Constant Fatigue? The Cause May Lie in Vitamin Deficiencies

Are you constantly tired, lacking energy and motivation, even after sleeping well? Scientists have discovered that low levels of important vitamins may be linked to the problem. A simple blood test can reveal surprising clues about the origin of your fatigue.

Feeling tired from time to time is normal. But when fatigue becomes constant, even after a good night's sleep, it can affect work, relationships, concentration, and quality of life.

Many people attribute this tiredness to stress or a hectic routine, but scientists are investigating whether certain biological changes in the body may play an important role in this problem. A new study analyzed the relationship among fatigue, motivation, and a blood-borne substance called homocysteine.

Homocysteine ​​is naturally produced by the body during protein metabolism. Under normal conditions, it is rapidly recycled and converted into other useful molecules through the action of B vitamins, especially folic acid, vitamin B12, and vitamin B6.

When these vitamins are at insufficient levels, homocysteine ​​can accumulate in the blood. Previous studies had already associated elevated levels of this substance with cardiovascular problems, cognitive changes, and depression. Now, researchers wanted to find out if it could also be related to persistent fatigue and lack of motivation.

To investigate this hypothesis, scientists analyzed data from 602 healthy adults living in the community. All participants underwent blood tests to measure levels of homocysteine, folic acid, and vitamin B12. They then answered validated questionnaires to assess different aspects of physical fatigue, mental fatigue, and daily motivation.

The researchers divided the participants into groups according to their homocysteine ​​levels and compared the results, taking into account factors that can also influence fatigue, such as age, lifestyle, and other health indicators.

The results showed an interesting association. Men with higher homocysteine ​​levels experienced more symptoms of physical fatigue than those with lower levels. Among women, the pattern was different: higher homocysteine ​​levels were associated with lower motivation.

Furthermore, both men and women with higher blood homocysteine ​​levels had lower levels of folic acid and vitamin B12, essential nutrients for various brain and metabolic functions.

Researchers believe this relationship may involve brain function. Elevated homocysteine ​​can interfere with processes important for the production of neurotransmitters such as dopamine and serotonin, substances involved in motivation, mood, mental energy, and well-being.

When these systems function inadequately, some people may experience increased fatigue, difficulty concentrating, and reduced energy for daily activities.

Despite the promising results, the authors themselves emphasize that the study does not prove that homocysteine ​​or vitamin deficiencies directly cause fatigue. The research only found an association between these factors.

Further long-term studies will be needed to confirm whether correcting B vitamin deficiencies or reducing homocysteine ​​levels can actually help combat chronic fatigue. Even so, the findings reinforce the importance of investigating possible nutritional deficiencies when persistent fatigue has no apparent cause.

READ MORE:

Associations of Plasma Homocysteine Reflecting Vitamin B12 and Folate Status with Fatigue-Related Outcomes in Healthy Adults

Hiroaki Kanouchi, Ayaka Yamamoto, Akiko Kuwabara, Shigeo Takenaka, Eiji Nishikubo, Yukihiro Nomura, Takehiro Naruto, Kyosuke Watanabe, Kei Mizuno, and Yasuyoshi Watanabe 

Nutrients. 16 March 2026, 18(6), 941; DOI: 10.3390/nu18060941

Abstract: 

Background/Objectives: Fatigue and reduced motivation impair daily functioning and quality of life. Homocysteine (Hcy) has been implicated in oxidative stress and one–carbon metabolism, but its relationship with fatigue–related outcomes remains unclear. We explored associations between plasma Hcy and fatigue-related measures in healthy adults. Methods: We analyzed cross–sectional data from 602 community–dwelling adults. Plasma Hcy concentrations were categorized into sex−specific tertiles. Fatigue and motivation were assessed using the Chalder Fatigue Scale and a visual analog scale (VAS). Sex−stratified multivariable linear models adjusted for lifestyle and biochemical covariates were used to examine associations. Sensitivity analyses additionally modeled Hcy as a continuous variable. Results: Higher Hcy tertiles were associated with lower serum folate and vitamin B12 concentrations in both sexes (p < 0.001). In men, the lowest Hcy tertile was associated with lower Chalder physical fatigue scores, whereas in women the highest Hcy tertile was associated with lower VAS motivation scores in multivariable analyses. Pairwise contrasts indicated higher physical fatigue in men in the highest tertile compared with the lowest (T3–T1: 1.55; 95% CI 0.24–2.86; p = 0.022) and lower motivation in women (T3–T1: −5.62; 95% CI −10.65 to −0.59; p = 0.029). However, no significant associations were observed when Hcy was modeled as a continuous variable. Conclusions: In this exploratory cross−sectional analysis, plasma Hcy showed associations with fatigue−related outcomes in sex−stratified analyses. These findings should be interpreted cautiously and considered hypothesis–generating. Longitudinal and mechanistic studies are needed to clarify potential causal relationships.