Early Microbial Exposure Prevents Leukemia
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Story at-a-glance
- Among children born with a genetic mutation that can cause acute lymphoblastic leukemia (ALL), lack of exposure to common infections in the first 12 months of life may increase their risk of later developing a virus or bacteria that triggers ALL
- This “delayed infection” theory thus posits that “priming” the immune system via exposure to a variety of germs, dirt and microbes in early life is essential for its optimal function later
- Missing out on this key process, which is becoming increasingly common in developed countries that value regular disinfection and antibacterial cleaning products, could set the stage for the development of ALL
By Dr. Mercola
Exposure to microbes, or lack thereof, has long been named as a factor in developing diseases ranging from allergies to asthma. Acute lymphoblastic leukemia (ALL), the most common type of childhood cancer, may also have a microbial link, according to Melvyn Greaves of the Institute of Cancer Research in London, U.K.
In a landmark study, Greaves suggests that, among children born with a genetic mutation that can cause ALL, lack of exposure to common infections in the first 12 months of life may increase their risk of later developing a virus or bacteria that triggers ALL.
This "delayed infection" theory thus posits that "priming" the immune system via exposure to a variety of germs, dirt and microbes in early life is essential for its optimal function later. Missing out on this key process, which is becoming increasingly common in developed countries that value regular disinfection and antibacterial cleaning products, could set the stage for the development of ALL.
Is Missing Out on Microbes in Childhood Setting Up the 'Perfect Storm' for ALL?
Greaves' delayed infection theory is based on an extensive analysis of research, culminating in what he calls "two discrete steps" that cause ALL. First, before birth a genetic mutation occurs that's actually quite common; prior research by Greaves and colleagues suggests 1 in 20 children may have it. However, only 1 percent of those with the mutation will go on to develop ALL, such that children aged 15 and under have a 1 in 2,000 cumulative risk of developing the disease.1
The trigger for the disease occurs later in childhood, when an infection prompts another genetic mutation that activates the disease process, leading to ALL. This second trigger, Greaves believes, occurs when the immune system hasn't been adequately primed via exposure to microbes in early life. "Childhood ALL can be viewed as a paradoxical consequence of progress in modern societies, where behavioral changes have restrained early microbial exposure.
This engenders an evolutionary mismatch between historical adaptations of the immune system and contemporary lifestyles. Childhood ALL may be a preventable cancer," he says.2 Among Greaves' supporting research is a 2006 study that suggested influenza may trigger leukemia in some children.3 The study followed trends from 1974 to 2000; peaks in ALL diagnoses occurred in 1976 and 1999, both years that had flu epidemics just a few months prior to the ALL peaks.
Further, in mice with the ALL gene mutation, those kept in a sterile environment did not develop the disease but, once moved to an environment rich with microbes, the cancer developed.4 Greaves is now exploring whether exposure to microbes can prevent leukemia in mice, with the hope that the findings can then be investigated in humans. For now, however, Greaves' study suggests exposure to microbes in early life may be the ticket to preventing ALL, which can be done through:
- Vaginal delivery (versus caesarean)
- Breastfeeding
- Going to day care as a baby
- Exposure to older siblings
Past research supports these suggestions, including a 2002 study that found children who spent more time in day care had a significantly reduced risk of ALL.5 Breastfeeding was also associated with a reduced risk of ALL whereas introduction of formula within 14 days of birth was positively associated with ALL, as was exclusive formula feeding to 6 months.6
The Microbial Link to Cancer Keeps Growing
Researchers are only beginning to tap the surface when it comes to unveiling the complex relationship microbes have with human health and disease. Whereas persistent infections, and their related inflammation, have been shown to promote cancer, other pathogens may ignite an antitumor immune response that can even lead to cancer regression.
Writing in the journal Clinical Cancer Research, researchers explained, "Infectious agents and their products can orchestrate a wide range of host immune responses, through which they may positively or negatively modulate cancer development and/or progression."7
Whereas certain viruses, for instance, are known to directly promote cancer, it's likely that other viruses and other microbes act indirectly by way of modulating the immune response, although how this occurs remains a mystery. It seems, however, that infections during early life can be especially impacting.
You've probably heard of the hygiene hypothesis, which is the notion that a child raised in an environment devoid of dirt and germs, and who is given antibiotics that kill off all of the bacteria in his gut, is not able to build up natural resistance to disease and becomes vulnerable to illnesses later in life.
Your immune system is composed of two main groups that work together to protect you. One part of your immune system deploys specialized white blood cells, called Th1 lymphocytes, that direct an assault on infected cells throughout your body. The other major part of your immune system attacks intruders even earlier.
It produces antibodies that try to block dangerous microbes from invading your body's cells in the first place. This latter strategy uses a different variety of white blood cells, called Th2 lymphocytes. The Th2 system also happens to drive allergic responses to foreign organisms.
At birth, an infant's immune system appears to rely primarily on the Th2 system, while waiting for the Th1 system to grow stronger. But the hygiene hypothesis suggests that the Th1 system can grow stronger only if it gets "exercise," either through fighting infections or through encounters with certain harmless microbes. Without such stimulation, the Th2 system flourishes and the immune system tends to react with allergic responses more easily.
The Cancer Hygiene Hypothesis
The hygiene hypothesis posits that children and adults not being exposed to viruses and other environmental factors like dirt, germs and parasites results in their not being able to build up resistance, which makes them more vulnerable to illnesses. The so-called cancer hygiene hypothesis suggests that cancer is one of these illnesses. Even mumps, once a common childhood illness, may play a role in later cancer prevention, according to a study published in BMC Cancer:8
"Infections occur as early as the first year of life and may impact the immune system and cancer risk. The increase in antigenic exposure, after birth through viral/bacterial infections, may be essential for newborns to switch from a Th2 biased to a balanced Th1/Th2 immunity as well as to develop immunological memory.
Also, childhood diseases may activate specific antitumoral responses. For instance, mumps may lead to immune recognition of TAA present on ovarian cancer cells, resulting in an effective immunosurveillance."
It seems that not only the type of infection you're exposed to but also the timing shape how your immune system functions as well as your susceptibility to diseases like cancer.
"Some experimental evidence may also support the cancer hygiene hypothesis, that is, the antitumorigenic role of several inflammatory components, the ability of some commensals and benign gastrointestinal parasites like helminths to downregulate inflammation, as well as the ability of pathogens and their products to stimulate anticancer immunity," according to researchers writing in Clinical Cancer Research,9 who continued:
"Both protective and detrimental effects of microorganisms have been observed, many of them linked to various immune components. Overall, their effect may depend on the fine orchestration between induction and suppression of cancer-promoting or antitumorigenic immunity as well as on the level of pathogen load and the timing between infection and cancer initiation.
In this regard, cancer may be associated with the increased hygiene/decreased exposure to specific microorganisms, similar to what is known for autoimmune diseases and allergies."
Gut Microbes Also Linked to Cancer
Aside from the way microbial exposures affect your immune system, microbes may also play a role in cancer via those that exist in (and on) your body. For instance, beneficial bacteria known as probiotics can help boost activity of immune cells that fight off cancer cells. Certain gut bacteria also have shown potential for treating colon cancer,10 as well as boosting immune system health and reducing inflammation.
Research by Johanna Lampe, Ph.D., at Fred Hutchinson Cancer Research Center suggests microbial metabolism may affect your cancer risk for better or worse in many different ways, by influencing:11,12
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DNA repair
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Carcinogen metabolism / detoxification
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Hormone regulation
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Inflammation
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Immune function
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Apoptosis (programmed cell death)
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Microbial proliferation
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Microbial differentiation
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In fact, fermented foods, prized for their role in supporting gut health, may be a key part of an anticancer diet. For example, butyrate, a short-chain fatty acid created when microbes ferment dietary fiber in your gut, has been shown to induce programmed cell death of colon cancer cells,13 and cultured milk products may reduce your risk of bladder cancer by about 29 percent.14
So eating fermented foods, including lassi, grass fed kefir, natto (fermented soy) and fermented vegetables, preferably homemade, is one of the best ways to nourish your gut health and reduce your cancer risk.
Getting your hands dirty in the garden can also help reacquaint your immune system with beneficial microorganisms on the plants and in the soil. Even washing your dishes by hand, instead of in the dishwasher, may actually leave more "dirt" on the plates and thereby decrease your risk of allergies by stimulating your immune system. It's possible this immune stimulation could play a role in cancer risk as well.
Embracing Microbes for Your Health
Although the mechanisms are still not well understood, the accumulation of research showing health benefits from early, and continued, exposure to microbes in your environment suggests it's a key health strategy to take to heart. If you're healthy, exposure to bacteria and viruses may serve to strengthen your immune system and provide long-lasting defense against disease.
If you don't get this healthy exposure to germs in your environment, it may end up making you sick. Health problems already associated with the hygiene hypothesis include:
- Allergies
- Asthma
- Eczema
- Autoimmune diseases
- Heart disease, with one study finding that early exposure to viral infections during childhood could reduce the risk of heart disease later in life by up to 90 percent15
Even depression has been connected to early exposure to pathogens, via an inflammatory connection,16 so there are many reasons to avoid an overly sterile environment in the early years of life, even aside from potential cancer prevention.
As mentioned, giving birth vaginally, breastfeeding and allowing your children to be exposed to other children (either siblings or at day care) are prime ways to increase their microbial exposure in the first few months of life. You can also avoid being overly "sterile," and thereby bolster your body's healthy immune function, by:
• Letting your child get dirty. Allow your kids to play outside and get dirty (and realize that if your kid eats boogers, it isn't the end of the world).
• Not using antibacterial soaps and other antibacterial household products, which wipe out the microorganisms that your body needs to be exposed to for developing and maintaining proper immune function. Simple soap and water are all you need when washing your hands. The antibacterial chemicals are quite toxic and have even been found to promote the growth of resistant bacteria.
• Avoiding unnecessary antibiotics. Remember that viral infections are impervious to antibiotics, as antibiotics only work on bacterial infections.
• Serving organic grass fed meat and dairy products that do not contain antibiotics.
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