Feeling tired is often blamed on too little sleep, too much work or the general pace of modern life. But a new study suggests nutrition status may be one more piece of the fatigue puzzle, especially when it comes to vitamin B12, folate and a blood marker called homocysteine.
The study, published in Nutrients, looked at about 600 healthy Japanese adults and found that people with higher homocysteine levels tended to have lower levels of vitamin B12 and folate. When researchers analyzed men and women separately, higher homocysteine was associated with greater physical fatigue in men and lower motivation in women.
The findings do not mean that B vitamins are a cure for tiredness. The study was observational, which means it can show a relationship but cannot prove cause and effect. Fatigue also can be shaped by many factors, including sleep, stress, workload, mental health, medication use, chronic illness and other nutrient deficiencies.
Still, the study adds an interesting layer to the conversation about how diet quality may affect how people feel day to day.
Homocysteine is an amino acid found in the blood. The body normally helps process it with support from several B vitamins, including vitamin B12 and folate, also known as vitamin B9. When B12 or folate status is low, homocysteine levels can rise.
Homocysteine has usually been studied in connection with cardiovascular disease, dementia and fractures. In this study, researchers wanted to know whether it might also be related to fatigue and motivation in generally healthy adults.
The team measured blood levels of homocysteine, folate and vitamin B12, then assessed fatigue and motivation using standard questionnaires. The researchers also accounted for several factors that could influence fatigue, including age, sleep duration, workload and dietary habits.
“This suggested relationship between vitamin B12, folate, and fatigue in healthy individuals may represent the first report of its kind,” said Professor Hiroaki Kanouchi of Osaka Metropolitan University.
The sex-specific findings were especially notable. In men, higher homocysteine levels were linked with greater physical fatigue. In women, higher levels were linked with lower motivation. The study does not explain why those patterns differed by sex, and more research would be needed to understand whether the relationship holds in other groups of people.
That distinction matters because fatigue is not one simple thing. Some people experience physical tiredness, while others describe low drive, mental fog or a lack of motivation. Those experiences can overlap, but they may not always have the same causes.
The study also should not be read as a reason to start taking high-dose supplements without guidance. Vitamin B12 and folate are essential nutrients, but fatigue is broad and nonspecific. Persistent or unexplained fatigue can sometimes point to a medical issue that deserves evaluation, including anemia, thyroid problems, sleep disorders, depression, infections or other health conditions.
A more practical takeaway is that dietary imbalance may be worth considering as part of the bigger fatigue picture. Vitamin B12 is found in animal-based foods and some fortified foods, while folate is found in foods such as leafy greens, beans, citrus fruits and fortified grains. People who eat little animal-based food, have certain digestive conditions or take medications that affect absorption may be more likely to need their B12 status checked.
Kanouchi said the findings suggest researchers may need to look beyond homocysteine’s better-known role in long-term disease risk.
“Blood homocysteine levels have traditionally raised concerns in relation to cardiovascular disease, dementia, and fractures,” Kanouchi said. “However, our findings suggest that attention should also be paid to fatigue and motivation in the future. To prevent an increase in homocysteine levels, it is important to avoid deficiencies in vitamin B12 and folate. Maintaining a well-balanced diet on a daily basis is essential.”
The authors reported that the research received no external funding. Three authors, E.N., Y.N. and T.N., are employees of Alinamin Pharmaceutical Co. Ltd.