Winter is nearly here, and it’s getting cold out there. We’re staying inside, cloistered together, sharing bodily fluids, and trading germs. The sun is weak, if it’s out at all, our vitamin D levels are shot, and our immune system is suffering. Many of us are traveling in planes, trains, and automobiles tightly packed with other people in the same immune predicament. It’s the perfect breeding ground for the dozens of viruses responsible for upper respiratory tract infections like the common cold and flu.

What can we do?