The link between malnutrition and diarrheal disease is well-established, but understanding the precise mechanisms of the many connections remains a complex research frontier. Here’s one thing we do know: vitamin A is a key player in diarrhea prevention and treatment and in child health overall.

To understand why vitamin A has an impact on diarrheal disease, we need to start with an understanding of the roles vitamin A play in our bodies. For the purposes of diarrheal disease, vitamin A has three roles that are important:

• Cell differentiation (regulating the growth of new cells and assigning them roles)
• Epithelial lining/mucous membrane management
• Immune response

What is both a mucous membrane and an important infection prevention site in the body? The intestine.

While vitamin A deficiency can affect many types of tissue in the body, one trademark outcome is impaired replenishment of intestinal lining. Vitamin A deficiency interferes with normal cell growth, and we can see this effect most readily in the intestinal wall because it typically sees high cell turnover.

It’s not only the intestinal wall that suffers: immune cells require orderly cell differentiation, too. Without it, the standard sequenced immune response—including the orderly transition from innate to adaptive immunity—becomes disordered and less effective.

Many consequences of vitamin A deficiency converge in the intestine, which spells bad news for a child’s defenses against diarrhea infection.

As always, prevention is better than treatment, and the World Health Organization (WHO) recommends vitamin A supplementation where child mortality is high. Thankfully, vitamin A is also an effective treatment tool as well: by rapidly rallying the immune system, vitamin A reduces all-cause child mortality by about 1/3, and it specifically has an impact on diarrhea and measles mortality.

While we work to unravel other scientific mysteries surrounding gut damage, we have the data to act on what we know about the lifesaving impact of vitamin A (as well as zinc, breastfeeding, nutritious foods, and many other child health basics). We just need to do it.