The Latest Research on Vitamin C
By Deanna Minich
Vitamin C is no stranger to the spotlight when it comes to powerful nutrients.
When you get a cold, you might turn to vitamin C to give your immune system
a boost, or you might supplement with it to help combat oxidative stress.
Many of vitamin C’s functions are well studied and can be found in any
nutritional textbook and articles out in the blogosphere.
As a quick recap, here are some of vitamin C‘s most recognized roles in the body:
– Immune system support
– Collagen synthesis
– L-carnitine synthesis
– Neurotransmitter synthesis
– Antioxidant that also regenerates other antioxidants, specifically vitamin E
– Increases non-heme (plant based) iron absorption
Scurvy, common among sailors in the 15th and 16th centuries, is a disease that arises when there is a deficiency of vitamin C. The early symptoms include fatigue, lethargy, and malaise. As it progresses, it causes anemia, bone pain, easy bruising, swelling, poor wound healing, mood changes, depression, and other symptoms. It can become very serious and even lead to death if not treated.
Although a true deficiency might be rare today, having insufficient levels also leads to poor health. Our knowledge regarding the important actions and roles that vitamin C has in the body—and why it is important to have sufficient quantities—continually expands. So, let’s take a look at what’s new with vitamin C with a quick research roundup of some of the more recent studies in the literature.
Neurodegeneration and Alzheimer’s Disease
Recent studies on vitamin C’s potential to help prevent and perhaps even alleviate Alzheimer’s Disease and other disorders caused by neurodegeneration found:
A reduced risk of developing cognitive decline. Using data from a cohort study, researchers reviewed the impact of taking vitamin E and C supplements on cognitive decline. Supplementing with vitamin C and E resulted in roughly three-quarters the risk of developing cognitive impairment, not dementia, and there was just under two-thirds the risk of developing Alzheimer’s disease and all-cause dementia. For those who appreciate the science, the adjusted hazard ratio was 0.77 for cognitive impairment, not dementia; 0.60 for Alzheimer’s disease; and 0.62 for all-cause dementia, all of which were significant and remained so in fully adjusted models other than cognitive impairment, not dementia.
In another study, lower plasma levels of vitamin C correlated with a higher risk of increased carotid intima-media thickness (IMT). Increased IMT has been shown to increase the risk of cardiovascular disease and cognitive impairment. This points to a potentially protective effect of vitamin C against Alzheimer’s disease and similar vascular and cognitive aging.
Based on these two studies, it appears as though having sufficient vitamin C plays a key role in protecting the brain. This makes it especially important for you to consume plenty of vitamin-C rich foods as you age.
Several studies have come out in the past decade or so looking at the association between vitamin C and heart health. Below are highlights of a couple recent studies:
A meta-analysis found vitamin C treatment after cardiac surgery was safe and potentially effective in reducing the incidence of postoperative atrial fibrillation. This is the most common surgical complication, and it can lead to twice the incidence of heart failure and stroke. Finding ways to prevent postoperative atrial fibrillation could contribute to better surgical outcomes and reduced mortality.
Patients with metabolic syndrome have lower plasma levels of vitamin C, as well as the other key antioxidant vitamins (vitamins A and E). Low levels were not associated with their dietary intake, but weight did play a role. Those who had a higher BMI also had a lower level of vitamin C, pointing to antioxidant deficiency or impairment. Therefore, regardless of the diet, those who were overweight or obese still had lower levels of vitamin C in their blood, most likely due to increased antioxidant needs. Therefore, it is even more important for those with a higher BMI to focus on consuming sufficient antioxidants, especially vitamin C, through their diet and possibly supplementation.
A healthy diet, especially one rich in vegetables and fruit, is an important component of heart health. One reason might be that the vitamin C in plant foods helps ensure you have a large enough antioxidant capacity when you are stressed, whether from a surgery or excess body fat.
We already know that supporting the immune system is an important task of vitamin C. New research provides even more evidence, as shown below:
One randomized, controlled pilot study found that taking probiotics with 50 mg of vitamin C reduced the incidence rate of upper respiratory tract infections in preschool children compared to the placebo group. There was also a reduction in the days absent from school and the number of days for which medication was needed compared to the placebo group.
In a randomized control trial, vitamin C supplementation (500 mg) was found to help men with below adequate or deficient vitamin C status at the beginning of the study overcome a cold faster. After taking vitamin C, the duration of infection with the common cold was reduced 59 percent compared to the control group. The vitamin C group also experienced a modest increase in the physical activity score and increased fasting serum vitamin C levels.
Other Promising Findings
There are many other studies pointing to possible benefits from this antioxidant vitamin. Some interesting and promising findings include:
A recent study analyzed data from 3,283 adults in the Korea 2012 National Health and Nutrition Examination Survey. Low intakes of vitamin C, as well as other nutrients, had a significant association with COPD (chronic obstructive pulmonary disease). Low vitamin C intake was one of four elements that had a significant independent risk factor; the other four were being male, older, and a smoker. The study found that higher vitamin C intake is protective, independent of smoking.
In patients with hypothyroidism and gastritis (which contributes to malabsorption of thyroid medication), taking vitamin C helped improve absorption of levothyroxine, which in turn improved their serum TSH, free T4, and T3 levels. These are the thyroid hormones that play an important role in regulating metabolism, growth and development, and neural differentiation.
A cohort study found that high levels (over 30 grams) of intravenous vitamin C over a treatment period that lasted 90 minutes reduced blood pressure 6 to 7 mmHg and 8 to 9 mmHg in prehypertensive patients.
A cross-sectional study looking at middle-aged and older adults found an inverse association between vitamin C intake (adjusted for energy intake) and risk for developing non-alcoholic fatty liver disease.
These studies point to the importance of ensuring you have an adequate supply at all times for your general health and well being. As an added bonus, you protect yourself from an early death. A report reviewing two cohort studies found an inverse association between vitamin C intake and all-cause and cardiovascular disease mortality in adults in China.
How to Get Sufficient Vitamin C
It is easy to boost your vitamin C intake: just add some fruits and vegetables to your diet, especially if you fall short of the recommended 9 to 14 servings. In a study combining four randomized-controlled trials conducted under similar guidelines by the same research team, there was a 24 percent increase in vitamin C intake per one additional portion of fruit and vegetable added to the diet, which was statistically significant. For a targeted increase, try some of the following foods, which are rich in vitamin C and listed in descending order:
– Acerola cherries
– Orange juice
– Red, green, and yellow peppers
– Mustard spinach
– Tomato juice
– Sun dried tomatoes
One thing this list has in common is that they are colorful foods! Make a point to eat a colorful diet made up of every color of the rainbow. This ensures you provide your body with a wide variety of nutrients, including vitamin C.
If you struggle to consume enough vitamin-C rich foods, you might wish to turn to supplements. There are a few things you need to know¹:
Most supplements use ascorbic acid, which has a similar bioavailability to what you find in food.
The body starts to absorb less vitamin C once you go above doses of 1,250 mg. That is why for maximum absorption, it is generally recommended to split high doses to two or three throughout the day.
The most common side effect is diarrhea, and you might also experience abdominal pain. Typically, these symptoms are dose related. This means they are more likely to occur the higher the dose. This is another reason to split high doses.
Vitamin C increases the absorption of non-heme iron, which is the iron found in plants such as lentils, soy, quinoa and leafy greens. Therefore, if you are at risk of an iron overload, do not take vitamin C when you consume these foods. Conversely, if you are iron deficient, increase your non-heme iron absorption through consuming vitamin C rich foods and/or supplements.
As with any supplement, discuss potential medication interactions and other risk factors with your doctor or pharmacist before taking the supplement.
Make sure to have bioflavonoids included in your vitamin C supplement for a complete complement of vitamin C activity.
When you choose a supplement, you want to make sure that it is high quality. One of the best ways to do that is to look for those certified by a third-party, such as Consumer Labs, the Natural Products Association, NSF International, and US Pharmacopeia. Always review the active and inactive ingredients so that you know what is in the supplement. Be wary of “proprietary” blends that do not detail the ingredients. Other ingredients to avoid include wheat, gluten, lactose, hydrogenated oils, sweeteners, artificial colors, and anything else you generally would not wish to ingest.
There will always be more research looking into additional benefits of consuming vitamin C, and there’s no time like the present to focus on your intake so that you benefit from all that vitamin C does to the body, both the actions currently known and those that will only be revealed in the future. Always check with your healthcare practitioner on whether you need more vitamin C from your diet or from a supplement.
Gaby, A.R. (2011). Chapter 22:Vitamin C.In Nutritional Medicine (1st ed.) [eBook version]. Concord, NH: Fritz Perlberg Publishing. Available from https://doctorgaby.com/the-book/.