When you think of immune system boosting nutrients, the first thing that springs to mind is probably vitamin C. Vitamin C is a versatile nutrient that plays an important role in a wide range of body systems and biological processes—from supporting your adrenals when you’re under stress, to supporting immune system health and shortening the duration of illness. Five varied servings of fruits and vegetables a day will provide you with enough amount of vitamin C. Food sources include guava, kiwifruits, oranges, grapefruit, strawberries, bell peppers, broccoli, and tomatoes. 

Vitamin D is necessary for strong bones and immune health. When your skin is exposed to sunlight, it produces vitamin D from cholesterol. Food sources of vitamin D are limited—salmon, tuna, trout, and mackerel are among the best sources. Fortified foods, such as breakfast cereals and plant-based milk beverages, beef liver, cheese, egg yolks, and mushrooms will also help you to meet your daily dose of vitamin D.

Generally speaking, the recommended daily amount of vitamin D is 10 to 20 micrograms (mcg); 400 to 800 international units (IU). For infants and children aged 1 to 8 years, vitamin D intake is recommended at 25 mcg to 38 mcg (1,000 to 1,500 IU) and 63 mcg to 75 mcg (2,500 to 3,000 IU) respectively. For children aged 9 years and above, adults, as well as pregnant and lactating women, they should not have more than 100 mcg (4,000 IU) of vitamins D a day.

Zinc is an essential mineral for the production of new immune system cells, which also works as an antioxidant, helps increases metabolism and even speeds the healing process of wounds. It's important to note that individuals with low zinc levels, especially older people, are at higher risk of developing pneumonia. Top food sources of zinc include oysters, crab, lobster, beef, pork, chicken, baked beans, cashews, pumpkin seeds, oatmeal, yoghurt, and cheese. 

Iron plays a part in many of the immune system processes, including transporting oxygen to all cells in the body and boosting your energy levels. A lack of iron in the blood will lead to Iron deficiency anaemia, which can weaken the immune system, increasing your vulnerability to infection. To get a sufficient amount of iron, consume a variety of foods including red meat, seafood, poultry, iron-fortified breakfast cereals, lentils and legumes, spinach, nuts and raisins. Iron from plant-based sources is better absorbed when eaten with foods that contain vitamin C, such as oranges, kiwifruit, and tomatoes. 

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