Read an Excerpt from Does Coffee Cause Cancer?

MYTH #1

Vitamin C Fights the Common Cold

I don’t like to fly. I don’t like the food, being packed into my seat like a sardine, or the minimalist bathroom that is often a few shades off my ideal for cleanliness after the first hour of the flight.  The trick, I eventually learned, was to medicate myself about 30 minutes before takeoff. Gravol not only quells my airsickness, it also knocks me out and lets me sleep through most of the flight.

So there I was in the airport lounge, doing some quick math in my head, trying to figure out the ideal time to take my pill, when the man next to me tapped me on the shoulder and asked me a question. Years later, I wondered what would have happened if he had gone up to someone else, how that weekend might have played out differently as a result. But by fate or luck, he came up to me.

“Is that cold medicine, by any chance?” he asked.

He didn’t inspire confidence. His hair was messy, and he was flushed with a light tinge of sweat, possibly from a mild fever. His nose had a reddish glow, which suggested either chronic alcoholism or a recent cold. I gave him the benefit of the doubt and assumed the latter. When he sneezed, I had my answer.

“Do you have any cold medicine?” he asked.

I unzipped the front pouch of my carry-on, fished out a small bottle of acetaminophen, and shook two tablets into his outstretched palm. He popped the tablets in his mouth and swallowed them without water, not even looking at the pills. I could have poisoned him and committed the perfect crime. I shook off the thought. I’d been reading too much Agatha Christie and P.D. James.

“You’re a life saver.” He held out his hand and told me his name was Jim.

I looked at his outstretched hand, the hand he’d just sneezed into. I didn’t want to be rude, but I didn’t want to shake it. “You shouldn’t take pills from strangers.”

Jim’s face froze.

“I mean that was just generic acetaminophen, but . ..”

“Acetamino . . . ?” he stumbled.

I told him acetaminophen was just the chemical name for Tylenol. When I told him I was a doctor, he relaxed a little. He obviously assumed that the Hippocratic oath offered some protection against random airport poisonings, which to some degree it probably did. “I need some vitamin C,” he said. “I don’t know if I’m really sick, but I figure I should treat it and be safe.”

The voice in my head said, “Don’t engage! Don’t engage! This is a natural breakpoint for the conversation.” It was good advice. But I don’t always listen to that voice in my head, even if it does sound like Michael Caine and carries all the implied authority of a British accent. It’s hard for me to let stuff like this go.

“You know, vitamin C doesn’t really help fight off the common cold.”

“Yes, it does. People use it all the time.”

“I didn’t say people don’t use it. I said it doesn’t work.”

“Haven’t people tested vitamin C as a cold treatment?” he asked.

“They have. I think there have been over 30 studies with maybe over ten thousand people in them.”

“So what’s the problem? Either vitamin C works or it doesn’t.”

The display above the boarding gate said we wouldn’t board for at least 40 minutes. Maybe longer. Outside the gate, our plane hadn’t even arrived. We might be here for a while. I figured I would try at an explanation. “You’ve probably heard that if you take vitamin C when you get a cold, the cold goes away faster.”

“Of course, that’s why I take it.”

“Here’s the thing though. Taking vitamin C when you get sick doesn’t treat a cold.”

“Does too. There was a study on this . . . I think,” he said.

“Actually, there’ve been seven studies on this question, specifically, on whether vitamin C makes a cold go away faster.”

“Even better!”

“They were negative.”

Jim frowned. Nobody likes having their worldview shaken, even on relatively trivial issues like the medical benefits of vitamins. But when you review the scientific evidence on the subject, there’s no benefit to taking vitamin C when you start to get sick. All of the research was done on people who take vitamin C regularly.

Jim looked unhappy. “I mean it’s one thing to take it when you get sick, but every day of your life just to prevent a cold?”

“It doesn’t prevent colds.”

“But you just said…”

“There was only one group of people where that did happen.”

“Ah good. Who?” He seemed pleased. Completely abandoning something you believe in is hard for people to do.

“Marathon runners, skiers, and Canadian soldiers performing subarctic military maneuvers.”

“Marathon runners, skiers, and…what?”

I had to repeat myself.

“Canada has its own army?” he asked. “Oh, right, the Mounties.”

“No, that’s . . . It doesn’t matter. The point is —”

“So there are situations where vitamin C works?”

He’d regained some of his enthusiasm for the medical benefits of what I assumed was his favorite vitamin. “Are you a marathon runner, skier, or a Canadian soldier?” I asked.

He looked down at the slight belly peeking over his belt. He wasn’t in bad shape, but he probably wasn’t an elite athlete either. “No, I’m not good with the cold,” he said.  “What does that mean for me as a non-runner-skier-soldier?”

“That’s tricky. Some people think vitamin C works in these groups because it helps people who are exposed to periods of brief physical stress.”

Jim thought that made sense. But I had to burst his bubble. I told him this could all be due to random chance.

Most people don’t love talking about statistics as much as I do, and why would they, but random chance is a serious problem in medical research. I sat down and explained to Jim why sometimes looking at sub-groups of people in medical research can lead you astray. We had a long conversation about sub-group analysis, multiple hypothesis testing, and why over-analyzing your data can lead to spurious results. It’s why you can analyze data and show that your zodiac sign can blunt the medical benefits of aspirin during a heart attack. Or that the divorce rate in Maine is linked to per capital margarine consumption. Or that the number of people who drown by falling into a pool is correlated with the number of films per year Nicolas Cage has appeared in. That’s when I found out that Jim really likes Nicolas Cage. So while, it might seem like vitamin C prevents colds, a lot of it is probably random statistical noise.

It was a long talk. Only as we eventually boarded our flight did I realize I had forgotten to take my pill. I cursed Jim for coming up to me of all people and distracting me. But I knew it wasn’t his fault. Some things in life are just random.

* * *

Dr. Christopher Labos is a cardiologist and has a master’s degree in epidemiology. He is a regular contributor to the Montreal Gazette, CJAD radio, CTV Montreal, and CBC’s Morning Live. He also blogs for Medscape and co-hosts a podcast, The Body of Evidence. He lives in Montreal, QC.