The Mediterranean diet emphasizes nutrient-rich foods that are critical in building a strong immune system. (For Spectrum Health Beat)

If you want to do all you can to strengthen your immune system this winter, look first to diet and lifestyle.

The best defense against menacing viruses like cold and flu is to eat right, exercise and get plenty of sleep, said Kristi Veltkamp, RDN, a Spectrum Health registered dietitian.

In some cases, you could consider taking supplements—but you should talk to your doctor first.

“I think it’s not necessarily one thing that is going to be that magic pill,” Veltkamp said. “It really has a lot to do with your overall lifestyle.”

Certain vitamins help strengthen or maintain the immune system, Veltkamp said.

Vitamin D, for example, is a good immune system booster, although it’s difficult to get enough of it through food alone. It can also be difficult to get in the winter in Michigan, because the best source of vitamin D is the sun.

Exposing your arms, hands and face to sunlight for about 15 to 30 minutes at least three times a week is typically adequate for most people.

Zinc also helps the immune system. It’s usually available in protein foods such as meats, seafood, chicken and beans. It’s also in milk, cheese and some nuts.

Another important nutrient is vitamin C, which is relatively easy to get in foods. The recommended amount is 75-120 milligrams a day.

Bell peppers, citrus fruits, strawberries, broccoli and sweet potatoes are all good sources. Generally, you should get five servings of fruits and vegetables a day for enough vitamin C.

The right amount

A deficiency in any vitamin can be a problem.

Low levels of vitamin D may put someone at greater risk of catching a cold, while a zinc deficiency could increase the risk of more severe flu. A lack of vitamin C could increase the odds of getting cold or flu.

Your primary care doctor can help you determine if you have any vitamin deficiencies.

Ultimately, you should try to get what you need through a healthy diet before seeking any supplements. You get many nutrients from food, but usually only one vitamin through a supplement, Veltkamp said.

“Individuals don’t need supplements unless they have low amounts in their bodies,” Veltkamp said.

Keep in mind there are dangers to improper use of vitamins and supplements.

High doses of vitamin D can increase the risk of bone fractures and cause respiratory infections. Too much zinc can lead to low levels of copper, as well as decreasing the effectiveness of antibiotics.

“In these cases, more is not necessarily better,” Veltkamp said. “Adequate is good.”

Food first

If you’re looking for a meal plan that ensures you’re getting the proper amount of vitamins and nutrients, look no further than the Mediterranean diet.

The foods in this diet are rich in vitamins that boost the immune system, as well as containing nutrients that fight inflammation and increase antioxidants.

Turmeric and garlic, both components of the Mediterranean diet, can reduce the risk of a cold.

Quercetin—an antioxidant that fights viruses—is found in onions, tomatoes, olives and beans, all recommended items in the Mediterranean diet.

Omega-3 fatty acids, which help with brain and heart function, are found in fish and chia seeds, flaxseeds and walnuts, among other Mediterranean diet foods.

Along with eating right, you should avoid foods high in sugar and white flour, Veltkamp said. Sweet treats, pop and fried foods can depress the immune system, causing inflammation and more severe colds.

In addition to eating a healthy diet, you can strengthen your immune system by getting enough sleep, exercising regularly, maintaining a healthy weight and reducing stress.