Can LCT help with fatigue?

LCT encodes lactase, the enzyme that digests lactose. There is no direct, evidence-based link between LCT variants and fatigue. However, lactose intolerance (often due to LCT polymorphisms like rs4988235) can cause bloating, diarrhea, and malabsorption of nutrients such as calcium and vitamin D. These symptoms may indirectly contribute to fatigue, especially if chronic. The evidence is mechanistic, based on physiological plausibility, not on clinical trials with fatigue as an endpoint. Other causes like iron deficiency, sleep disorders, or thyroid issues are far more common. A genetic test for LCT alone is not suitable to explain or treat fatigue. If lactose intolerance is suspected, a breath test or elimination diet is more informative.