The idea that we can “boost” our immune health is appealing. However, there’s no evidence that a particular food, vitamin supplement or herbal preparation can improve the body’s immune system to the point that you have extra protection from infection.
What is fundamental to immune health, though, is a balanced, nutrient-packed diet. That’s because your immune system relies on a steady stream of nutrients to function optimally.
What is the immune system?
Your immune system is a complex and finely tuned network of cells and tissues throughout the body (e.g., skin, gut, spleen, liver, lymph nodes) that’s constantly working to defend against infection from harmful pathogens such as bacteria and viruses.
When the immune system recognizes a threat, it mounts a response by releasing white blood cells and other immune compounds that destroy foreign invaders.
Older adults tend to have a weaker immune system than younger adults. With age, it’s thought that the body produces fewer T cells – white blood cells that attack pathogens.
As well, insufficient levels of certain nutrients can be common in older people due to decreased appetite, chewing and swallowing problems, or reduced nutrient absorption in the gut.
A number of nutrients play a central role in maintaining a strong immune system – for its everyday functioning and for escalating its activity to fight infection.
Here’s how they work and which foods supply them. You may not have some of these foods on hand right now as we’re all told to practice social distancing, and that’s okay. Eat a variety of foods each day to consume a wide range of nutrients.
It reinforces our body’s barriers against invasion from pathogens by maintaining healthy epithelial tissue, which forms the skin and the lining of the respiratory, urinary and digestive tracts. Vitamin A is also needed to generate antibodies, which are immune cells that neutralize pathogens.
Preformed vitamin A is found in milk, yogurt, cheese, herring, salmon, tuna and liver. Beta-carotene is called provitamin A because it’s converted to vitamin A in the body.
Excellent sources of beta-carotene include sweet potato, carrots, butternut squash, spinach, kale, broccoli, red and yellow peppers, Swiss chard, mango, cantaloupe and dried apricots.
Because immune cells multiply quickly, this B vitamin is essential to form new immune cells and mount an immune response.
Outstanding sources of folate include cooked spinach, asparagus, broccoli, Brussels sprouts, green peas, avocado, lentils, black beans, kidney beans and wheat germ.
As an antioxidant, vitamin C protects immune cells from damage caused by free radicals, unstable oxygen compounds that are generated during the immune response. Vitamin C may also increase the production of immune cells that engulf and kill pathogens.
The best food sources include citrus fruit, kiwifruit, strawberries, mango, cantaloupe, red and green bell peppers, broccoli, cauliflower, Brussels sprouts, cabbage and tomato juice.
It’s thought that vitamin D has numerous effects on immune cells, which help to limit inflammation. It’s also involved in the synthesis of proteins that fight bacteria.
A vitamin-D deficiency has been linked to a higher risk of upper-respiratory-tract infections.
Very few foods contain vitamin D naturally; salmon and tuna are among the best sources. Fluid milk, many non-dairy milks and some brands of orange juice are fortified with the vitamin.
The current vitamin-D recommendation is based on how much we need to protect bones. It’s advised that adults get 800 to 2,000 IU (international units) of vitamin D from a supplement year-round to maintain a sufficient level of the nutrient in the bloodstream.
Like vitamin C, this antioxidant nutrient protects immune cell membranes from free radical damage and enhances immune function.
Good sources of vitamin E include wheat germ oil, sunflower seeds, sunflower oil, safflower oil, almonds, hazelnuts, peanuts and peanut butter.
It’s a vital component of the body’s two key antioxidant enzymes that protect immune cells from free radical damage. It also helps regulate immune cell function and inflammation.
Exceptional sources of selenium include Brazil nuts (1 nut provides almost two days’ worth), tuna, halibut, sardines, shrimp, beef, turkey, cottage cheese, brown rice and eggs.
Zinc is required for the growth and development of immune cells. The mineral is also used to synthesize antibodies.
You’ll find zinc in oysters, beef, crab, pork, chicken, pumpkin seeds, cashews, chickpeas, yogurt, milk and fortified breakfast cereals.
Leslie Beck is a dietitian.