Evidence check: MTHFR in the context of sleep

The claim that MTHFR variants (e.g., C677T) directly affect sleep is weakly supported by evidence. The mechanism is plausible: MTHFR is involved in methylation, which influences neurotransmitter synthesis (serotonin, melatonin) and homocysteine metabolism. Some studies report associations between MTHFR polymorphisms and sleep quality, insomnia, or sleep duration, but effect sizes are small, inconsistent, and often not replicated. Most data come from cross-sectional studies or GWAS with low effect sizes. Direct-to-consumer DNA tests often overstate this link. Clinically relevant sleep disorders are usually multifactorial (stress, hormones, lifestyle). An MTHFR test alone does not provide reliable guidance. If homocysteine is elevated, methylfolate supplementation may be considered – but that targets general metabolism, not sleep specifically. Evidence: mechanistic/weak. Sources: none directly from provided context.