Can primary hypolactasia manifest itself after the age of 20 years? A two-decade follow-up study.

OBJECTIVE: The age at manifestation of primary hypolactasia varies between ethnic groups. Many people report experiencing the first symptoms of lactose intolerance at adult age. The purpose of this study was to investigate whether primary hypolactasia can appear after the age of 20 among the Finnish population and to investigate the outcome of different diagnostic methods of lactose maldigestion.

MATERIAL AND METHODS: Lactose digestion status was assessed by the lactose tolerance test with ethanol (LTTE) in 42 subjects (38-71 years) who reported having gastrointestinal symptoms after the ingestion of 20 g or less of lactose and who were diagnosed as lactose digesters in earlier studies. Thirteen of the study subjects underwent upper gastrointestinal endoscopy, and 35 gave a blood sample for DNA analysis.

RESULTS: Only one of the 42 subjects studied had the genotype C/C(-13910) indicating hypolactasia. Lactase activity was higher in those with the genotype T/T (69.2 U/g protein) than in those with the heterozygous genotype C/T (36.3 U/g protein) (p=0.017).

CONCLUSIONS: Although primary hypolactasia normally appears before the age of 20 years, the decline in lactase activity may on rare occasions continue after that age. Genotyping of the C/T(-13910) variant was found to be a reliable diagnostic approach in defining the lactase persistence/non-persistence status of the study subjects.