Evidence check: LCT in the context of Müdigkeit

The question of LCT (lactase gene) in the context of fatigue is indirect. LCT variants (e.g., rs4988235) determine lactase persistence and thus the ability to digest lactose. In lactose intolerance, symptoms like bloating, abdominal pain, and diarrhea can occur, which may secondarily lead to fatigue due to disturbed sleep or nutrient deficiencies (e.g., calcium). However, fatigue is a highly nonspecific symptom. The evidence for a direct causal link between LCT genotype and fatigue is weak. No high-quality studies have examined fatigue as a primary endpoint in lactose intolerance. The MyBody-X DNA test can determine the genotype, but interpretation should be cautious: a risk allele does not guarantee symptoms. A lactose intolerance breath test (hydrogen test) is more clinically actionable. Conclusion: LCT may play a role in fatigue if gastrointestinal symptoms are present, but overall evidence is weak to moderate.