NUTRITION HOTLINE: Nutrition and Immunity

Q: I am recovering from disordered eating and seem to get sick all winter long. Is there anything I can eat or take to boost my immune system?

A: Nutrition and immune function are intricately linked. A study published in 2004 found that women who yo-yo dieted had decreased numbers of "natural killer cells" in their blood. These cells kill viruses and cancer cells, and having low natural killer cell activity has been linked to increased colds and infections, as well as a higher rate of cancer. In the study, women who had maintained the same weight for at least five years had 40 percent higher natural killer cell activity compared to women who had maintained their weight for less than two years. Restricting and dieting prevent your body"s immune system from operating at full capacity. So the fact that you are in recovery and maintaining a healthy weight will greatly benefit your immune system.

In addition, some other factors that influence immune response include protein intake, vitamins, minerals, probiotics, exercise, and sleep. Your body needs adequate protein in your diet from meats, poultry, seafood, dairy products, soy, legumes, and lentils to make immune cells. Check with your dietitian or doctor to see if you are getting enough protein in your diet. Vitamins and minerals involved in maintaining a healthy immune system include vitamin D, folic acid, vitamin C, vitamin E, vitamin A, vitamin B- 6 and B-12, zinc, iron, copper, and selenium. Foods that are good sources of these vitamins and minerals include dairy products, whole grains, meat, poultry, seafood, legumes and lentils, soy, fruits and vegetables, and nuts. Because these vitamins and minerals are found in a variety of foods and many of my clients have trouble with getting enough variety in their diets, I generally recommend a multivitamin and mineral supplement with 100% of the RDA, including iron.

I also recommend an extra supplement of 1000 IU vitamin D per day, and that your physician test your vitamin D level to see if you need more. Regarding extra vitamin C, current scientific data shows that it will not reduce the incidence of colds, but that up to 500 mg twice per day can reduce their severity and duration. So it doesn"t hurt to take extra if you have a cold! If you have had kidney stones, check with your doctor before taking extra vitamin C.

Probiotics are healthy bacteria that occur in dairy products, such as yogurt, kefir, cultured buttermilk, and cheese, and in garlic and sauerkraut. They work in your intestine to enhance immune function, so increasing your intake of these foods during the winter may help your resistance to certain bacteria and viruses. A study done in China found that children given probiotics had significantly fewer colds than control subjects. It is safest to consume probiotics through foods, and if you want to take them in supplement form, check with your physician or dietitian first.

Regular exercise will also enhance your body"s immune response. Studies have found that people who exercise regularly get sick less often than people who do not. Too much exercise however has the opposite effect, and you should not exercise when you are sick. Regular sleep is also essential for normal immune function. Studies have found that at least seven hours per night is key in fighting off illnesses, as your body makes immune cells while you sleep.