By now, we all know what covid-19 is and that we can reduce our exposure by washing our hands frequently and by distancing ourselves from others where possible.
In addition to reducing your exposure, supporting your immune system is the next important step.
This will probably come as no surprise… the most important things that you can do to support your immune system so that it can effectively beat an infectious disease are the same things that support your overall health: get enough sleep, manage stress, and live an active lifestyle while avoiding overtraining. These are also the healthy lifestyle choices that are the easiest to let slide when life gets busy.
Sleep impact our health and our immune system is a major mechanism behind all of it! Just plain old “not getting enough sleep” causes inflammation. Even just three consecutive nights of inadequate sleep can cause measurable increases in markers of inflammation in the blood, straining our immune system so it’s less able to respond to a pathogen.
Our immune system cycles with our circadian rhythm, along with antibody formation (the way our bodies know to respond to super-specific invaders, like influenza or SARS-CoV-2), which predominantly takes place during sleep. So, someone who is not getting enough sleep is also not adequately forming antibodies. As a result, simply getting adequate sleep can protect you from infection. Studies examining differences or changes in sleep quality have found similar differences in immune function; basically, sleep quality and quantity is essential if we’re trying to protect ourselves from the flu season!
Some studies have specifically looked at how our regular sleep patterns impact our susceptibility to infection. A 2015 study in 164 healthy people, looked at how sleep impacted their risk of infection and clinical symptoms after being exposed to the common cold-causing rhinovirus (the researchers literally administered active rhinovirus up the participants noses!). After correcting for all other potential contributors, sleep duration was the biggest predictor of whether or not the people would get a cold (not sleep fragmentation or sleep efficiency). Sleeping less than 5 hours per night increased chances of developing a cold by 4.5X compared to 7 or more hours of sleep! Yikes! And getting 5 to 6 hours per night wasn’t much better; the risk was still 4.24X higher than people who got 7 or more hours sleep. And getting 6 to 7 hours of sleep per night still increased risk of getting the cold by 66% compared to 7 or more hours. Similarly, a 2012 prospective study in female nurses aged 37-57 with no pre-existing conditions showed those who routinely slept less than 5 hours per night had a 70% higher risk of getting pneumonia over the 4-year study period than those who routinely slept 8 hours per night.
The single best thing most of us can do to make sure we’re getting enough sleep (8 hours really is a good rule of thumb) is have a grown-up bedtime and stick to it.
#2 – Manage Stress
The best understood mechanism of the negative health impact of chronic stress is how it impacts immune function. Cortisol, the main stress hormone produced by our adrenal glands, alters the chemical messengers of inflammation (called cytokines) secreted by cells in the immune system. This changes how the immune system communicates with itself, turning on some aspects of the immune system, while turning off other aspects of the immune system. There are a wealth of studies to show that high cortisol causes inflammation. Chronic stress has been unequivocally shown to increase susceptibility to a variety of conditions, including autoimmune disease, cardiovascular disease, metabolic syndrome, osteoporosis, depression, cancer and infection.
In a 1991 study, participants’ stress levels were assessed based on a questionnaire before nasal administration of one of 5 different viruses that cause the common cold (1 strain coronavirus [not SARS-CoV-2], 3 strains of rhinovirus, and 1 strain of respiratory syncytial virus[RSV]). Rate of infection was 5.81X higher in highest stress participants compared to lowest stress (independent of which virus they were exposed to), and rate of developing clinical cold (meaning a symptomatic infection) was 2.16X higher. Another yikes! An 1966 prospective study of employees who worked at a military research instillation evaluated their stress levels six months before flu season and categorized them as either high stress or low stress. The high stress employees were about 3X more likely to get the flu the next season compared to the low stress employees. A more recent 2019 study looked at susceptibility to life-threatening infections in people with stress-related disorders (including post-traumatic stress disorder [PTSD], acute stress reaction, and adjustment disorder) compared to their full siblings without stress-related disorders and compared to matched controls from the general population. A stress-related disorder diagnosis increased risk of life-threatening infections by 47% compared to siblings and 58% compared to the general population. PTSD specifically, increased risk of life-threatening infection by 92% compared to siblings and 95% compared to the general population.
Mindfulness practice is a well-studied and effective strategy for managing stress (apps like Calm, Insight Timer and Headspace make mindfulness practice very accessible. Its also helpful to reduce your stressor load if possible, including reducing commitments if possible but also exposure to chemical stressors (like alcohol and tobacco), environmental stressors (like extreme temperatures) and sensory stressors (like crowded places). Other strategies to improve resilience to stress include: time in nature, exercise, laughing, cuddling with a pet, hugging and cuddling with a loved one, and making time for hobbies. There’s also a link between sleep and stress: getting enough sleep helps regulate the stress response and managing stress helps improve sleep quality. So, it’s always helpful to work on improving sleep and stress levels at the same time.
#3 – Get Moderate-Intensity Exercise
Exercise is one of those moderate stressors that can be really good for our bodies. All in all, it’s important to establish an exercise routine that incorporates a variety of movements that are both aerobic (generally, “cardio”-type exercises) and anaerobic (resistance training like weightlifting) in nature. There are many other reasons to have movement variability, including increased metabolic benefits and reduced risk of injury. Apart from this, studies have demonstrated that regular exercise promotes improved immune system function by reducing inappropriate cytokine activity, improving white blood cell function, and regulating cortisol release (both of which are also related to systematic inflammation – another reason why we need to tackle our health from all of these angles!). Plus, there is added benefit to light exercise when we’re already feeling a little sniffly: the activity may flush microbes out of the lungs and increase body temperature to help fight the infection!
A 2006 study of overweight and obese sedentary postmenopausal women, researchers compared 45 minutes of moderate-intensity exercise 5 days per week to 45 minutes of stretching only (also 5 days per week) over the course of a year. In the final three months of the study, the stretching only group had a 3X higher likelihood of getting a cold compared to the exercise group. But, you don’t have to work out for 9 straight months before your immune system benefits. In a 2005 study of healthy women aged 45-65 year, the researchers looked at how exercising for 30 minutes at a moderate intensity (60% max heart rate) 5 times per week affected rates of upper respiratory infections over 12 weeks. Exercising resulted in a 25% fewer episodes of upper respiratory infections compared to the control group. Even getting out for a walk is beneficial. In a 1993 study evaluating risk of common cold in older subjects over a 12-week period, the researchers found that the incidence of of the common cold was 8% in elderly women who already exercised at moderate intensity regularly, 21% in previously sedentary elderly women who walked for 40 minutes 5 times a week during the study, and 50% in the sedentary control subjects.
Avoiding high-intensity and strenuous workouts is important though (see Why Exercising Too Much Hurts Your Gut). It’s well established that athletes have a higher risk of upper respiratory infections, especially during periods of heavy training and competition. Studies have shown that this may be due to an increased window of susceptibility to infection in the hours following strenuous exercise, due to a temporary suppression of immune function.
Walking is a great place to start if you’re not very active right now, aiming for at least 150 minutes per week (that’s a 30-minute walk 5 times per week). If you’re already a gym buff, adding in a daily walk can still be very beneficial for immune health and stress management (and it’s important to re-evaluate whether or not those tough workouts are the best idea right now).
So what about supplements?
Some important micronutrients can specifically make us more resilient by supporting healthy immune function.
Vitamin A is a vital component of both the innate and adaptive immune response. This vitamin maintains the structural integrity of mucosal cells (think the lining of your respiratory tract and gastrointestinal tract!), so it is essential for keeping our first line of defense physically intact. Plus, it is needed for proper function of a host of immune cells (i.e., natural killer cells, macrophages, neutrophils, lymphocytes, and more!). In fact, vitamin A was identified as an immune modulating nutrient as early as 1928! Vitamin A insufficiency is well-known to increase infection rate and mortality, especially in school-age children. And, vitamin A supplementation has been shown to improve antibody production in response to various vaccines. Also, many types of infection have been shown to deplete serum vitamin A, so our nutritional need for vitamin A may be higher during an infection (more data is needed to quantify this).
Foods rich in vitamin A include liver, other organ meats, fish, shellfish, butter, cheese, eggs sweet potato, butternut, carrots, spinach, kale and broccoli.
Vitamin C might be the most well-known immune support vitamin of them all. The main function that vitamin C holds is to act as an antioxidant within certain immune cells; this process actually creates reactive oxygen species to kill pathogens. Since we cannot synthesize our own vitamin C, it is crucial that we get enough of it in our food or through supplementation. However, a large meta-analysis have revealed that up to 2 grams daily vitamin C supplementation doesn’t reduce the incidence of the common cold, the exception being people under high physical stress including marathon runners, skiers and soldiers who do see about a 50% decrease in cold incidence. For the general population though, vitamin C supplementation shortens cold duration by an average of 8% in adults and 14% in children, and decreases the severity of the cold by about 5%.
The foods richest in vitamin C are citrus fruits, bell peppers, acerola cherries, guavas, blackcurrants, thyme, parsley, kale, kiwis, broccoli, brussels sprouts, lemons, papayas, strawberries and rose hips.
Vitamin D is another well-known immune modulator that is worth paying attention to. Normal levels of vitamin D promote genetic expression of several immune cells, including monocytes, macrophages, dendritic cells, and lymphocytes (this means that without vitamin D present, the amount of these cells that are generated is much less! That leads to a sub-optimal immune system, to say the least). There is now considerable evidence that suboptimal vitamin D status is associated with compromised immunity and increased infection risk. A meta-analysis showed that daily vitamin D supplementation (400IU to 4000IU daily, average 1600IU) decreased risk of upper respiratory infection by 49%.
Vitamin D is the only nutrient your body produces when exposed to sunlight. Foods rich in vitamin D include salmon, sardines, cod liver oil, canned tuna, egg yolks and mushrooms.
Vitamin E is a fat-soluble vitamin (meaning that we can store it in our fat and that it is absorbed with dietary fat) that is also responsible for maintaining proper immune function. Specifically, alpha-tocopherol (one of the forms of vitamin E) is known to prevent oxidation or damage to cell membranes and polyunsaturated fatty acids, which protects against systemic inflammation. A clinical trial of independently-living elderly people showed that supplementation with 200IU of vitamin E daily decreased the rate of infections by about 30%, including a 22% reduction in incidence of the common cold.
Foods rich in vitamin E include avocados, olives, mango, kiwis, peppers, salmon, trout nuts and seeds.
Zinc, one of the dietary minerals, is also important in maintaining immune system function, because it is needed for both development and function of immune cells. Like vitamin C, zinc is not stored in the body, so regular consumption of foods that contain zinc is essential for an optimal immune system. Similar to vitamin A, zinc deficiency is associated with increased infection rate and zinc supplementation is known to improve antibody titers after vaccination. In a 2006 clinical trial, children were given zinc (as zinc sulfate, 15mg daily increased to 30mg at the onset of a cold) and followed for 7 months. The number of colds in the zinc group was 30% lower than in the control group, and zinc supplementation shortened the duration of the cold and the severity of symptoms. And, the proportion of children with no colds during the study period was 33% in the zinc group versus 14% in the control group. In a 2007 study of elderly nursing home residents, having normal serum zinc levels reduced the rate of pneumonia by 50% compared to low zinc levels (normal zinc was 70 microg/dL or higher).
The foods highest in zinc are meat, shellfish, legumes, seeds, nuts, dairy, eggs, whole grains, dark chocolate, oysters and liver.
Other immune health nutrients include selenium, copper, manganese, iron and B vitamins (especially B6, B9 and B12). While deficiency is any of these can increase susceptibility to infection, supplementation has either yielded mixed and context-dependent results (worsening outcomes for some and improving outcomes for others) or null effects in clinical trials. So, it’s important to get sufficient levels of these micronutrients from whole food sources, and in general, supplementation is not advised. There’s also preliminary evidence that high intake of polyphenols can help reduce infection risk, although more data is needed (see Polyphenols: Magic Bullet or Health Hype?, Elevating Mushrooms to Food Group Status and Coffee as a Mediator of Health & Longevity).
According to Dr Sarah Ballentyne Phd, nutrient supplementation (except possibly vitamin D) has a far smaller impact on infection susceptibility than the lifestyle factors discussed above. When it comes to nutritional strategies to support immune function, the most important action item is to avoid nutrient deficiencies.
According to Dr Sarah Ballantyne, the above lifestyle factors and nutrient focus are by far the most important priorities, there are some supplements with antiviral properties that may offer additional protection. Please note that none of these have been tested against SARS-CoV-2!
Probiotics – Whether you get your probiotics form fermented foods or take a supplement, there’s evidence to support reduced rates of upper respiratory infections. For example, Koreans who consume 108-180 grams daily of kimchi had a 19% decreased risk of rhinitis (runny nose, usually caused by the common cold) compared to those who consumed less than 24 grams daily. And a 2011 meta-analysis of prophylactic probiotic supplementation showed a 42% reduction in people suffering at least one upper respiratory infection (and a 47% reduction for 3+ upper respiratory infections).
Elderberry – Scientific studies confirm that elderberry (Sambucus nigra) has antiviral, antibacterial and anti-inflammatory properties. Plus, elderberry can enhance the immune-modulating effects of probiotic bacteria like Lactobacillus acidophilus. A 2004 study showed that elderberry syrup (1 tablespoon 4 times daily for 5 days, taken at first sign of infection) could shorten the duration of influenza symptoms by 4 days. A 2016 study showed that elderberry extract could shorten the duration of the common cold and reduce severity of symptoms. And a 2019 meta-analysis showed that elderberry extract is effective at reducing upper respiratory infection symptoms, with additional studies showing that the mechanism may be direct viral inhibition.