When afflicted with the common cold, many people chug orange juice and swallow vitamin C supplements in an attempt to "boost" their immune systems. But vitamin C supplements don't ward off the common cold in most people, and there's even less evidence that they grant immunity against SARS-CoV-2, the virus that causes COVID-19.
The myth, the legend
Vitamin C, also known as ascorbic acid,
became known as an immune-boosting supernutrient after two-time Nobel Prize
winner Linus Pauling touted the substance's supposed benefits in a series of
books, Live Science previously reported. Pauling claimed that taking large
doses of vitamin C could not only prevent the common cold, but also help thwart
more severe illnesses like cancer and heart disease.
Since Pauling published his books, in the
1970s, his bolder claims have not stood up to scientific scrutiny. However,
recent research does suggest that vitamin C supplements reduce the duration of
colds in the general population, according to a 2013 review of several dozen
studies.
The review found that vitamin C supplements
taken during a cold can reduce the duration of the illness by 8% in adults and
14% in children. Practically, that means that supplementing vitamin C can
shorten the duration of a cold by about one day. Participants in each study
supplemented vitamin C for varying periods, but generally, the daily dose was
at least 200 milligrams.
Several of the reviewed studies included
people under intense physical stress, including marathon runners and soldiers
training in the Arctic. Among these individuals, those who took vitamin C were
about half as likely to catch a cold as those who did not take such
supplements. But in the general population, the supplements did not prevent the
common cold.
Likewise, no evidence suggests that vitamin
C supplements can help prevent COVID-19, Dr. William Schaffner, a professor of
preventive medicine and infectious diseases at Vanderbilt University Medical
Center in Tennessee, told New York Times Parenting.
"If there's going to be an advantage,
it's going to be very modest," Schaffner said.
Some scientists are testing if vitamin C
could alleviate symptoms and improve outcomes for patients with COVID-19 — if
given in a high enough dose. Researchers at Zhongnan Hospital of Wuhan
University launched a clinical trial with 140 patients in February to test
whether ultrahigh doses of vitamin C, delivered intravenously, could treat the
viral infection more effectively than a placebo. The test group will receive
infusions twice a day for seven days, with each infusion containing 12g of
vitamin C. (The daily recommendation for an adult man is only 90mg.)
The trial will be completed in September,
and no results are yet available, according to ClinicalTrials.gov. In the
meantime, Chinese scientists have launched dozens of other clinical trials as
well, testing everything from antivirals to antibody therapies to traditional
Chinese medicines.
Beyond the common cold
Although supplements can't ward off the
common cold, vitamin C is still important to your health. It serves essential
roles in the human body and supports normal immune function, according to a
2017 report in the journal Nutrients.
Vitamin C acts as an antioxidant, meaning
it neutralizes free radicals generated by the body's normal metabolism and by
exposure to environmental stressors, including ultraviolet radiation and air
pollution. Free radicals are charged particles that can damage cells, tissues
and genetic material if left unchecked, and thus trigger harmful inflammation.
Besides stopping free radicals, vitamin C
helps to activate several key enzymes in the body, which go on to synthesize
hormones and build collagen, a tough protein found in skin and connective
tissues, according to the 2017 report. These hormones help control the response
of the cardiovascular system to severe infections, while collagen fortifies the
skin against injury.
Vitamin C may also bolster the fatty
membranes in skin and connective tissue, thus protecting organs like the lungs
from pathogens, according to cell culture and preclinical studies. When bugs do
infiltrate the body, vitamin C helps direct immune cells called neutrophils to
the site of infection and defends these cells against free radicals, the 2017
report noted.
In short, the body relies on vitamin C to
launch an effective immune response while sustaining minimal damage. However,
the body can't make its own vitamin C or store the nutrient efficiently, as the
water-soluble vitamin dissolves once ingested and is excreted in the urine, according
to the National Institutes of Health (NIH). The best way to meet your daily
requirement is to consume vitamin-rich fruits, vegetables and fortified foods.
The recommended dose depends on your age,
sex, pregnancy and breastfeeding status, but in general, adult men are
recommended to ingest at least 90 milligrams (mg) a day, and adult women should
consume at least 75 mg. People who smoke should add 35 mg to their recommended
dose, as smoking depletes the body of available vitamin C, according to the NIH.
Note that high doses of vitamin C,
exceeding a daily level of 2,000 mg, can cause nausea, diarrhea and abdominal
pain in many people, Live Science previously reported. Additionally, men who
have had kidney stones in the past and who test high for a chemical called
oxalate should avoid supplementing with vitamin C, as the substance may enhance
the formation of those types of stones, Stephen Lawson, a researcher at the
Linus Pauling Institute at Oregon State University, told Live Science at that
time. (The Linus Pauling Institute was originally co-founded by Pauling himself
to conduct research on nutrition and its role in health and disease.)
"Be wary of hype and
headlines"
While vitamin C supplements pose little
risk to consumers, other so-called "immune-boosting" products could
be harmful.
Since the COVID-19 outbreak began in the
United States, the U.S. Food and Drug Administration (FDA) and the Federal
Trade Commission (FTC) have already issued warning letters to seven
companies for selling fraudulent products that promise to cure, treat or
prevent the viral infection. "These warning letters are just the first
step," FTC Chairman Joe Simons said in a news release. "We're
prepared to take enforcement actions against companies that continue to market
this type of scam."
Note that no evidence suggests that other
so-called immune-boosting supplements — such as zinc, green tea or echinacea —
help to prevent SARS-CoV-2 infections, Dr. Mark Mulligan, division director of
the infectious diseases and vaccine center at NYU Langone Medical Center, told
New York Times Parenting. "I do not recommend spending money on
supplements for this purpose," Mulligan said.
"The medical profession still doesn't
know exactly how to influence the immune system, despite what supplement
products may claim," Julie Stefanski, a registered dietitian nutritionist
and spokeswoman for the Academy of Nutrition & Dietetics, told The
Washington Post.
The FDA does not vet dietary
supplements as it does pharmaceutical medications; that means that
supplement manufacturers can place new products on the market without first
proving that the substances are either safe or effective. The FDA and FTC step
in after the fact to police a product that presents "a significant or
unreasonable risk of illness or injury or that is otherwise adulterated or
misbranded."
These agencies rely heavily on reports from
consumers, health care professionals and supplement manufacturers themselves to
identify sketchy products and pull them off the market. That said, the FDA
encourages consumers to stay informed and "be wary of hype and
headlines," saying that unsubstantiated claims crop up on supplement
labels all the time and it's often up to you to spot them.
When in doubt, the FDA recommends that you
"let your health care professional advise you on sorting reliable
information from questionable information." Thankfully, in the case of
vitamin C, supplements don't typically cause harmful side effects, unless
consumed in excess.

Source: Live Science