Why a Simple Stomach Bug Can Ruin Your Ability to Digest Dairy.

Pouring fresh milk into a glass.

Have you ever recovered from a nasty stomach bug, only to find that your next bowl of ice cream suddenly betrays your stomach? What if the sudden inability to digest ice cream wasn't a lifelong sentence, but just the lingering aftermath of a viral infection? Let's talk about the surprising link between rotavirus and lactose intolerance.

Lactose Intolerance 

Lactose intolerance affects around 68% of the world's population, and it’s due to something called lactose malabsorption. Lactose is a natural sugar found in the milk of mammals, but after a certain age, the human body technically does not require any ingestion of lactose. Because lactose is unable to enter through the lining of the small intestine due to its complexity and size, it must be broken down into glucose and galactose by an enzyme called lactase. Without lactase, these large sugar molecules cause symptoms like bloating, gas, and sometimes even diarrhea (Mayo Clinic, 2022). After early childhood, it’s not uncommon for the body to stop producing the enzyme lactase when the LCT gene is "turned off" in an event called lactase nonpersistence (MedlinePlus, 2020).

Viruses

Viruses are dangerous, and at times life-threatening, as we’ve seen from the most recent pandemic. We learned how viruses may cause significant physiological damage, some even being life-long alterations that are chronic conditions. We can observe patterns with different viruses causing different symptoms, like norovirus being one of the main causes of food poisoning that affects the gastrointestinal tract (GI tract), causing vomiting and diarrhea. Let’s take a look at a different virus, rotavirus, which may cause lactose intolerance in some. 

A detailed 3D rendering of a virus showing its distinct spike proteins on a spherical surface.

Rotavirus

Under an electron microscope, rotavirus has a distinctive, wheel-like shape and are double-stranded RNA viruses. Rotaviruses are able to survive in the air and even remain on surfaces for several hours (Dodet et. al., 1997). The method of transmission is via the fecal-oral route, meaning the virus is spread when someone accidentally ingests the pathogen from contaminated stool. There are 18 million cases worldwide, with almost 900,000 deaths annually. These deaths are most common in developing countries, but accounts for 25% of diarrhea-related deaths worldwide. Children are most at risk of getting rotavirus (CDC, 2024). 

The lactase enzyme is located on the brush border of the small intestine. Diarrhea results from rotavirus damage to the small intestinal epithelium function. This causes malabsorption, which is a digestive disorder that causes undigested complex sugars to transport into the colon, leading to diarrhea. As a result of infection, the expression of digestive enzymes of these infected enterocytes (specialized intestinal cells) are reduced, one of which being lactase (Ramig, 2004). Diarrhea in children is significantly caused by lactose intolerance, and recent studies show a potential link to rotavirus infections, as gut microbiota is altered (Shen, et. al., 2025). Researchers have found characteristic changes to the gut microbiota of children infected with rotavirus, compared to children who remained lactose tolerant (Ye et al., 2025). A clinical study found that out of ninety infants and young children with acute rotavirus gastroenteritis, 45 of them were "found to have an abnormal lactose breath hydrogen test (LBHT)," indicating lactose malabsorption, and two of them were clinically lactose intolerant (Lin, 1990). 

Luckily, a majority of infants in the US receive the rotavirus vaccine, which reduces the number of infections. Before the introduction of the rotavirus vaccine in 2006, rotavirus was the leading cause of acute gastroenteritis among children in the United States (Alpha, 2024). Hospitalizations among children in the United States have decreased by 80% (Boston Children’s Hospital, 2025). Vaccination remains highly effective in preventing hospitalizations associated with rotavirus.

Conclusion

There is a link between rotavirus infection to lactose intolerance due to damage to intestinal cells that produce lactase in the intestines that is responsible for lactase enzyme formation. This has been demonstrated in studies of children with rotavirus gastroenteritis, which found a significant association between the infection and the subsequent development of lactose intolerance as a secondary effect. Rotavirus vaccinations are widely available in the US, effectively reducing the risk of severe infection. As lactose intolerance is a secondary consequence of the virus, normal lactase function may return following intestinal recovery.

Written by and edited by Alyssa Cho, BS, and edited by Aldrin V. Gomes, PhD

References

1. Alpha Oumar Diallo, et al. “Rotavirus Vaccine Effectiveness against Severe Acute Gastroenteritis: 2009-2022.” PEDIATRICS, 10 Sept. 2024, publications.aap.org/pediatrics/article-abstract/154/4/e2024066879/199331/Rotavirus-Vaccine-Effectiveness-Against-Severe?redirectedFrom=fulltext, https://doi.org/10.1542/peds.2024-066879.

2. CDC. “Clinical Overview of Rotavirus.” Rotavirus, 18 June 2024, www.cdc.gov/rotavirus/hcp/clinical-overview/index.html. 

3. Dodet, B, et al. “Rotaviruses in Human and Veterinary Medicine.” Sante (Montrouge, France), vol. 7, no. 3, 1997, pp. 195–9, pubmed.ncbi.nlm.nih.gov/9296811/.

4. Lin, L H, et al. “Breath Hydrogen Test for Assessment of Lactose Malabsorption Following Rotavirus Gastroenteritis.” Journal of the Formosan Medical Association = Taiwan Yi Zhi, vol. 89, no. 12, Dec. 1990, pp. 1072–6, pubmed.ncbi.nlm.nih.gov/1982676/. 

5. Mayo Clinic. “Lactose Intolerance.” Mayo Clinic, 5 Mar. 2022, www.mayoclinic.org/diseases-conditions/lactose-intolerance/symptoms-causes/syc-20374232. 

6. MedlinePlus. “Lactose Intolerance: MedlinePlus Genetics.” Medlineplus.gov, 18 Aug. 2020, medlineplus.gov/genetics/condition/lactose-intolerance/. 

7. Ramig, Robert F. “Pathogenesis of Intestinal and Systemic Rotavirus Infection.” Journal of Virology, vol. 78, no. 19, 14 Sept. 2004, pp. 10213–10220, www.ncbi.nlm.nih.gov/pmc/articles/PMC516399/, https://doi.org/10.1128/jvi.78.19.10213-10220.2004.

8. “Rotavirus Infections | Boston Children’s Hospital.” Childrenshospital.org, 2025, www.childrenshospital.org/conditions-treatments/rotavirus-infections.

9. Shen, Jilu, et al. “Rotavirus Regulates the Gut Microhabitat Immune Response through the IL-22/PSTAT3/RegIIIγ Signaling Pathway, Leading to Lactose Intolerance.” International Immunopharmacology, vol. 150, 15 Feb. 2025, p. 114275, https://pubmed.ncbi.nlm.nih.gov/39954663/ 

10. Ye, Qian, et al. “Fecal Gut Microbiome Alterations and Its Association with Lactose Intolerance in Children with Rotavirus Infection-Related Diarrhea.” European Journal of Pediatrics, vol. 184, no. 9, Summer 2025, p. 553, pubmed.ncbi.nlm.nih.gov/40813488/, https://doi.org/10.1007/s00431-025-06398-w.