Angela Dowden
Registered Nutritionist, American Council on Science and Health
The concept of boosting your immune system is attractive, especially in the unsettling era of COVID-19. But is it doable or even desirable? I took a look at this issue and here’s what you should know.
In March 2020, as the realities of COVID-19 hit, there was a huge and unprecedented spike in people asking the internet how to “boost” their immune systems. The concept of boosting your immune system is attractive, but is it doable or even desirable?
In fact, “boost” is entirely the wrong word in the context of COVID-19, where the worst symptoms are caused by the immune system going into overdrive.
Instead, what we need is an immune system that is in balance. Specific foods or supplements don’t seem to have much impact in achieving this, but eating a healthy diet, combined with getting enough exercise, not smoking, staying well hydrated, and having quality sleep do have a beneficial effect.
The available evidence suggests a Mediterranean-style diet does a good job of supporting our immune system. A study published 2018 in the Frontiers of Physiology found that healthy people aged 65–79 who ate a Mediterranean diet and took 10 micrograms (400 I.U.) vitamin D daily for a year were able to help offset age-related declines in immunity.
Specifically, the study participants ate a lot of vegetables, fruit, whole grains, pulses, and dairy, including an ounce of cheese daily. They also ate fish and a handful of nuts twice a week, along with modest portions of meat and eggs. Olive oil was the dietary fat of choice and a glass or two of red wine was allowed per night.
At the nutrient level, vitamins A, C, D, B6, folate, and B12, along with copper, iron, selenium, and zinc have all been associated with helping immune function. A balanced diet supplies these in adequate quantities for most people, except for vegans who need to take a supplement of vitamin B12 and women who may lack iron and require an appropriate prescription of the mineral.
Vitamin D supplements may also be needed, especially during winter when it’s not possible to get the nutrient from sunlight. Getting your vitamin D levels checked is advisable. For optimal immune health you’re aiming for a serum 25(OH)D concentration (the biomarker of vitamin D exposure in the blood) of around 75 nmol/L, but less than 125nmol/L. Too much vitamin D can be harmful and 50 micrograms (2000 I.U.) a day is the most you should ever need.
Intriguingly, our gut is home to 70 percent of our body’s immune tissue and provides a major line of defense between the outside world and our insides. Though the ins and outs are far from fully understood, the collection of microbes in the gut seem to have key worker status, protecting us with “friendly” native bacterial species, exchanging cross-talk with gut cells to survey health risk, and generating by-products hostile to the bacteria and viruses that could do us harm.
The simplest way to support the gut microbiome is to eat more plant-based foods whose dietary fibers and polyphenols boost beneficial bacteria. That’s another tick in the box for the Mediterranean diet (or similarly plant-focused plans like DASH or a flexitarian diet) and a down vote for keto and low-carb-high-fat diets, which often don’t provide fiber in sufficient quantities.
Ironically the “detox” diet, or juice fast you might consider to cleanse and reboot, is also not a good idea for dodging illness, as it rarely contains enough calories and nutrients to support the immune system.
Indeed, a little bit of what we fancy could be a better health strategy. That’s because a positive emotional state, brought about by eating small amounts of the foods we really enjoy (hello cake!) can help our immune system too.
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