Watch your vitamin A intake.

Many vitamin A supplements promise an immune boost, but people need to be careful about overdoing it. There are two forms of vitamin A: First, there’s beta–carotene and other carotenoids, which are found in plant foods like spinach and sweet potatoes. Carotenoids are converted into vitamin A only as your body needs it, so you really can’t eat too much. Then there’s preformed vitamin A, found in animal foods and some supplements (typically listed on vitamin labels as retinol or acetate or palmitate). Preformed vitamin A can build up and cause uncomfortable side effects such as nausea and dizziness. For this reason, you’ll want to avoid vitamin A supplements and get the bulk of your vitamin A from delicious vegetables and fruits like leafy green veggies, carrots, cantaloupe, and pumpkin. If you take a multivitamin, just make sure that at least 50 percent of the vitamin A comes in the form of beta carotene and/or mixed carotenoids.