Vitamin C, or ascorbic acid, is absolutely essential for brain health, blood flow, and immunity. Should you supplement? Read on to find out.
What is Vitamin C?
Definition
Vitamin C (ascorbic acid) is an essential water-soluble micronutrient that has had a dramatic influence on world history. Naval and sea battles have literally been won and lost based on the numbers of the naval forces sick with scurvy (severe Vitamin C deficiency) [1].
Vitamin C is the most effective antioxidant in our blood, due to its water-solubility and to the wide range of radical oxygen species (ROS) that it can scavenge [1, 2].
Early research suggests that it is great for a whole range of health issues, like high blood pressure, stroke, cancers, atherosclerosis, inflammation and obesity [3, 4].
In this article, we will take you through exactly what the science says Vitamin C could do for your health.
Also, have in mind that vitamin C supplements have not been approved by the FDA for medical use. Supplements generally lack solid clinical research. Regulations set manufacturing standards for them but don’t guarantee that they’re safe or effective. Speak with your doctor before supplementing.
Snapshot
Proponents:
- Helps prevent colds & flu when the body is stressed
- Very safe
- A lot of people find high dose vitamin C very good for immunodeficiency, chronic toxin or infectious problems
- Anti-oxidant and anti-inflammatory
- Good for mood
- Supports skin & bone health
- Good for a wide array of conditions, including histamine intolerance
- High doses being researched for anti-cancer effects (still unproven)
Skeptics:
- May cause kidney stones
- Can cause nausea or stomach upset
- Can cause loose stools if too much is taken
- A number of purported benefits insufficiently researched
Vitamin C Function
Overview
Vitamin C is an essential nutrient and antioxidant with a number of important functions in the body. As such, vitamin C deficiency can produce serious symptoms.
Vitamin C is extremely important as an antioxidant owing to its ability to neutralize oxygen and nitrogen-based radicals, and because it also recycles both vitamin E and BH4 (tetrahydrobiopterin), which have key antioxidant and enzyme cofactor functions [1].
Vitamin C contributes to many important enzyme reactions, including those leading to the synthesis of norepinephrine, carnitine, cholesterol, amino acids, and several peptide hormones [5].
Because of its structural similarity to glucose, Vitamin C can replace glucose in many chemical reactions, and it can prevent the non-enzymatic glycosylation of proteins [2].
Brain Health
Image taken from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4179190/figure/nutrients-06-03818-f001/
As proof of the importance of Vitamin C for brain health, the brain retains Vitamin C at the expense of other tissues during chronic states of deficiency and can uphold concentrations 100-fold higher than other organs, e.g. liver and kidney [6, 7].
Vitamin C plays a role in many important functions in the brain, including reactive oxygen species scavenging, neuromodulation, and the development of new blood vessels (angiogenesis) [6].
Vitamin C modulates neurotransmitter systems of the brain (cholinergic, catecholaminergic, and glutamatergic) [6].
Vitamin C helps the general development of neurons through maturation, differentiation and myelin formation [6].
Vitamin C helps to maintain the integrity and function of several processes in the vascular system [6], which helps brain function.
Vitamin C participates in neuronal maturation and myelin formation (the electrically insulating layer around nerves) and is also involved in transmitting signals through the nervous system via neurotransmitters [6].
Vitamin C also prevents neuronal damage [6].
Vitamin C induces the expression of brain-derived-neurotrophic-factor (BDNF), contributing to the defense mechanisms of the brain [6].
Mitochondrial Health
Vitamin C stimulates mitochondrial function, by decreasing ROS generation, stimulating the activity of manganese superoxide dismutase/SOD2 and glutathione peroxidase, and modifying the activity of the electron transport chain [8].
Vitamin C protects the mitochondrial membrane and DNA against oxidative damage [9].
Collagen Production
Stabilization of collagen by Vitamin C is critical to forming the connective tissue framework of the entire body; including skin, bones, cartilage, tendons, ligaments, and blood vessels [5].
The final steps of collagen production depend on Vitamin C (Vitamin C acts as an electron donor in the hydroxylation of procollagen prolyl and lysyl residues) [6].
Vitamin C deficiency disrupts collagen maturation, leading to impaired integrity of the blood vessel wall, hemorrhage, and cerebral bleedings in mice [6].
Bone Health
Vitamin C is essential for normal bone development [10].
In humans, there is a positive relationship between Vitamin C levels and bone health, indicated by bone mineral density, fracture probability, and bone turnover markers [11].
Vitamin C-deficient animals show impaired bone health and decreased bone formation. Vitamin C supplementation was able to prevent bone loss in several animal models [11].
Vitamin C deficiency plays an important role in spontaneous bone fracture by inhibiting bone cell differentiation and promoting the transition of bone cells into fat cells in mice [12].
Daily use of Vitamin C supplements, along with estrogen replacement therapy and calcium supplements, can help increase bone mass in postmenopausal women [13, 14].
Higher Vitamin C intakes were associated with a lower risk of osteoporosis in Korean adults aged over 50 with low levels of physical activity [15].
In addition to stabilizing collagen in the bone matrix [11], Vitamin C also scavenges free radicals detrimental to bone health [11].
Skin Health
Vitamin C contributes to the maintenance of healthy skin [16].
Applied to the skin, topical Vitamin C is highly efficient as a rejuvenation therapy, inducing significant collagen synthesis with minimal side effects [17].
Topical Vitamin C can partially correct structural changes associated with the aging process [18].
Vitamin C is an effective short-term treatment for melasma and post-inflammatory hyperpigmentation [19].
Nutrient Availability
Vitamin C enhances the bioavailability of other nutrients, such as vitamin E and non-heme iron, which may enhance the health effects of Vitamin C-containing foods [20].
Lung Health
Levels of vitamin C in the lungs are up to 30 times higher than in the blood.
Vitamin C gets consumed while it protects against oxidants, indicating that even a single dose of vitamin C can be effective in protecting against acute increases in oxidative stress in the lungs [21].
Potential Benefits of Vitamin C Supplements
Effective For:
1) Scurvy
Vitamin C deficiency, or scurvy, presents with symptoms such as lethargy, anorexia, fatigue, weakness, and rash. As scurvy progresses, it may cause anemia, pain, easy bruising, gum disease, poor wound healing, and depression [22, 23, 24].
Vitamin C supplementation, as supervised by a medical professional, easily and efficiently reverses scurvy; likewise, a diet high in vitamin C or vitamin C supplementation will prevent the development of scurvy [22, 23, 24].
Possibly Effective For:
2) Mood Support
Based on the exisiting evidence, it’s possible that getting enough vitamin C supports healthy mood.
However, there is insufficient evidence to support the use of supplements in people with mental health disorders like anxiety and depression.
Emotional Balance
Long-term Vitamin C deprivation is linked to nervousness and emotional instability [1].
Vitamin C increases oxytocin release [25, 26].
There was a 35% reduction in mood disturbance in hospitalized patients following treatment with Vitamin C [27].
Another study found that Vitamin C supplementation does not have large effects on psychological performance, personality or current mental state, in young men (17-29 years) except in cases where supplementation corrects an existing deficiency [1].
Anxiety
Vitamin C reduced anxiety in high school students [28].
Short-term supplementation of Vitamin C was safe and beneficial for reducing anxiety levels in diabetic patients [29].
Depression
Many studies have found that Vitamin C may reduce the severity of depressive disorders in both children and adults, as well as improve the mood of healthy individuals [27, 25].
In a trial including depressed shift workers, Vitamin C significantly decreased depression severity [26].
Poor Vitamin C status is associated with increased symptoms of depression following an acute illness in older people [30].
Adequate Vitamin C levels are necessary for the conversion of the neurotransmitter dopamine to norepinephrine, an important hormone in depression and mood swings [31]; according to some researchers, this may explain why patients with Vitamin C deficiency present with symptoms of depression [30].
Vitamin C also increases the effectiveness of antidepressants [26]. Patients treated for six months with fluoxetine and Vitamin C showed a significant decrease in depressive symptoms compared to the fluoxetine plus placebo group [27].
Vitamin C deficient mice are less active [32].
3) Age-Related Cognitive Decline
Chronic low Vitamin C status in humans is associated with neurodegenerative disorders. However, no causal link has been established.[6].
Higher Vitamin C intake has been associated with better cognitive function in the elderly [1, 6].
Vitamin C levels were significantly lower in elderly people suffering from different kinds of dementia [6].
Supplementation with Vitamin C was associated with a reduced incidence of Alzheimer’s disease in humans [6].
Vitamin C injected for 3 consecutive days improved the learning and memory of aged mice [33].
In rodents, Vitamin C treatments countered the impaired memory caused by chronic sleep deprivation [34].
In animal models of Alzheimer’s disease, Vitamin C improved cognitive function [6].
However, in the aging brain, Vitamin C deficiency may impair cognitive function through reduced signal transduction, as well as amyloid β deposition resulting in a generation of reactive oxygen species and increased risk of Alzheimer’s disease [6].
If you are older and concerned about Alzheimer’s, talk to your doctor before supplementing with vitamin C.
4) Immunity & Common Cold Prevention
Many infections lead to reduced Vitamin C levels [35].
However, whether or not vitamin C can prevent or reduce the severity of infections, including the common cold, is a controversial topic. Although some studies have had mixed results, the majority of the evidence backs ups the benefits of supplementation.
Vitamin C increases the functioning of various white blood cell types and decreases the replication of viruses [35, 5].
Vitamin C reduced the duration and severity of the common cold [36, 37].
Vitamin C reduced the incidence of colds at times of extreme physical stress [31, 38].
Vitamin C reduced the incidence of pneumonia [38].
Vitamin C decreased the duration and severity of respiratory infections in male swimmers, but not in women [39].
Supplementary vitamin C promoted H. pylori eradication in 30% of patients receiving the supplement in addition to conventional therapy [40].
5) Inflammation
Vitamin C may reduce inflammation by inhibiting inflammatory cytokines [4, 41, 42].
Vitamin C alleviated inflammation in patients with obesity, diabetes, or high blood pressure [2].
High dose intravenous vitamin C may reduce inflammation (hs-CRP & inflammatory cytokines: IL-1α, IL-2 (Th1 Cytokine), IL-8, TNF) in cancer patients [43].
As mentioned above, Vitamin C may inhibit obesity-related inflammation, and therefore prevent obesity-related inflammatory diseases [3].
Vitamin C reduced oxidative stress and inflamatory response to artificially induced inflammatory bowel disease (IBD) (reduced inflammatory cytokines, (MPO) and malonaldehyde (MDA) activities) [41].
6) Exercise & Recovery (if Deficient)
Vitamin C increased physical performance and decreases oxidative stress, but only in those with an already low Vitamin C status [44].
Vitamin C decreased the levels of free radicals generated during exercise and attenuates oxidative stress [21].
Vitamin C prevented exercise-induced muscle damage, immune dysfunction, and fatigue [45, 46].
However, it is important to note that reactive oxygen species may actually control beneficial training adaptations that high doses of Vitamin C prevent from occurring [46, 47].
Insufficient Evidence For:
The following purported benefits are only supported by limited, low-quality clinical studies. There is insufficient evidence to support the use of vitamin C for any of the below-listed uses. Talk to your doctor before taking any kind of supplements, and don’t use vitamin C in place of something your doctor prescribes.
7) Histamine Levels
As vitamin C levels decrease, blood histamine levels tend to increase [48].
Oral and intravenous administration of vitamin C resulted in a reduction of blood histamine levels [48, 49].
Sea Sickness
Histamine is a potential causative agent of seasickness. People exposed to waves show increases in histamine levels.
Vitamin C is effective in suppressing symptoms of seasickness, particularly in younger individuals [50].
8) Sexual Health
Vitamin C is associated with higher levels of progesterone and follicle-stimulating hormone in healthy premenopausal women [51].
During Pregnancy
Some studies found that babies weighed more when they and their mothers had higher blood Vitamin C levels [52, 53].
In the developing brain of a baby, neuronal density and maturation are compromised by Vitamin C deficiency, giving rise to decreased brain volume [6].
An absence of Vitamin C is detrimental to survival in newborn mice. Furthermore, deficiency around birth reduced hippocampal volume and neuron number and cause decreased spatial cognition in guinea pigs [6].
Libido
In one study, high-dose Vitamin C improved mood and increased the intercourse frequency of 42 healthy adults [25].
Sperm Quality
Vitamin C improved sperm motility and structure in men [54].
9) Fatigue
Administration of high dose intravenous Vitamin C reduced fatigue in office workers [55].
Vitamin C delays fatigue in rats [56].
10) Blood Pressure
Vitamin C significantly lowered systolic and diastolic blood pressure in patients with mild-to-moderately high blood pressure [2].
11) Blood Flow
High-dose Vitamin C can prevent or restore impaired blood flow caused by reactive oxygen species (ROS), preserve the integrity of the blood vessel barrier, and strengthen antibacterial defenses [57].
Vitamin C helps to prevent blood vessel dysfunction, stimulate collagen synthesis, and enhances cell proliferation of blood vessel cells [5].
Vitamin C plays a positive role in reversing the earliest stages of hardening of the arteries [5].
Vitamin C deficiency may result in decreased blood vessel integrity, e.g. through decreased NOS generation and impaired synthesis of mature collagen. This might lead to increased plaque formation and the incidence of stroke [6].
12) Gut Health
Vitamin C may improve gut tolerability to aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) [58].
Vitamin C saves mice from irradiation-induced gut damage that is usually lethal [59].
13) Weight Management
People with adequate levels of Vitamin C burn 30% more fat during moderate exercise compared to subjects with low Vitamin C levels [3].
Vitamin C inhibits the fat accumulation of fat cells. Indeed, Vitamin C supplementation has been associated with bodyweight reduction and a massive reduction in the number of fat cells in rats and guinea pigs [3].
Eight weeks of Vitamin C supplementation in a cafeteria model of obesity protected rats against diet-induced fat storage and excess leptin [3].
Low Vitamin C levels are related to a high waist-to-hip ratio [3].
Vitamin C has been associated with a lower prevalence of obesity and with the prevention of weight gain in a 3-year follow-up study in adults [3].
Check out our complete post on weight loss here.
14) Diabetes
Vitamin C administration improved whole-body glucose disposal and non-oxidative glucose metabolism [3].
Reductions in glucose and insulin levels were much better in rats fed a high-fat diet supplemented with Vitamin C for 2 weeks, compared to those fed high fat alone [3].
Vitamin C protects against diabetic blindness, improves high-density lipoprotein-cholesterol (HDL-c), and improves blood vessel function [2].
Vitamin C may benefit patients with type 2 diabetes by decreasing blood glucose and lipids [60].
Vitamin C inhibits the production of cortisol/glucocorticoids which raise blood sugar [3].
15) Stroke
Brain Vitamin C concentrations increase during ischemia (inadequate blood supply) [6].
In rodents and primates, Vitamin C reduced the area of the brain deprived of blood supply during a stroke [6].
In humans, higher Vitamin C levels are associated with a lower likelihood of stroke [6].
16) Oxidative Stress in Smokers
People who smoke have lower levels of blood and cellular Vitamin C (and vitamin E) [5].
Vitamin C supplements of 500 mg twice daily for two weeks were sufficient to normalize the disappearance rate of vitamin E in smokers [5].
17) Detox
Vitamin C reduces the amount of persistent organic pollutants (POPs) in 15 adult women [61].
18) Postoperative Recovery
Blood Vitamin C concentrations fall after surgery, and a further decline in patients under surgical intensive care, due to an increased demand caused by increased oxidative stress [62].
In uncomplicated gastrointestinal surgery, continuous administration of Vitamin C reduced postoperative oxidative stress [62].
Post-operative atrial fibrillation (abnormal heart rhythm) was prevented after cardiac surgery by vitamin C supplementation [62].
Lacking Evidence For:
No clinical evidence supports the use of vitamin C for any of the conditions listed in this section.
Below is a summary of the existing animal and cell-based research, which should guide further investigational efforts. However, the studies listed below should not be interpreted as supportive of any health benefit.
19) Thyroid Health
In rats, low doses of Vitamin C stimulate the thyroid, whereas high doses inhibit thyroid activity [63].
20) Stress
Vitamin C inhibits the production of cortisol/glucocorticoids in guinea pigs, indicating a potential role in suppressing the stress response [3].
Cancer Research
There is no evidence to suggest that vitamin C prevents or treats cancer.
High-quality clinical trials are lacking, a large body of the exisiting evidence relies on animal data or association studies.
Reports suggest that high-dose Vitamin C has anticancer effects in a laboratory setting [64].
High-dose Vitamin C is more toxic to cancer than it is to normal cells and induces the death of various types of cancer cells, including mesothelioma, pancreatic, and leukemia cells [64].
High-dose Vitamin C suppresses tumor growth in animal models and tissue culture studies [64].
High dietary Vitamin C has been linked to reduced incidence of gastric cancer [65].
Higher dietary Vitamin C intake before breast cancer diagnosis was linked to increased survival rates. This association was strongest among women aged over 65 [66].
In one study, men with low Vitamin C levels were 62% more likely to die from cancer [67].
Vitamin C lowers pain and reduces the toxicity of some anticancer agents by reducing oxidative stress [55].
Intravenous Vitamin C alleviates a number of cancer- and chemotherapy-related symptoms, such as fatigue, insomnia, loss of appetite, nausea, and pain [68].
Vitamin C can reduce pain by 55% in radiotherapy patients with bone cancer [69].
Vitamin C can improve the quality of life of cancer patients, including reduced pain and the need for painkillers, both in the presence and absence of chemo- and radiotherapy [68].
Vitamin C Dosage
Recommended Daily Intake (RDA)
The current recommended daily intake for Vitamin C is 75 mg/day for women and 90 mg/day for men [1].
Amounts up to 125 mg/day are recommended for pregnant or lactating women, and an additional 35 mg per day to account for increased oxidative stress and vitamin C turnover in smokers [1].
Most animals can produce Vitamin C from glucose in the liver. However, humans have lost this ability and so an adequate, regular dietary intake is essential [3].
Vitamin C is needed in relatively high quantities since it is not retained nor accumulated in the body and the excess is immediately eliminated through urine [3].
The RDA for a given nutrient is calculated based on avoiding deficiency. Several sources now suggest that RDA should be as much as double the currently advised 75-125 mg per day depending on age, gender, pregnancy and smoking habits [1].
At Vitamin C intakes above 60 mg/d, vitamin C begins to appear in the urine. However, intakes of 250 mg/d and higher (approximately 400 mg/day) are required to saturate vitamin C concentrations in the blood and white blood cells [5, 1].
Tolerable Upper Intake Level
The ‘tolerable upper intake level’ is stated to be 2 g/day for adults. However, many people receive more than that in clinical settings, without suffering from apparent side effects [35].
Patients with pneumonia have received up to 100 g/day of Vitamin C without developing diarrhea, because of the changes in Vitamin C metabolism caused by the infection [35].
We strongly recommend against taking such large doses of vitamin C without the express recommendation and supervision of a doctor.
When the daily dose was increased from 200 to 2,500 mg, blood concentration increased from approximately 12 to 15 mg/L due to kidney clearance. Hence why some state that there is no justification for megadoses of vitamin C in healthy individuals [70].
Food-Derived vs. Synthetic Vitamin C
Most comparative bioavailability studies in humans have shown no differences between synthetic and natural Vitamin C, regardless of the subject population, study design or intervention used [20].
Caution
If you are concerned about your vitamin C intake, talk to your doctor to determine whether supplements could be right for you.
It is important to note that reactive oxygen species may actually control beneficial training adaptations that high doses of Vitamin C prevent from occurring [46, 47].
Supplemental intakes greater than 500 mg per day may cause kidney stones in those that are prone to them [1].
Vitamin C can enhance iron absorption by maintaining iron in ferrous (Fe2+) rather than ferric (Fe3+) state. This is beneficial in some patients (such as those with gut issues and low ferritin) but not in those that suffer from medical conditions that cause iron overload [1].
High intake of Vitamin C exerts a pro-oxidant effect by its interaction with metal ions via a number of established RONS generating systems. Caution should be exerted regarding surplus vitamin C intake for patients with chronic inflammatory diseases or atherosclerosis [71, 5].
Some research has found that combining high-dose Vitamin C and vitamin E supplementation can be harmful, even though the harm may be restricted to selected groups among smokers [72].
Vitamin C intake might be responsible for high serum uric acid levels, based on a study in Korean rural communities [73].
Higher uric acid can be a good thing, such as improving productivity and intelligence, but it can cause problems if you’re prone to kidney stones or gout.
High Vitamin C intake from supplements was associated with an increased risk of cardiovascular disease mortality in postmenopausal women with diabetes [74].
Takeaway
Vitamin C is an essential nutrient, meaning that we need to get sufficient amounts from diet to be healthy and prevent deficiency. Since vitamin C is water-soluble, it isn’t stored in large amounts in the body.
Getting adequate amounts of vitamin C supports brain, bone, skin, and lung health. Dietary vitamin C also boosts the bioavailability of vitamin E and plant-based iron.
There are countless purported benefits of vitamin C supplementation, but only some are supported by decent evidence. Supplementation is effective for scurvy, a severe form of vitamin C deficiency. Supplements may also help prevent age-related macular degeneration and the common cold.
The upper tolerable intake is 2 g/day; taking more is considered unsafe. The RDA is 75 mg for women and 90 mg for men, while most supplements contain 100-500 mg of vitamin C.
