The number of cases of confirmed coronavirus (Covid-19) globally is rising from day today. Precautions such as washing hands, exercising, and getting enough sleep is the key to lowering the risk of exposure.

However, in preparing the immune system to confront this pandemic, take vitamins and supplements alone is not enough. A healthy diet can help improve the immune system.

It is important to note that no specific research done on foods that help fight COVID-19. Yet many studies find that there are certain foods that can increase and strengthen the immune system.

Here are nine foods that can boost the immune system, as reported by CNBC International:

1. Red bell pepper

Red peppers have vitamin C the most wealthy among other fruits and vegetables. According to the U.S. Department of Agriculture, one cup of red bell pepper chopped contains about 211% of vitamin C or two times more than the citrus fruits (106%).

The study of the National Institutes of Health (NIH) in 2017 found that vitamin C contributes to immune defense by supporting the various functions of the cells, can reduce the risk of respiratory infections, and helps the growth and repair of tissues in the body.

"Intake of vitamin C daily is very important for good health because our body does not produce it naturally," said Dr. Seema Sarin, a doctor of internal medicine in EHE Health.

2. Broccoli

Broccoli is also rich in vitamin C and contains vitamin E and antioxidants which can help fight bacteria and viruses. Half a cup of broccoli contains 43% of the value of vitamin C daily, according to the NIH.

"Broccoli is packed with phytochemicals and antioxidants that support our immune system," said Sarin, "To get the maximum results from vegetables this powerhouse, eat raw or only cooked slightly."

3. Chickpeas

Beans contain a lot of protein, and essential nutrients made of amino acids that help regenerate and repair the tissues of the body. According to the Academy of Nutrition and Dietetics, the chickpeas are good at synthesizing and maintaining the enzymes to keep the system in order to function properly.

"Chickpeas are also packed with zinc, which helps the immune system to control and regulate the immune response," said Emily Wunder, nutritionist and founder of nutritious recipes Healthier Taste.

4. Strawberries

Further, Wunder said half a cup of strawberries can already meet 50% of the requirement of human vitamin C per day. Wunder recommends adding chopped strawberries into yogurt, oatmeal, or consumed with wheat bread and peanut butter. "Of course, they fit with a smoothie too," he said.

"Vitamin C is great for strengthening Your immune system," he said, adding strawberries can help protect the cells from damage caused by free radicals and pollution in the environment.

5. Garlic

In the study of Advances in Therapy 2001 showed that consuming garlic two to three cloves per day can help ward off and recover colds.

"Garlic is not only full of flavor, but also contain health benefits such as lowering blood pressure and reducing the risk of heart disease," said Sarin, "the Ability to enhance immunity of Garlic comes from the high concentration of compounds containing sulfur, which can help fight some infections."

6. Mushrooms

A review 2018 about mushrooms as a source of vitamin D find that the "sunshine vitamin" can help improve the absorption of calcium, which is good for bone health and can also protect some cancer and respiratory diseases.

"Although sun exposure is the best vitamin D source, it can also be provided by some foods, including mushrooms," said Wunder, recommend to bake the mushrooms with 350 degrees Fahrenheit, use one to two tablespoons of oil, chopped garlic and a little salt and pepper.

7. Spinach

"Spinach is rich in vitamin C and full of antioxidants that help protect the immune cells of our body from environmental damage," said Sarin, "Plus, it has beta carotene, the main food source of vitamin A, an important component of immune function."

Like broccoli, the best way to consume spinach is by eating it raw or slightly cooked. To incorporate more spinach into the food, Sarin advised to mix it in a smoothie, or as a side dish sauteed with garlic.

8. Yogurt

"Yogurt is a source of probiotics which are good, which is the good bacteria that help promote intestinal and immune system healthy," said Sarin. Recent study also found probiotics to be effective to fight against common cold and respiratory infections such as influenza.

Sarin recommended to choose plain yogurt, than have a taste and add it with fruit and honey. "Or, You can add it to Your favorite smoothie," he said, adding those who do a milk-free diet can still benefit from a selection of yogurt almond milk and coconut milk.

9. Sunflower seeds

"Sunflower seeds high in vitamin E, which acts as an antioxidant and helps boost the immune system," said Wunder. According to the NIH, with just one ounce of roasted sunflower seeds can give You 49% of the value of vitamin E daily.

Sunflower seeds can be baked at a temperature of 300 degrees Fahrenheit until lightly browned. Then add the seeds to salads or toss with roasted vegetables. These seeds can also be a substitute pine nuts for the pesto sauce.