High-dose vitamin C supplements can improve mood and gut microbiota in young adults

The relationship between diet, gut flora, and mental health has received increasing attention in scientific circles. A study published in Brain, Behavior, and Immunity shows that high-dose vitamin C supplements when taken to correct a deficiency can improve mental vitality and mood in healthy individuals. The authors describe how vitamin C supplementation influences the gut microbiota, and how the balance of the gut flora is closely linked to mood through the so-called gut–brain–immune axis.

Vitamin C is essential for both physical and mental health. There is also growing evidence that vitamin C plays a role in cognitive function, alertness, and the energy needed to cope with everyday challenges. Human studies have demonstrated that vitamin C supplements or higher dietary intake from citrus fruits, vegetables, berries, and herbs can reduce fatigue and improve mood.
It is well known that vitamin C is crucial for connective tissue, including connective tissues in the brain, and that it functions as an antioxidant that protects nerve cells from damage caused by free radicals and oxidative stress. Evidence also suggests that vitamin C affects brain function through additional physiological pathways involving neurological and immunological activity.
Gut flora is likewise essential for general health, as beneficial intestinal bacteria produce enzymes, neurotransmitters such as serotonin, and other important compounds. The gut flora also harbors potentially harmful bacteria and fungi that can cause imbalances and disease if they are not kept in check by beneficial microorganisms. For good health, the gut flora needs to remain in balance. This is a state known as symbiosis.
There is also a close link between the gut microbiota and the central nervous system (CNS) through the gut-brain axis.
A number of studies have shown how vitamin D, selenium, and other nutrients can influence mental health via this axis. However, until recently, no studies had examined the role of vitamin C in the gut-brain axis where immune capacity also plays a role.

Vitamin C influences mental health through several mechanisms

The new study included a group of healthy young adults (aged 20-39) who had suboptimal vitamin C levels in their blood (below 50 µmol/L). The researchers analyzed the participants’ gut flora using a specific rRNA technique. The volunteers were then divided into two comparable groups: one group received 500 mg of vitamin C daily for four weeks, while the other group received a placebo.
Before the intervention, their mental vitality, work capacity, and cognitive abilities were assessed using a Stroop test. Levels of BDNF (brain-derived neurotrophic factor) - a protein important for nerve cell function, growth, and survival - were measured. Blood levels of cytokines, white blood cells, and neurotransmitters were also analyzed using various methods.
Compared with the placebo group, the vitamin C group achieved the following:

• Increase in beneficial gut bacteria such as Bacillaceae and Anaerotruncus
• Decrease in Desulfovibrio bacteria, which in excess are associated with inflammatory conditions
• Decrease in Desulfovibrio bacteria, correlating with improved Stroop-test performance and cognitive function
• Decrease in Desulfovibrio bacteria, associated with increased BDNF levels and improved work engagement
• Reduction in cytokines and inflammatory responses, where excessive activity can damage nerve cells and impair neurotransmitter production

The researchers conclude that higher vitamin C intake can regulate the gut microbiota, in particular by reducing an overabundance of Desulfovibrio bacteria that is linked to reduced chronic inflammation and improved mental vitality and well-being.
The study therefore sheds new light on how higher vitamin C supplementation can enhance mental health through the gut-brain-immune axis.

Widespread vitamin C deficiency and our real needs

Ultra-processed foods lacking fruits and vegetables contribute to widespread vitamin C deficiency. Although outright deficiency and the classic disease scurvy (below 11 µmol/L) are rare, many people suffer from subclinical scurvy with suboptimal blood levels (below 50 µmol/L). Subclinical scurvy can cause easy bruising, bleeding gums, and recurrent infections. As the study shows, it may also lead to fatigue, cognitive impairment, reduced work capacity, and poorer mood.
The official daily recommendation for vitamin C is 80 mg. However, the requirement may be higher during infections, smoking, stimulant use, or various forms of stress. In the study, participants received 500 mg per day. Stronger supplements also exist, and they should ideally be non-acidic to avoid stomach discomfort.

Reference:

Minju Sim et al. Gut microbiota links vitamin C supplementation to enhanced mental vitality in healthy young adults. Brain, Behavior, and Immunity 2025