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What Does a Low White Blood Cell Count Mean? The Answer Isn't Simple

By Ashley Reaver, MS, RD, CSSD, June 29, 2020

white blood cells lymphocyteWhile blood cells are the driving force behind a healthy immune system. But a low white blood cell count doesn't necessarily mean there's anything to worry about. In fact, white blood cell measurements from blood tests are best considered in context of your historic data and whether recent tests deviate from your normal. Here's a comprehensive overview of white blood cells, the reasons they might be low, and how to support their production.

What are white blood cells (WBC)?

White blood cells, or leukocytes, are the body’s primary defense against infection. They are largely produced in the bone marrow, although the spleen plays a role in the production of some types of white blood cells, too. The production of these cells is stimulated in response to infection, upon which they circulate throughout the blood and lymph systems.

Your total white blood cell count is the sum of five different types of white blood cells, all with different roles in battling foreign invaders in the body: neutrophils, eosinophils, basophils, lymphocytes, and monocytes.

Neutrophils make up the largest share of your white blood cell count, contributing 60-70% of the total. It's for this reason that a low white blood cell count is most likely due to a low neutrophil count, also called neutropenia. Neutrophils are the immune system’s first responders—within minutes of an injury, trauma, or inflammation to tissue in the body, neutrophils are drawn to the scene. They essentially control traffic to and from an infection site by recruiting additional white blood cells specialized to the type of invader. Neutrophils function by engulfing the pathogen and breaking it down. And even though they are microscopic, you’ve seen probably seen neutrophils, as they are the basis of pus! The lifespan of a neutrophil is very short, ranging from 5 hours to a few days.

Because your white blood cells play a vital role in immune function, low levels can leave you more susceptible to infection, increase the duration of illness, and increase the severity of it. It’s important to note that white blood cell levels can fluctuate daily and even hourly, so it’s important not to jump to conclusions about your levels from a single blood test. 

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blood cell types

What’s a normal range for white blood cell count? 

The definition of “normal” depends on the lab that processed your blood results. Generally, though, a normal white blood cell count is 4,000-11,000 per microliter of blood. This is usually reported as 4.0-11.0 thousands/μL. And if you get neutrophil counts measured as well, this corresponds to a count of1500-7800 cells/μL. You may also see this value represented as a percent of your total white blood cell count. 

 

The many causes of low white blood cells

First, before trying to pinpoint the cause behind a low WBC measure, it is important to note that a single data point really can't provide a comprehensive answer. Ideally, you should be able to compare recent blood results with past ones to identify a pattern or a deviation from your “normal.” The good news is that WBC count is frequently tested as part of a complete blood count (CBC) panel, a routine test you might've had at your doctor's office or if you’ve ever been hospitalized. So track down past blood work and use it as a comparison point for your new results—using multiple data points can help you determine whether you fall into one of the below categories. 

 

If your normal is lower than the defined normal range

The normal zones outlined above are based on the population as a whole. While they are well defined, they do not necessarily cover 100% of the possible values for a healthy, normal WBC. In fact, there is percentage of the population that has a lower “resting state” level of white blood cells. This is likely due to genetic variations and do not necessarily predispose you for an increased risk of infection. 1,2 Individuals of African, Middle Eastern, and particular regions of European descent may have be genetically predisposed to lower “resting” levels. 

If you have a history WBC levels just below the 4.0 thousands/μL normal cutoff and you haven’t experienced a high incidence of illness throughout your life, you likely just have a lower “resting state.” It is still important to discuss your findings with your physician to rule out the need for any additional testing.   

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If your white blood cell levels were once normal, but have been consistently low as of late

If you do not have a history of low WBC but have experienced a pattern of low results over recent months, you may be experiencing an issue with the production of white blood cells.[3] Of course, it is important to have historical data of your WBC to determine the pattern is new—levels right below the 4.0 thousands/μL cutoff likely aren’t clinically significant, but consistent values less than 3.5 thousands/μL—and definitely below 3.0 thousands/μL—should be discussed with your health care provider to determine the cause and assess follow-up testing. Causes range from relatively benign to more serious. Here a few:

Vitamin and mineral deficiencies

Some vitamins and minerals like vitamin B12 and folate play a crucial role in WBC formation. Low levels of vitamin B6, copper, and zinc may also play a role in low WBC production. A blood test can identify whether these nutrients are low, as you should not take supplements of these nutrients if your levels are normal. Chronic malnutrition and alcoholism can also result in these deficiencies, and can therefore also be a cause of low WBC.

WBC nutrient

Viral infections

Viral infections that last for several months (or indefinitely) can cause white blood cell levels to be chronically low. These include hepatitis B & C, HIV, and tuberculosis, among others. But you likely won’t identify such an infection from a single blood test, so it is important not to jump to conclusions from a single WBC measurement.

Autoimmune diseases

Low white blood cell counts can results from some autoimmune conditions (like rheumatoid arthritis), as autoimmune diseases attack the immune system.

Bone marrow cancers

Cancers that impact the bone marrow can cause low WBC counts, as most most white blood cells are produced in the bone marrow. WBC counts would be extremely low in these situations, not just mildly below the normal range.

Treatment and medication

Some people develop low white blood cell counts due to medical treatments or medications, most prominently chemotherapy. 

Infection

Individuals with chronically low white blood cell counts should be particularly cautious about infections. Hand washing is a critical step in preventing pathogens on the hands from entering the body through eating or contact with the face. Wearing a facemask is also a good idea to prevent inhalation of pathogens. Cuts and wounds should also be avoided as much as possible, and when a cut or wound is present, great care should be taken to keep the wound clean. Depending on the severity of low WBC, special consideration should also be given to the source and preparation of foods. 

 

You usually have normal white blood cells but your last test result was low

A short-term low white blood cell count is usually due to acute neutropenia, a short period of time in which absolute number of neutrophils in the blood are low.[3] Acute neutropenia is usually due to high neutrophil use in the body or low neutrophil production, which are common when your body is fighting off an infection. It's a relatively common occurrence and is tolerated well in the body. 

When an immune response is mounted, neutrophils leave the circulation to defend the body at the location of the damage. Since white blood cells engulf invading pathogens to destroy them, they tend to have a very short lifespan—most neutrophils can only effectively remove a few pathogens before they themselves die. This high usage of neutrophils results in a low level of them in the blood. And since neutrophils are the most common type of white blood cell, lower neutrophil levels bring down your overall WBC count. 

So don't be too stressed about a one-time low WBC measurement. If you are not feeling ill by the time you get your blood test results (they usually take several days to be processed), it is likely that your WBC count and neutrophil levels have retuned to normal since your blood draw. A single low WBC result means that your immune system is working as it should, especially if you never felt sick. 

 

Can exercise reduce white blood cell count?

Yes, high frequency of intense exercise, particularly in endurance sports, can reduce your white blood cell count and make you more susceptible to illness. This is often exhibited as upper respiratory infection in runners and cyclists during cold months.[4,5] Adequate rest days between high intensity workouts may help to reduce the incidence of upper respiratory infections. 

 

Can low white blood cells cause fatigue? 

Low white bloods cells likely aren’t the cause of fatigue. If you have low WBC and are increasingly feeling fatigued, both are likely symptoms of an underlying issue. This could be a range of issues, from over-exercise or overtraining, low folate or B12 levels, autoimmune diseases, viral infections, and certainly cancers.

WBC functioning-2

Ways to improve your white blood cell count

If your “resting state” white blood cell count is low, it’s unlikely that lifestyle changes will have an impact on your levels. For other causes of unoptimized white blood cell levels, there are some things you can do to help to reduce the demand on your immune system and increase its ability to protect you from foreign pathogens:

Manage your stress

Mental, emotional, and physical stressors all contribute to your body’s ability to defend itself from infection. The term allostatic load refers to the wear and tear on the body and brain as a result of stress. It is regulated by adrenalin and cortisol, among other compounds. As your body works to adapt to and deal with the biological causes of stress, its ability to manage resources for the immune defense response may be compromised.[6]

Get adequate sleep

The impact of inadequate sleep on white blood cells is well documented. Sleeping 6-8 hours per night can help you maintain normal levels of white blood cells, especially neutrophils.[7]

Engage in regular physical activity

The impact of exercise on white blood cell count and immune function is a U-shaped curve. That is, too little exercise and too much exercise can both increase your risk of infection. Routine, moderate-intensity exercise (e.g. 30 minutes of moderate intensity activity 5 days per week) has been demonstrated to support optimal white blood cell levels.[8,9] If you engage in high intensity training regularly without a rest day between activities, reducing the frequency of high intensity exercise can also be helpful in restoring your normal WBC level. 

Eat a variety of fruits and vegetables

Fruits and vegetables contain vitamins, minerals, antioxidants, and phytochemicals. These compounds can help to support the normal functioning of white blood cells and the immune system overall. In particular, focus on the antioxidants vitamin A, C, E and selenium. Vitamin A can be found in red, orange, and yellow-hued fruits and vegetables, as well as dark leafy greens. It is best absorbed when eaten with some source of fat and a mixture of fresh and cooked sources. Vitamin C is found in citrus, berries, broccoli, bell peppers, kiwis, and Brussels sprouts. Limited cooking is best to preserve vitamin C content. Vitamin E is mostly found in nuts and seeds. Wheat germ, wheat germ oil, sunflower seeds, and sunflower seed butter at the best sources. Selenium is found in the highest concentration in Brazil nuts. Two Brazil nuts per day provide the daily recommended amount.[10,11]

Maintain a healthy body weight

Excess body weight is associated with elevated levels of white blood cells, as it can cause an increase in inflammation and result in a WBC imbalance.[12] 

Stop smoking

Smoking causes your white blood cell count to be elevated, as it causes your body to be in a constant state of inflammation and damage caused by tobacco.[13]

 

The best way to understand your white blood cell count

Utilizing a history of blood data is the best way to understand a low white blood cell count. A single low WBC measure is not enough information for diagnosis. Speak with your physician about the need for follow-up testing. For most people, a low white blood cell level does not indicate illness or disease, but rather that your immune system is functioning properly. To maintain a properly functioning immune system, take action on improving lifestyle factors related to your white blood cell count. To learn what actions you can take to impact your white blood cell count, upload your results and develop your action plan with InsideTracker. 

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References

[1] Crosslin DR, McDavid A, Weston N, et al. Genetic variants associated with the white blood cell count in 13,923 subjects in the eMERGE Network. Hum Genet. 2012;131(4):639‐652. doi:10.1007/s00439-011-1103-9

[2] Reich D, Nalls MA, Kao WH, et al. Reduced neutrophil count in people of African descent is due to a regulatory variant in the Duffy antigen receptor for chemokines gene. PLoS Genet. 2009;5(1):e1000360. doi:10.1371/journal.pgen.1000360
[3] Boxer, Laurence A. “How to approach neutropenia.” Hematology. American Society of Hematology. Education Program vol. 2012 (2012): 174-82. doi:10.1182/asheducation-2012.1.174
[4] R. Horn, P L et al. “Lower white blood cell counts in elite athletes training for highly aerobic sports.” European journal of applied physiology vol. 110,5 (2010): 925-32. doi:10.1007/s00421-010-1573-9
[5] S. König D, Grathwohl D, Weinstock C, Northoff H, Berg A. Upper respiratory tract infection in athletes: influence of lifestyle, type of sport, training effort, and immunostimulant intake. Exercise Immunology Review. 2000 ;6:102-120.
[6] McEwen, Bruce S. “Stressed or stressed out: what is the difference?.” Journal of psychiatry & neuroscience : JPN vol. 30,5 (2005): 315-8.
[7] Faraut B, Boudjeltia KZ, Vanhamme L, Kerkhofs M. Immune, inflammatory and cardiovascular consequences of sleep restriction and recovery. Sleep Med Rev. 2012;16(2):137‐149. doi:10.1016/j.smrv.2011.05.00
[8] Johannsen, Neil M et al. “Effect of different doses of aerobic exercise on total white blood cell (WBC) and WBC subfraction number in postmenopausal women: results from DREW.” PloS one vol. 7,2 (2012): e31319. doi:10.1371/journal.pone.0031319
[9] Willis EA, Shearer JJ, Matthews CE, Hofmann JN. Association of physical activity and sedentary time with blood cell counts: National Health and Nutrition Survey 2003-2006. PLoS One. 2018;13(9):e0204277. Published 2018 Sep 25. doi:10.1371/journal.pone.0204277
[10] Gravina, Leyre et al. “Influence of nutrient intake on antioxidant capacity, muscle damage and white blood cell count in female soccer players.” Journal of the International Society of Sports Nutrition vol. 9,1 32. 19 Jul. 2012, doi:10.1186/1550-2783-9-32
[11] Colacino, Justin A., et al. "Dietary antioxidant and anti-inflammatory intake modifies the effect of cadmium exposure on markers of systemic inflammation and oxidative stress." Environmental research 131 (2014): 6-12.
[12] Vuong J, Qiu Y, La M, Clarke G, Swinkels DW, Cembrowski G. Reference intervals of complete blood count constituents are highly correlated to waist circumference: should obese patients have their own "normal values?". Am J Hematol. 2014;89(7):671‐677. doi:10.1002/ajh.23713
[13] Higuchi T, Omata F, Tsuchihashi K, Higashioka K, Koyamada R, Okada S. Current cigarette smoking is a reversible cause of elevated white blood cell count: Cross-sectional and longitudinal studies. Prev Med Rep. 2016;4:417‐422. Published 2016 Aug 9. doi:10.1016/j.pmedr.2016.08.009