Throughout a human’s lifespan, the immune system is responsible for keeping out foreign substances and protecting the body. Though it is often thought of as a singular system, it consists of two separate sub-systems: innate immunity, and adaptive immunity. Critical early protection in babies is transferred directly from mothers, but when that fades, children rely on an immature immune system.
It develops stronger immune responses until it peaks in adulthood before diminishing as old age is reached. Because children have naive adaptive immune systems, they tend to rely more on their innate system (which is often fully functional by two years of age).
Ensuring the proper concentration of macro- and micronutrients is critical for a child’s health and prepares it for future encounters. The gut microbiota starts off as a nearly blank slate at birth, with its diversity then steadily increasing as we continue to be introduced to new microbes from the environment. Interacting with different microbes in the GI allows our body to learn how to distinguish friends from foes and support healthy relationships in the future.