by Emily Finnan
Cold season has hit. Some of you may have already experienced the hallmark signs: unrelenting cough, non-stop dripping nose, and eyes so watery from sneezing, you can barely see. Unfortunately, even though in America one billion common cold infections occur yearly, there is no cure. Nothing can make your cold go away.
To fill the void left by pharmaceuticals, which can’t treat this prevalent condition, herbal and dietary supplements seem to step in. Vitamin C supplements are one popular remedy for colds. One brand, Emergen-C, which sales peak in the winter months, sells over 500 million supplement packets yearly. The tangy powder can be mixed into a glass of water for a fizzy, fruity drink that, in one packet, provides 1,667% of the daily value of vitamin C, 500% of the daily value of vitamin B6, and 417% of the daily value of vitamin B12, among 12 additional vitamins and minerals. You can see the supplement facts for the full information.
There has been a substantial amount of research on vitamin C and colds. So what does the evidence say? Is vitamin C just a tasty placebo?
Vitamin C & Immunity
Vitamin C has a true role in immunity. When white blood cells attack invader pathogens, like a cold virus, they release damaging substances to kill it. But in the process, the cells can damage themselves. This is where antioxidants like vitamin C, with the help of vitamin E, come in. They protect white blood cells via their antioxidant function.
In fact, the Recommended Daily Allowance, or RDA, is based on immune function. It is the amount of vitamin C needed to maintain maximum neutrophil levels (a type of white blood cell) with minimal urinary excretion. This is 90 mg a day for men and 75 mg a day for women.
Most supplements provide 1,000 mg of vitamin C. That’s 11 times the RDA. Logically, if vitamin C helps immune cells, the more the better. Is this is the “immune boosting” the supplements often speak of?
Immune boosting is a vague, perhaps intentionally, term. It has no scientific meaning. “You can have a hyperactive immune system, but that wouldn’t be good. You want to be able to fight the cold but then you need to have your immune system slow back down when you’re no longer sick,” says Dr. Jeffrey Blumberg, director of the Antioxidants Research Laboratory at the USDA Human Nutrition Research Center on Aging. A supplement can’t turn a healthy immune system into a “better, “boosted” system.
But taking a 1,000 mg supplement appears to have no harm. . As Dr. Blumberg says, “high doses, theoretically, of any nutrient can kill you. However, I’m unaware of any long-term untoward consequences of vitamin C, at any dose.” Some people have taken up to 30,000 mg per day without reports of adverse side effects! Any excess absorbed vitamin C is quickly excreted in the urine.
There is a tolerable upper limit set for vitamin C: 2,000 mg per day. This is because doses of this level, and higher, can cause GI upset due to our body’s limited ability to absorb large doses. At intakes greater than 1,000 mg, absorption falls to less than 50%. If unabsorbed vitamin C makes it to the colon, this hyperosmotic load can lead to things like diarrhea. As Dr. Blumberg says, “This minor side effect has its own automatic safety switch. Someone says, ‘Gee this gives me diarrhea. I think I’ll take less.’ ”
Vitamin C & Colds
The popular theory that vitamin C can alleviate or prevent the common cold stems from chemist Dr. Linus Pauling, an esteemed double Nobel Prize winner. In 1970 he wrote a book titled Vitamin C and the Common Cold. In this book he claimed that 1,000 mg of vitamin C could reduce your risk of catching a cold by 45%. This claim was largely based on one study of children at a skiing camp in the Swiss Alps.
Over 40 years later, and 67 randomize placebo-controlled trials later, we’ve learned a lot.
A 2013 systematic review of vitamin C and colds pooled over 11,000 participants who took between 200 and 2,000 mg of vitamin C daily for 2 weeks to 5 years. Vitamin C supplements had no effect on prevention or severity of colds. Among the vitamin C intervention group, they did find a slight decrease in duration of colds. Adults had 8% shorter colds. For people who were currently undergoing short-term, intense physical activity the vitamin C intervention group was 50% less likely to get a cold. These participants were marathon runners, skiers, and soldiers working in the subarctic. Perhaps that’s why Dr. Paul’s skiing children benefited from vitamin C?
In the other group of studies participants were given between 1,500 and 8,000 mg of vitamin C on the first day of cold symptoms. After pooling over 3,000 cold events, vitamin C was found to have no significant effect on duration or severity of cold symptoms.
To Take or Not to Take
Is vitamin C going to cure your cold? No. And neither will anything else. Research has shown that unless you’re undergoing some intense exercise, vitamin C only has an effect of slightly shorter colds, if taken daily. The authors of the review state, “This level of benefit does not justify long-term supplementation in its own right. So far, therapeutic supplementation has not been shown to be effective.”
Vitamin C is essential to immunity, so it is important to obtain an adequate amount in your diet or through supplements. On average, Americans consume vitamin C in amounts above the RDA. However, about 30% of Americans’ intakes are inadequate, falling below the Estimated Average Requirement.
You can obtain adequate vitamin C from diet alone. “People who eat a lot of citrus fruits and leafy greens could be eating up to 500 mg of vitamin C. Following the Dietary Guidelines for Americans will put you well over the RDA,” says Dr. Blumberg.
For those who are concerned about meeting vitamin C needs through diet, or choose to supplement, dividing your vitamin C supplement into smaller, more frequent doses would allow for more absorption rather than a one-time large dose.
Whether you prefer a vitamin C supplement or a fruit salad, my advice is the same –good luck this cold season!
Emily Finnan is a registered dietitian and a 2nd year biochemical and molecular nutrition masters student. You can read her nutrition quips and MBTA complaints on twitter @emilyyfin.