Does milk prevent or promote inflammation? Insights from in vitro assays

Abstract

Milk is widely consumed worldwide due to its high nutritional value, having possible protection against infections and anti-inflammatory activity. Conversely, milk's vast microbiota reduces its shelf life and can pose risks to human health. Milk processing can introduce changes to its components, leading to speculation about its inflammatory potential. Chronic inflammation is associated with the development of a variety of metabolic, autoimmune, and degenerative diseases, being essential to understand the role of food in its etiology. This study aimed to investigate processed milk samples for their potential to modulate inflammatory responses in an intestinal in vitro model, contributing to the current debate about the effects of processed milk's consumption. Raw, pasteurized, and ultra-high temperature (UHT) homogenized milk were subjected to an in vitro simulated digestion process and human colorectal adenocarcinoma cells (Caco-2) and Abelson murine leukemia macrophages (Raw 264.7) were cultivated in vitro and challenged with milk samples from before and after digestion process. Post-digestion, pasteurized milk decreased the production of IL-8 in 59%, indicating an anti-inflammatory activity. UHT homogenized milk increased the production of assessed cytokines up to 238%, showing a pro-inflammatory response. Raw milk presented a 321% increase in IL-6 production, indicating a pro-inflammatory effect, as observed in processed milk samples. These new findings suggest that consumption of raw milk can be potentially inflammatory due to its vast microbiota, in addition to the well-known risks of its consumption and, that processed milk can prevent or promote inflammation according to the type of processing to which it was submitted.