Vitamin C (ascorbic acid, in more formal terms) is a well-known antioxidant that may be good for fighting off depression, not just the common cold as many would believe. The relationship between vitamin C and depression has only recently been established scientifically, but it has been a strong one.
Studying vitamin C deficiencies is quickly becoming more common in the scientific realm due to the fact that contemporary diets (high in convenience, fast foods) are reducing the amount of time that people spend preparing and eating fresh foods, thus causing vitamin deficiencies which affect cognition and behavior. In fact, vitamin C deficiencies have been established in the community at large, the hospitalized elderly, and college students. Such findings are a cause for concern due to the negative impacts that emerge as a result of vitamin C deficiency.
In this article, we will review the relationship between vitamin C, depression, cognitive states such as memory, and relationships to other conditions, as well as relevant animal models and experimental mazes which are commonly used in research.
Vitamin C, Depression, and Chronic Stress
Mental or emotional states such as depression or anxiety have been receiving a lot of scientific attention lately, especially the interplay between vitamin C and depression.
A group of researchers used a vitamin C deficiency animal model, gulo -/- mice, and studied the subsequent behaviors that emerged. Gulo -/- mice are used to study vitamin C deficiency because they do not have the gene that produces the protein (gulonolactone oxidase) which is involved in the last step of ascorbic acid synthesis. So, gulo -/- mice need to acquire vitamin C through dietary intake and if they have a diet restricted in vitamin C, they become vitamin C deficient.
The three conditions that were included in the researchers’ experiment were:
- A control group, C57Bl/6J wild-type mice
- The control gulo -/- mice, fed a regular diet
- The experimental gulo -/- mice, on a diet deficient of ascorbic acid
The researchers included two control groups in order to be able to compare their behavioral differences which might exist even though both came from similar genetic backgrounds. Such considerations are important because animal strains can show subtle differences in behaviors which may, in turn, affect results during statistical analysis. For example, in this experiment, the wild-type control mice traveled less distance in the Elevated Zero Maze than the control gulo -/- group did. Although the control groups remained similar in other parameters of the Elevated Zero Maze, such as the time spent in closed zones, the effect of controls is still an important consideration to take into account when designing animal studies.
The researchers interpreted that the vitamin C deficient mice had depressive symptoms given their results in the Tube Dominance Test, an apparatus that is designed to measure winning conflict situations and social hierarchy. The vitamin C deficient mice had the shortest trial times, indicating that they were submissive and backed out of the situation quickly. Furthermore, even when the vitamin C deficient mice were given ascorbic acid (later on, in an attempt to “resuscitate” them), their trial length did not increase and the researchers concluded that this was a form of depression, specifically behavioral despair.
Behavioral differences were supplemented by biological alterations in the animals’ brain. The vitamin C deficient mice had more oxidative damage in the proteins and lipids found in the cortex. Also, the cortex and striatum had decreased levels of serotonin and dopamine metabolites which, with a more longitudinal experimental design, might have triggered more behavioral problems to emerge.
In a different experiment, also aiming to study the interaction between vitamin C and depression, researchers induced depression mice via the chronic unpredictable stress model. The chronic unpredictable stress model (CUS) was constructed to mimic the environmental factors that contribute to the formation of depression and has a strong face, construct and predictive validity.
The researchers wanted to explore the relationship between vitamin C, depression, and chronic stress in mice by running behavioral and biochemical tests after inducing CUS and treating it. They paid particular attention to reactive oxygen species because chronic stress has been shown to increase the amount of reactive oxygen species available in the brain. Furthermore, depression has been linked to related biomarkers of oxidative stress, as demonstrated by studies that have examined depressed patients’ lipid peroxidation levels and blood levels of circulating antioxidant enzymes.
The untreated CUS mice exhibited increased immobility during the Tail Suspension Test, an effect that was reversed in the group of mice that had CUS-induced depression but were treated with ascorbic acid. In fact, the ascorbic acid treated group performed at the level of the CUS-induced group that was treated with fluoxetine, a commonly administered antidepressant drug. Reducing immobility in the Tail Suspension Test is a significant finding because increased immobility is a behavioral marker for depression in animal studies. Therefore, the researchers were able to conclude that vitamin C is able to reduce some of the problems associated with depression.
During the biochemical analysis, CUS-induced mice that did not receive treatment showed increased lipid peroxidation levels, as established by measured produced levels of thiobarbituric acid reactive species (TBARS) in both the hippocampus and the cerebral cortex. However, ascorbic acid treatment in the CUS-induced depressed mice was associated with a significant decrease in the hippocampus’ TBARS levels, a sign of decreased lipid peroxidation. The fluoxetine group, on the other hand, showed decreases of TBARS levels in the cerebral cortex.
The behavioral and biochemical profiles acquired from this experiment contribute to the growing body of knowledge that vitamin C and depression are related. However, further research needs to occur, in order to unravel the mechanisms and extent to which vitamin C can affect both mood and behavior.
Long-term Vitamin C Intake is Anxiolytic and Enhances Memory
In addition to understanding how vitamin C affects cognition and behavior, researchers are trying to establish how cognition and behavior are impacted by prolonged vitamin C supplementation.
Such findings have also been extended to the human population. In one study, focusing on biological and behavioral outcomes of prolonged vitamin C supplementation, healthy adults receiving vitamin C supplements for two weeks exhibited different physiological reactions to an environmental stressor than the control group did as revealed by reduced blood pressure and salivary cortisol levels.
One group of researchers set out to study the behavior of long-term vitamin C supplementation in rats. Their experiment lasted for 8 weeks and rats were divided into 3 groups, receiving different dosages of ascorbic acid, either 61, 114, or 160 mg/kg/day, in their water. Animals were subjected to behavioral testing, in order to establish behavioral differences across conditions.
In the Open Field Test, anxiolytic effects were noted in for the lower dosages of vitamin C. The rats that were on 61 mg/kg and 114 mg/kg supplementation schedules had lower frequencies of grooming, higher frequencies of walking, and higher frequencies of rearing. This particular profile of behaviors indicates that the rats were not as anxious as typically animals are during the Open Field Test. Also, the rats from these two dosage groups more frequently occupied the open arms in the Elevated Plus Maze, meaning that they were not anxious of open spaces as animals typically are. Also, statistically, the females spent the most amount of time in the open arms of the Elevated Plus Maze, indicating gender differences in behavior.
In the Novel Object Recognition task, the rats receiving the highest dosage of vitamin C, 160 mg/kg, explored the novel object to a greater extent than the controls did. The researchers concluded that the highest dosage of vitamin C led to an enhancement of recognition and memory abilities.
Overall, the researchers interpreted their results to mean that the long-term lower dosages of vitamin C (61 mg/kg and 114 mg/kg) induced anxiolytic effects in the rats and that the highest dose was responsible for bringing about enhanced memory effects.
Vitamin C Reduces Anesthesia-Related Cognitive Deficits
Cognitive deficits are a known and dangerous side-effect of anesthesia given out to patients in need of surgery. However, vitamin C may be promising in ameliorating the cognitive problems associated with anesthesia.
One study set out to examine the effect of anesthesia on obesity by using an animal model. Obesity was of special interest due to the fact that many more children than ever before are needing surgery as a result of obesity-related problems. Therefore, the researchers set out to determine what affect anesthesia would have on cognition and whether these issues can be lessened through vitamin C supplementation.
Anesthesia is commonly induced through the administration of halogenated ethers (such as isoflurane, desflurane, and sevoflurane) which can be used alone or combined with other drugs. The precise mechanisms of anesthesia remain unknown, but there are some known mechanisms, such as the fact that anesthesia has been shown to affect the g-aminobutyric acid type A and N-methyl-d-aspartate glutamate receptors. These receptors are believed to be crucial for the healthy development of the mammalian brain. Therefore, the fact that an increasing amount of children will be in need of anesthesia as a result of obesity-related surgery is a cause for concern as the procedure may in the future impact their cognitive skills, behavior, and development.
To test the effect of anesthesia on cognitive function, the researchers employed a Morris Water Maze which is a commonly used maze for assessing spatial working memory. The researchers found that the mice that were previously exposed to anesthesia needed a significantly longer amount of time to get to the hidden platform than the control mice receiving no anesthesia. Furthermore, diet affected results. The high-fat diet group exposed to anesthesia needed significantly more time than the mice that were on a normal diet. However, in the other experimental groups that were supplemented with vitamin C (in addition to anesthesia exposure), the time to reach the hidden platform was significantly decreased regardless of diet group. Also, vitamin C supplementation, regardless of condition, was associated with increased time spent in the target quadrant. Such behavioral results indicate that vitamin C may be a beneficial supplement to take, in order to buffer against the cognitive deficits associated with anesthesia which were further amplified by a high-fat diet.
In terms of biochemistry, anesthesia exposure was associated with the physical markers of increased levels of plasma S100β, a protein released in the extracellular matrix when a tissue has been damaged or injured. Also, caspase-3 levels, a known marker for establishing neuronal death from apoptosis, were measured in the hippocampus (with a special focus on CA1, CA3, and the dentate gyrus). Both caspase-3 and S100β levels were significantly higher as a result of anesthesia exposure, but these levels were further exacerbated if the mice were on a high-fat diet. Vitamin C supplementation was associated with a significant drop in S100β and caspase-3 levels, regardless of condition.
Since physical markers associated with cell death and damage were even more severe and pronounced in the mice that fed the high-fat diet, this could have implications for the human population. It is possible that patients that are obese, including children, could face many problems if receiving anesthetics while on a high-fat diet. Vitamin C could prove to be a beneficial supplement to take, protecting both the brain and cognition.
Vitamin C Deficiency Accelerates Aging and Amyloid Formation
In order to determine how vitamin C deficiency affects development and pathogenesis, a group of researchers chose to focus on vitamin C deficiency in the context of normal aging and Alzheimer’s disease.
The researchers used the APPSWEPSEN1deltaE9 mouse which is the animal model for Alzheimer’s disease and crossed it with SVCT2+/- mice, in order to induce vitamin C deficiency. SVCT2+/- mice have a decreased amount of sodium-dependent vitamin C transporter necessary for neuronal transport of vitamin C in the brain. By crossing this breed with APP/PSEN1+ bigenic mice, the researchers are able to induce vitamin C deficiency while subsequently studying its effects on aging and Alzheimer’s disease pathogenesis.
To examine behavioral and subtleties across conditions, the researchers divided the mice into various groups, including: the wild-type control mice, the APP/PSEN1+ mice (the Alzheimer’s model), the SVCT2+/- mice (the vitamin C deficiency model), and the APP/PSEN1+/SVCT2+/- mice (combined models of both Alzheimer’s and vitamin C deficiency).
In the Rotarod Test, neuromuscular ability and procedural learning are measured. The test is administered over the span of two days and the mice are expected to perform better on the second day than on the first day, a marker of procedural memory. Although all mice performed better on the second day, regardless of cognition, the vitamin C deficient mice still showed impairments compared to the improvement that was typical for the control group. The researchers interpreted this to be possibly due to the muscular weakness associated with age and potentially due to the neuronal changes occurring at the level of the neuromuscular junction.
Group differences were observed in the Y-Maze, a maze frequently used by scientists to assess spatial working memory. The researchers found that the number of arm entries was found to significantly decrease with age, with the largest decrease being 37% fewer entries in the APP/PSEN1+ group. The fact that the Alzheimer’s mice without vitamin C supplementation performed worse on the Y-Maze signifies that vitamin C may have neuroprotective effects in the brain.
In terms of biochemical findings, the young mice that were only vitamin C deficient revealed to have the same oxidative stress markers in the brain as the mice in the Alzheimer’s APP/PSEN1+ condition, namely: malondialdehyde, F2-isoptrostanes, and protein carbonyls. Such findings indicate the molecular similarities between a serious neurodegenerative disease and vitamin C deficiency. Furthermore, the mice that had Alzheimer’s disease and were deficient in vitamin C had greater concentrations of amyloid-β plaque deposits in the cortex and hippocampus than the Alzheimer’s group that had adequate levels of vitamin C.
The robust knowledge available on vitamin C and depression, as well as other cognitive functions such as memory, needs to be further unraveled and studied.
Furthermore, the interaction between vitamin C and other diseases should be explored. For example, one relatively new avenue of research has been the intersection between vitamin C and Huntington’s disease. Another research area that is expanding deals with the relationship between vitamin C and Alzheimer’s disease, since vitamin C has been shown to ameliorate the oxidative stress that induces such neurodegenerative disease. Future directions also include the study of vitamin C, depression, and anxiety in conditions such as anorexia nervosa.
Also, more longitudinal experimental designs are necessary, in order to investigate the prolonged effects of vitamin C deficiency (or supplementation) on various facets of behavior. Regardless of the area of research, there is much future and potential in studying the mechanisms and interactions between vitamin C, behavior, and cognition.
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