5 min|Dr. Maya Kuczma

How Your Immune System Develops

Wellness, Education, Immune Health

Although we are born containing the structures that will make up our immune system, as well as thousands of genes that contribute to its ability to response, the immune system is fairly immature.

From infancy through childhood, our immune system undergoes massive changes to mature into a defense system that can recognize threats, mount a response, and restore us back to health when the threat is resolved. Here are 4 ways that the immune system develops:

1. A Healthy Start

In utero, our mothers can pass down some protection to infections they were exposed to historically, via antibodies, (1) but it is not until passage through the birth canal that we experience our first major exposure to bacteria, which will colonize various areas, including the skin, mouth, eyes, and gut, and begin to establish our microbiome. (2) The immune system undergoes significant development through infancy, largely influenced by this microbial exposure, and subsequent microbial exposure from our environment. The ‘old friends hypothesis’ argues that we have co-evolved with many of these microbes, and our immune system is now dependent on them to develop and function properly. (3)

Additionally, breastfeeding contributes to the development of our immune system by way of nutrients, antibodies, immune cells, and certain proteins contained in breast milk. (4) Maternal nutrient status and exposure to stress during pregnancy also appears to play a role in the development of an infant’s immune system; in particular, maternal stress during pregnancy has been shown to negatively impact the child’s immune system into adulthood. (5)

2. Play in the Dirt

After childbirth, microbial exposure continues to play a significant role in the development of the immune system. Current research suggests we may need exposure to many different microbes in order to identify and respond to threats; overtime, our immune system may build a database of what microbes can be considered friend or foe. (6)

Farm living (7) and exposure to dogs (8) during childhood appears to play a role in immune response, possibly due to extensive microbial exposure that aids in modulating the immune system. This supports the ‘hygiene hypothesis’, the concept that a child’s environment can be “too clean”, robbing their immune system from the sufficient exposure it needs for immune regulation.

Children naturally explore their environment with their hands, often touching various surfaces and trying to put things in their mouth, creating significant exposure to a wide variety of bugs. For a more, ‘directed' exposure, fermented foods, such as natto, kimchi, kefir, pickles, sauerkraut, yoghurt, and kombucha, are additional sources of microbes, and may signal and regulate the immune system. (9)

3. Not All Bugs Need Drugs

Research has shown that elimination of microbes by way of antibiotic treatment can alter the microbiome for years. (10) These changes may predispose children to health concerns later in life; early antibiotic use may play a role in the development of obesity; (11) metabolic diseases; (12) autoimmunity; (13) and asthma and atopic dermatitis. (14)

This is not to say antibiotics should not be used, but emphasizes the need to use them wisely. Although both bacteria and viruses cause infections, antibiotics only work to treat bacterial infections. (15) Using antibiotics only when needed can help limit the development of antibiotic-resistant bacteria, while also protecting a child’s internal ecosystem, and their developing immune system.

4. Stack the Building Blocks

As with adults, adequate nutrient status is an important contributor to immune system activity in early life. Zinc, vitamin C, vitamin A, vitamin D, and selenium, in addition to many other nutrients, are vital for healthy immune system development. Undernourished children typically exhibit defects in both their innate and adaptive immune systems. (16) Vitamin D status appears to play a significant role in the development of immune tolerance; vitamin D deficiency in childhood has been linked to improper immune responses, such as asthma.

(17) However, in a study comparing vitamin D supplementation with UV exposure, children had a greater decrease in inflammatory markers in response to UV light than with vitamin D supplementation alone. (18) Our immune system development likely depends on both UV exposure and intake of vitamin D (via food or supplementation).

From birth throughout childhood, the immune system is constantly adapting, learning from the environment and what we are exposed to, and responding accordingly. Our health today is in part a reflection of how we came into the world, and our early childhood experiences. It is evident that a healthy pregnancy, natural childbirth, breast-feeding, healthy childhood diet, and interactions with the outdoor environment can build the foundation for a healthy immune system.

But what about adults who didn’t get this strong start?

Many people were not breastfed or born vaginally, or did not get adequate nutrition during the early years. Additionally, many of us were prescribed antibiotics inappropriately, in cases of viral infections, many times throughout our childhood and adolescence.

Keep an eye on the blog where we will continue to dive into various factors that influence the activity of the immune system throughout our lifetime, and what you can do for your immune system today.