Low B12 and Folate Linked to Fatigue in Men and Low Motivation in Women, Study Finds

Deficiencies in vitamin B12 and folate are linked to chronic fatigue in men and reduced motivation in women, according to a study published in the journal Nutrients in May 2026. Researchers at Osaka Metropolitan University found that elevated homocysteine levels, a blood marker that rises when these vitamins are lacking, correlated with physical exhaustion in men and lower motivation in women.

The study enrolled approximately 600 healthy Japanese adults and used the Chalder Fatigue Scale and a Visual Analog Scale to measure energy and motivation levels. Researchers also measured plasma concentrations of homocysteine, folate, and vitamin B12.

Higher homocysteine levels were significantly associated with increased physical fatigue in men, while women with elevated homocysteine reported lower motivation. The findings held after adjusting for age, sleep duration, workload, and dietary habits.

"When these vitamins are insufficient, the body's ability to convert food into energy is compromised," said Professor Hiroaki Kanouchi, who led the research team. "This can show up as exhaustion, mental fog, and reduced stamina."

Vitamin B12 and folate are essential for red blood cell production, DNA synthesis, and neurological function. Both are found in animal products, leafy greens, and legumes. Deficiencies are common in people who follow restrictive diets, older adults, and those with certain digestive conditions that limit nutrient absorption.

The study is cross-sectional, meaning it captures a snapshot in time rather than tracking participants over a period. Researchers say the findings are hypothesis-generating and do not prove direct causation. They recommend that people with persistent fatigue consult a doctor and request blood tests to check their B12 and folate levels before starting supplements.

Experts advise that a diet rich in eggs, dairy, lean meats, leafy greens, and legumes is the best way to maintain adequate B-vitamin levels for most people.