"That traditional image of malnutrition that we're unfortunately so familiar with, of someone wasting away, that's just the external picture," said first author Claire Bourke, PhD. Bourke is talking about the hidden reality behind malnourished children. It is not always an unhealthy diet that causes this condition. A predisposition for malnourishment as predestined by a child’s genetic makeup plays a primary role in determining a child’s outcome. With the right mix of genes passed down from parents, a child could experience malnourishment even while consuming a healthy diet.
How is this possible? Scientists are quickly realizing, with new tools to study immunodeficiency, that immune defects cause malnutrition just as much as malnutrition causes immune defects. Immune dysfunction appears causative in the form of malabsorption, increased metabolic demand, dysregulation of the growth hormone, and greater susceptibility to infection - factors which exacerbate a malnourished condition.
“It doesn't just fight infection,” Bourke said of the human immune system. “It affects metabolism, neurological function, and growth, which are things that are also impaired in malnutrition."
On the other end of the spectrum, malnutrition can cause pro-inflammatory conditions from impairing function of dendritic cells, monocytes, and effector memory T cells. Together, immune dysfunction and malnourishment can create a state of impaired gut function and increased susceptibility to infection.
Scientists are now realizing the intricacies of the relationship between the immune system and nutrition by recognizing the connection between low numbers of white blood cells, weak skin and gut membranes, and malfunctioning lymph nodes.
Another part of the story is the epigenetic changes that occur in malnourished people that can persist through several generations. Children of malnourished parents have the potential of being affected very similarly by malnourishment, even if they make healthful eating choices. This effect is due to the inheritance of immune and metabolic genes, the expression of which has changed from a lifestyle of malnourishment.
Over half of all deaths in children five years old and younger are due to undernutrition. Even more, researchers find that the first thousand days of a baby’s life are extremely sensitive to diet and other environmental factors. With a new understanding how the malnutrition can be seen as an immune disorder, scientists are hopeful that reducing the prevalence of malnourished generations can help to reduce the burden of child mortality.
Sources: Cell Press, UNICEF, World Health Organization