We have this amazing powerhouse in our bodies that we know as our immune system, and as long as it has all the “fuel” it needs, it’s very effective at protecting us against pathogenic organisms that make us sick. The strength of our immune system has been in the spotlight more than ever with our current pandemic.
There are factors that affect our immune system that we have no control over, such as genetics and stage of life (e.g. pregnancy, infancy and old age) that may make our immune system more susceptible, but there are many modifiable factors that influence the immune response, such as stress, physical fitness, obesity and diet.
Let’s focus on the role nutrition plays on the immune system. Without getting all biochemical on you, let’s keep it simple.
Proper nutrition provides:
Fuel and nutrients for the immune system to function.
Building blocks for the production of antibodies and other components of the immune system.
Regulators of immune cell metabolism (ie: vitamin A, zinc).
Nutrients with specific antibacterial or anti-viral functions (ie: vitamin D, zinc).
Protection from oxidative and inflammatory stress (e.g. vitamin C, vitamin E, zinc, selenium, long-chain omega-3 fatty acids and many plant polyphenols).
Support for the gut microbiota, which plays a key role in our immune health.
Deficiencies of these essential micronutrients will impair our immune system and therefore, increase susceptibility to infections. Thankfully, it’s never too late! An impaired immune system can be strengthened by changing your diet and repleting the deficient nutrients.
What are micronutrients anyway, you ask? When you hear that term, it’s generally referring to vitamins and minerals. It should be no surprise to you that, even in first world countries where food is abundant, people can be undernourished. Think about it, we should be consuming at least 5 servings of fruits and vegetables per day, plus whole grains and healthy fats. How many people do you know who are meeting those requirements? Are you? Unfortunately, most people are lucky to get in one or two servings a day, and most grains are processed (ie: white rice, white flours), not whole, which can lead to a nutrient deficient diet.
There are certain nutrients that have been touted in the media lately due to their possible benefits to boost the immune system, particularly to help reduce the effects of COVID-19. In particular, it seems the benefits of Vitamin D and Zinc have been shouted from the rooftops.
Vitamin D seems to be some kind of miracle cure, where it seems like every week there’s a new study that comes out about how the vitamin helps yet another condition. More recent studies have linked low vitamin D status to increased severity and hospitalization with COVID-19.
The jury is still out in regards to how much vitamin D we should supplement to protect against the effects of COVID-19, and unfortunately, the same goes for how much we need in general. I personally think that we are continuously discovering benefits of vitamin D on more and more health systems, so the science just can’t keep up. What I can tell you is that the recommended daily allowance (RDA) is 600-800 IU for adults, but a whopping 6400 IU is the recommended intake for lactating women to ensure an adequate supply is getting into their breast milk for their babies. For vitamin D deficient individuals who are at risk of infection, it has been recommended that they take 10,000 IU to raise blood concentrations to normal levels and then continue with 5000 IU per day for maintenance. The tolerable upper intake level (UL) is 4000 IU per day, but as much as 10,000 IU a day has recently been considered safe by the Endocrine Society. Research has also shown that race and obesity plays a factor in the effectiveness of Vitamin D supplementation and immunity, specifically to COVID-19. In the end, you have to consider your personal situation and decide which intake is best for you (or ideally, consult a registered dietitian or your doctor to help you).
What foods are rich in vitamin D? Vitamin D is a fat-soluable vitamin, so you will find it in animal products, like fish, chicken and pork, as well as egg yolk. You will also find vitamin D in white mushrooms!
Zinc supports the activity of many cells of the immune system and has specific anti-viral actions including inhibiting the replication of coronaviruses (hence it’s popularity during the COVID-19 pandemic).
Intakes up to 40 mg/day of zinc in foods and dietary supplements for adults are safe. You have to be careful overloading zinc because higher intakes can cause side effects, like nausea, vomiting, loss of appetite, abdominal cramps and diarrhea. Chronic consumption of high intakes (150–450 mg/day) can have the counterproductive effect of reducing immune function. The RDA for zinc is 8 mg for women and 11 mg for men, but if you are feeling a cold coming on, you can consume up to 40 mg a day and still be safe.
Food sources of zinc are mostly animal sources, like red meat, shellfish, eggs, legumes, nuts and seeds.
To prevent this article from becoming a whole research paper, I just mentioned these two micronutrients here because they are “hot” right now, but of course, there are many more nutrients that are detrimental to our health and the health of our immune system. Vitamin A also plays a key role in our immune health, as well as Vitamin E, B6, folate, B12, C, selenium, iron, omega-3 fatty acids and more.
So, what should you be eating, then? The general rule of thumb is that old adage, “eat the rainbow” and I want to add “eat brown” too - your grains should be brown, not white. Also, add nuts, seeds, legumes, oily fish (ie: salmon) and lean meats. If most of the food you consume fits into these categories, you should have most of your bases covered.
If you have a condition that may cause a deficiency in a nutrient(s), you should consider supplementation. That’s where you need to contact your dietitian to discuss what’s best for you to keep your immune system healthy and strong.
Finally, let’s not forget the importance of non-nutritive factors on our immune system: alleviation of stress, adequate sleep and physical fitness. You can eat as healthy as you want, and it will definitely help, but if these factors are weighing you down, your immune system will still take a toll. Just getting outside and taking a walk can help with all three of these components.
You know what you need to do, it just needs to become a habit, so stop procrastinating and start now! Your immune health is counting on it!
Graphic is from the European Journal of Clinical Nutrition (2021) 75:1309–1318