Being Proactive Against COVID-19: Blood Biomarkers to Watch

By Julia Reedy, MNSP, December 13, 2021


A major threat of COVID-19 is its differential impact on people with pre-existing health conditions; from what we know so far, COVID-19 is more dangerous for people with cardiovascular disease, diabetes, chronic respiratory disease, hypertension, and cancer.[1] But if you (or someone you love) fall into this demographic, there are actions you can take to optimize your overall health and well-being—and your immune response to a potential infection. Here's a list of science-based changes to optimize blood biomarkers closely related to both immunity and chronic disease. And remember: everyone has the agency to bolster their immune system—and peace of mind—during a time when so much feels out of our control. 

As always, consult a medical doctor before taking any nutritional supplements that we recommend. If you have or suspect a medical condition, or are taking any medications, please consult a doctor before acting on any of our recommendations.


Vitamin D improves white blood cell numbers and lung infection risk

Common health conditions associated with low vitamin D: Cardiovascular disease, asthma, certain cancers

Vitamin D isn’t just your average vitamin—it also acts as a hormone in your body to help absorb calcium, which helps to maintain bone strength and health. But vitamin D participates in so many processes around the body relating to things like weight maintenance, mental health, the nervous system, heart health, and inflammation. 

How vitamin D relates to immunity 

Vitamin D has a direct effect on the immune system—it modulates concentrations of many different types of white blood cells, thereby directly influencing your ability to fight off an infection.[2] And while we can’t yet be sure about vitamin D’s relationship with COVID-19 risk, research does show that vitamin D deficiency is associated with a higher risk of acute respiratory infection.[3] Blood vitamin D concentrations also appear to play a role in a restful night’s sleep, which, as you’ll read in a later section, plays a critical role in keeping you healthy.[4]

What you can do to optimize vitamin D

  • Take a supplement: Vitamin D supplementation is one of the most common InsideTracker recommendations because it’s notoriously hard to obtain through diet alone. And it looks like this recommendation is especially pertinent in today’s context: a meta-analysis (a study of multiple studies) found that vitamin D supplementation had protective effects against respiratory infections.[5] This was especially true for people who had low baseline levels of vitamin D (below 25nmol), which can be found in certain chronic diseases.
  • Get adequate sunshine: Vitamin D can be synthesized in the skin with a little sunlight. At least 20 minutes of daily, direct sunshine can help maintain optimal vitamin D levels.[6]
  • Eat vitamin D-rich foods: Though it is indeed hard to get enough vitamin D through diet alone (particularly if you don’t eat animal products), we always recommend building your diet to include key nutrients. Fish like halibut, snapper, and sockeye salmon are all great sources. Vegetarian sources include mushrooms and non-dairy milks (because they’re usually fortified).

Vitamin D immunity

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In stressful times, cortisol can reign supreme—and impair your immune system

Common health conditions associated with high cortisol: Cardiovascular disease, diabetes, hypertension

Commonly called “the stress hormone,” cortisol is classically known for being triggered in response to stressful situations, ranging from emotional to physiological ones. And this response is really important in our everyday lives: it helps us do things like wake up in the morning and work under pressure. But cortisol isn’t meant to be maintained at high levels over time—and when it is, it can have detrimental effects on the body.

How cortisol relates to immunity 

The relationship between cortisol and the immune system is complex—in normal concentrations, cortisol is essential for the development and maintenance of immunity.[7] But when cortisol levels spike or remain elevated over time, our immune system can suffer. In fact, one study found that people who experienced a stressful event—and a subsequent cortisol spike—were more likely to have high measures of inflammation, low levels of lymphocytes (a key type of white blood cells), and ultimately get a respiratory infection than those who didn’t.[8] It's for this reason that all of us—particularly those with pre-existing conditions—should focus on keeping our cortisol levels in check. 

What you can do to optimize cortisol

  • Practice mindfulness: Perhaps the most powerful tool we have against elevated cortisol levels is a robust practice of mindfulness and meditation. Numerous studies have found that regular meditation can significantly decrease cortisol levels, even in the long-term.[9] Subscribing to a guided meditation app can be a great way to get your practice started.
  • Get adequate exercise—but don't overdo it: Gyms around the world are closing, but think on the bright side—scaling back on training can actually support your immune system. One study found that reducing the intensity of weight training (i.e. lighter load, more reps) resulted in lower cortisol levels, yet still matched the strength and power gains of higher intensity weight training .[10] 
  • Supplement with ashwagandha: Ashwagandha is an herb that dates back to ancient medicine. And modern medicine has picked up on its benefits—in one study, ashwagandha significantly reduced cortisol levels in subjects who were subjected to stress.[11] To read more about ashwgandha's incredible impact on stress, read this blog.
  • Focus on belly fat: One study found that cortisol levels are positively correlated with waist circumference. In other words, the more body fat distributed around the belly (instead of around the hips, for example), the more cortisol in the blood.[12] While losing weight is never a trivial feat, it’s important to be cognizant of potential weight gain, particularly at times in which you may be more sedentary than usual.  

foods for cortisol


Moderate levels of hsCRP protect your cells, but high levels can leave you vulnerable

Common health conditions associated with high CRP: Coronary heart disease, diabetes, hypertension

High sensitivity C-Reactive Protein (hsCRP) is a marker of general inflammation throughout the body. Many chronic diseases promote an inflammatory state in the body, which can lead to elevated CRP levels. Because it’s not a particularly specific marker of inflammation, CRP can respond to a wide range of things like exercise, alcohol intake, and injury.

How hsCRP relates to immunity 

Like other biomarkers of inflammation, CRP exists to protect your cells against things like infection by activating immunity pathways.[13] And because of this responsiveness, high hsCRP levels can be useful for flagging the presence of an infection. But if inflammation is high at baseline, it can also make the body vulnerable to said pathogens, as high levels of hsCRP are associated with an impaired immune response. Therefore, people with pre-existing conditions should prioritize lowering their hsCRP levels to give their bodies the best possible fighting chance against a potential infection.

What you can do to optimize CRP

  • Again, get enough exercise: Like markers of blood glucose, regular aerobic exercise can help to regulate levels of inflammatory markers like hsCRP.[14] It’s important to not overdo it, though, as that can push your immune system beyond the brink, particularly if you’re experiencing symptoms “below the neck” (e.g. chest congestion, heavy coughing, upset stomach) or have a fever. Thirty minutes of daily, moderate-intensity exercise (like a jog) should do the trick. Not sure whether your symptoms constitute a day off? Check out our blog on the topic.
  • And another reminder to get the right amount sleep: A study of over 56,000 women found that people who get less than 5 hours or more than 9 hours of sleep have a significantly higher risk of pneumonia than those who regularly sleep for 8 hours per night.[15] Chronic sleep restriction (loss of 4 hours of sleep per night) can also lead to increased levels of CRP.[16] So what’s the goal? 7-8 hours of sleep each night!
  • Incorporate probiotic foods: Probiotics contribute to a wide range of health benefits, and inflammation is no different—one meta-analysis found probiotics can significantly reduce CRP levels.[17] For more info on how probiotics can support your immune system against respiratory infections, check out this blog.

anti-inflammatory foods


Glucose and HbA1c: Of particular note for those with diabetes

Common health conditions associated with high glucose markers: Type 1 and 2 diabetes

Blood glucose is a short-term measure of the concentration of glucose (a basic sugar) in your blood. Healthy levels are associated with better weight control, increased energy, and improved mood and cognition. Hemoglobin A1c, or HbA1c, provides more insight into your overall health because, unlike blood glucose tests, which are only meant to reflect the short-term, your HbA1c value reflects your average blood glucose concentration over the previous three to four months. It’s for this reason that high HbA1c levels can lead to a diabetes diagnosis, which is characterized by chronic misregulation of blood glucose levels.

How blood glucose and HbA1c relate to immunity 

The connection between glucose biomarkers and immunity is particularly important to people with diabetes—hyperglycemia (very high levels of blood glucose) can directly impair multiple aspects of the immune system's response to infection.[18] Therefore, people with diabetes have an increased susceptibility to develop infections and also face a greater risk of complications. Those with any form of diabetes (pre-, type 1, type 1.5, type 2, or gestational diabetes) should be extra cognizant of blood sugar levels during this time while infection risk is higher than normal.

What you can do to optimize blood glucose and HbA1c

  • Eat more fiber: Fiber is a critical component of any healthy diet—it promotes healthy digestion by keeping us fuller longer, feeding the healthy bacteria in our gut, and slowing the release of nutrients into our bloodstream. You should aim for at least 25-38 grams of fiber per day—around 2 cups of black beans or 3 cups of raspberries. 
  • Get moderate-intensity exercise: Aerobic exercise (e.g. running, swimming, cycling), with or without resistance training (e.g. lifting weights) can help to regulate blood glucose in both the short and long term.[19,20] So don’t worry about gym access for now—utilize outdoor spaces to get your heart rate up.
  • Reduce your red meat intake: A large meta-analysis conducted in 2015 found that both processed and unprocessed meat intake was associated with higher fasting glucose levels.[21] This is likely due to the high saturated fat and heme iron levels in these products which both appear to interfere with insulin signaling. 
  • Get more sleep: Lack of adequate sleep is associated with impaired glucose control—it can also directly increase your risk of respiratory infection.[22,23] 
  • Consider a ginseng supplement: Ginseng supplements have been shown to both modestly lower blood glucose levels in people with and without diabetes and to support the immune system directly against respiratory infections.[24,25] You can read more about ginseng (and other) supplements’ effects on lung infections in this blog.

Soluble vs insoluble fiber

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A summary of bolstering immunity through blood biomarkers

The world feels scary right now, but getting familiar with your blood biomarkers—and what they mean for your health—is a great way to take back the power over your wellbeing:
  • Vitamin D helps to dispatch white blood cells around the body, so adequate levels are imperative.
  • Excessively high cortisol levels can weaken the immune system, so destressing techniques are key right now.
  • hsCRP can be a good sidekick to the immune system as a whole, but it can also get carried away. Keep inflammation levels low so that, if an infection takes hold, it can do its job.
  • Glucose and HbA1c are of particular interest for diabetics—now is the time to prioritize fiber-rich foods and moderate exercise. 

Reedy Headshot (3)Julia Reedy, MNSP
      • Julia is a Written Content Strategist & Editor at InsideTracker. She loves to use her experience in cutting-edge nutrition research and writing to spin complex health and nutrition topics into clear, approachable info everyone can relate to. As an inquisitive food shopper, she's constantly reading ingredient lists—and leaving shelves of backward products in her wake.






[4] Huang W, Shah S, Long Q, Crankshaw AK, Tangpricha V. “Improvement of pain, sleep, and quality of life in chronic pain patients with vitamin D supplementation.” Clin J Pain. 29.4(2013): 341-347.



















[23] Prather AA et al. (2015) Behaviorally Assessed Sleep and Susceptibility to the Common Cold. Sleep. 38(9): 1353-9.



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