Is B12 useful for fatigue?

Whether vitamin B12 helps with fatigue depends on your baseline levels. A deficiency can cause fatigue, weakness, and brain fog – common in vegans, older adults, or those with gut issues. Supplementation then often improves energy. However, if you already have adequate B12, extra doses rarely provide additional benefit. Evidence is moderate: benefits are clear only in deficiency. A blood test (e.g., holotranscobalamin) can confirm your status. MyBody-X offers home blood tests, but results should be reviewed by a doctor. Caveat: high-dose B12 without deficiency is unnecessary and may mask other conditions.