As DC draws nearer and the flu is in full swing; something to consider is your health. The last thing that you want to happen is to be sick on the field trip. While you can't always prevent illness (I found this out the hard way the last few weeks) you can take steps to lessen your chances of exposure or improve your immune system.
Washing your hands and following proper hygienic practices will help stop germs from entering your body. To improve your immune system, try adding fresh fruit to your diet. Many fruits contain all the daily Vitamin C you need, and many other nutrients. Other minerals to look for are zinc and calcium. Zinc can be found in nuts and meat; particularly fish. Calcium is in dairy goods.
While multivitamins or products like Emergence-C are appealing, in that they often offer a lot of those vitamins and/or minerals, your body tends to have a hard time absorbing them from those sources and whole foods will always be a better option.
