitamin D are found in beef liver, cheese, and egg yolks.
Our bodies will make it, if we expose enough skin to enough sunlight – without sunscreen – something many of us are unwilling or unable to do.
Since Vitamin D is fat soluble, anyone whose fat digestion is impaired [like someone whose gall bladder has been removed] will have trouble absorbing the oil form.
We stock Biotics Bio D-Mulsion Forte, an emulsified Vitamin D that has about 700 2000 IU drops per ounce, and costs $20.