Should I Take Tons of Mega-Dose Vitamin C Packets When I Have a Cold?

Hello again, internet friends! I am back in the JC/NYC area after yet another whirlwind mini trip around the US last week. Phew. While I was gone I actually wrote a whole post on Eating Disorders in honor of National Eating Disorders Awareness week and scheduled it to post, but it failed, and now I feel like it’s beyond #NEDA week and I feel weird publishing it. Would you be interested anyway? Let me know down below.

Anywho, while I was at the Charlotte airport, I was watching some ladies slam Emergen-C packets one after another and posted a selfie to my Instagram story with the caption “People know Emergen-C doesn’t work, right?”

And the response I got was overwhelming. A lot of people seemed to not only surprised to hear this information, but wanted to know exactly how or why I don’t recommend mega-dose supplements such as Emergen-C or Arbornne to cure the common cold.

I thought I’d go a little further into the topic here, #ontheblog, and I hope to film a little “Nutrition FAQs” video about it too next week, once I’m back in Wisconsin and have the time and space to film.

Anyways, let’s get to chatting about Emergen-C and the common cold. Starting with the basics…

How Much Vitamin C Do You Actually Need?


Well, according to the USDA dietary guidelines for Americans, the average healthy adult women needs 75mg, and the average healthy adult male needs 90mg. Smokers need an additional 35 mg per day, as some of vitamin is used to quench free-radicals and combat oxidative stress from toxins exhaled from cigarette smoke.

Pregnant and lactating women need more, requiring roughly 85mg/day and 120 mg/day respectively.

Vitamin C is naturally found in high levels in many foods, including strawberries (~90mg/cup), bell peppers (~120 mg/cup), guavas (~126 mg/fruit), kale (~80mg/cup) oranges (~70mg/fruit), and kiwis (~80mg/fruit). Most people in developed countries do not suffer from vitamin C deficiency. Select groups, including smokers and low-income populations, may be at an increased risk of deficiency.

Each packet of Emergen-C contains 1,000 mg of vitamin C. As you can see, this is much, much more than an adult or child needs; in fact, you could say it’s over 1000% of the RDA.

So, Does Emergen-C Work?


First, let’s get one thing clear: there are exactly zero scientific studies that have specifically tested the product Emergen-C and its potential impact on incidence (number of people who get a cold) or duration (length) of a cold.

Emergen-C, like all dietary supplements, is not subject to regulation for purity, safety, nor efficacy, and thus, did not require any testing before hitting the market (though they did settle a lawsuit in 2014 for making false/unproven claims about their product).

In addition to being untested or unregulated, there is no guarantee that Emergen-C packets contain what is listed on the box. A worrisome aspect of the supplement industry is that dietary supplements can really contain anything (sugar, toxic impurities, etc) and be sold on a massive scale. This is a problem not just with cold supplements, but with all supplements, and is something to keep in mind next time a health influencer suggests you spend $50 on a moon potion.

Anyways, let’s turn back to Emergen-C and the common cold. One of the main advertised selling points of Emergen-C, and one of the main reasons people seek it out, is for it’s high vitamin C content. Many people seem to think mega-doses of vitamin C are a magic-bullet to cure the common cold. Which begs the question…

Can Vitamin C Prevent My Cold?


There actually isn’t much substantial evidence to suggest large doses of vitamin C has any significant effect to prevent or cure the common cold. The idea was first proposed by an influential chemist, Linus Pauling, in the 1970s, and results of studies since then have been controversial and inconsistent.

A 2007 Cochrane review of existing placebo-controlled trials found that use of vitamin C did not significantly reduce the risk of developing a cold in the general population. Vitamin C supplementation also failed to reduce the length of cold duration or symptom severity. The review did report that vitamin C did slightly reduce the duration of colds in select groups of extreme athletes by 1 day, which is compelling, but an area I believe warrants further research.

And a 2013 Cochrane review of placebo-controlled trials that tested vitamin C supplements and common cold outcomes also concluded that vitamin C supplementation to reduce the incidence of the common cold in the general population is not justified, but may have limited benefits to select groups of people undergoing extreme periods of severe exercise. The relationship found was simply a correlation, and causation was not proven.

It also concluded that although some supplementation trials have shown vitamin C may reduce the duration of colds, this has not been replicated in the few therapeutic rails that have been carried out, and that further research is warranted.

Importantly, studies that showed any slight decrease in cold duration (ie, 1 day) did not find decreases in cold duration in subjects who started taking vitamin C after the onset of a cold, only in those who were taking it before symptoms started compared to those not taking it before their colds started. Most people who take Emergen-C do so when they start to feel a cold coming on, which according to these epi studies, would have no effect on symptom duration or severity.

It’s also important to note that most of these studies looked at doses of 200-250 mg Vitamin C (which is not the dose found in Emergen-C), and none of them specifically tested any of the cold prevention supplements on the market. Thus, it’s difficult to make statements about definitive claims about cold supplements, especially since all those products, as mentioned above, have a total lack of evidence.

At present, I would say there isn’t enough strong evidence that I would feel comfortable suggesting the use of mega-doses of vitamin C to prevent or treat a common cold to the general population, especially when you weigh potential risks against the lack of evidence for benefits. Sure, there is a small amount of data to suggest it may help select groups to reduce cold duration by a day or so, but for most of the population, I don’t believe there is enough evidence that I would comfortably recommend spending your money on the stuff.

Risks of Consuming Too Much Vitamin C:

What do I mean by potential risks? Well, as mentioned above, Emergen-C doesn’t just have 100% RDA vitamin C; it has over 1000%.

When I mentioned the whole Emergen-C thing on Instagram, another thing a lot of people seemed surprised to learn was that it is, in fact possible to over-consume vitamin C. Yes, it’s true: when it comes to vitamins, more is not always better. Most follow a U-Shaped curve; if you have too much or little, you you may experience adverse health impacts. I used a banana to visualize this concept on my Instagram stories, and included the visual below:


First, vitamin C is a water soluble vitamin; once your body gets ‘enough’ (ie, the amount it can absorb and process at a time, which for vitamin C, is believed to be about 30-180mg/day), the rest does not provide an additional benefit and is excreted in your urine.

But as with many things, the dose makes the poison, and it is possible to overdo it. The upper tolerable level of vitamin C is 2,000 mg/day. One packet of Emergen-C contains 1,000 mg. So if you’re like the ladies I saw at the airport and slam several in a row, or take multiple doses per day for extended periods of time, you may be exposing yourself to a potentially adverse dose of vitamin C.

Although vitamin C has a relatively low toxicity, too much of the stuff can cause diarrhea, abdominal cramps, GI disturbances including gas and bloating, and increased risks of kidney stones (especially in those with kidney disease).

There are also some concerns that high levels of vitamin C may act as a pro-oxidant (fueling oxidative damage), and/or that it may reduce vitamin B12 and copper levels in the body, although these findings were in vitro, are in need of further investigation, and generally thought to be relatively unconcerning for the general healthy population.

What Can I Do to Prevent a Common Cold?


Although there is no data to support claims made by cold-curing supplements such as Emergen-C to prevent and cure the common cold, nor is there significant data to suggest taking vitamin C will prevent a cold, I would still advise that consuming a healthy robust and nutrient-rich diet to support your overall health and well-being, not only during cold and flu season, but year round.

If you are suffering from micronutrient deficiencies, you may be more susceptible to certain illnesses, so making sure you are getting a wide variety of micronutrient-dense foods (like fruits and vegetables, nuts and seeds, fortified plant or other milk products, and fortified cereals) is wise and encouraged. And when possible, consuming the nutrients from food over supplements, is advised.

Besides a healthful diet, simple things like hand washing and good hygiene, as well as getting adequate sleep on a regular basis, are helpful in preventing the spread or contraction of certain illnesses.

So what to do when you feel a cold coming on? Rather than spend oodles of money on unproven supplement packets, powders, and pills, I suggest rest, a healthful diet, ample fluids, self-care, and some solid hand-washing and good hygiene.

Rest up, eat up, and be well!



If you’ve made it this far, I just wanted to say thank you for reading! You may also like the following semi-related content:

Got a nutrition question? Drop it below in the comments, or hit me up on InstagramTwitter, or YouTube.

As I move forward and shift my primary academic focus back to nutrition (while always keeping environmental health tucked in my back pocket!) I am so pumped and motivated to share the education and experiences to help people demystify nutrition and climate and health! I am planning to get back to film more videos over and after spring break (once I’m no longer hosting my mom at my studio as I have been the past 7 weeks) and I welcome blog post and video topic suggestions.

Thank you again for your time and support; you mean the world to me (and Millie too)! Be well! *internet hugs*

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