Ask Doctor K: A cure for the common cold is not coming soon

DEAR DOCTOR K: Is there any way to prevent a cold?

DEAR READER: Now, there’s a short, simple question. If only I had a short, simple answer.

Colds are caused by viruses – more than 200 different types. Because the infection is not caused by bacteria, antibiotics don’t help. Over-the-counter cold medicines are available, but not always effective.

So the search continues for anything that can fend off cold-causing viruses or speed their exit from your body. Here is a rundown of some of the candidates:

VITAMINS. Biochemist Linus Pauling proposed that large daily doses of vitamin C – 1,000 to 2,000 milligrams – could prevent colds. Pauling was a genius who made major scientific discoveries and was awarded the Nobel Prize. But even geniuses can be wrong. By and large, research hasn’t supported his assertion. One study did report a benefit, but just in people who engage in extreme exercise.

There’s some evidence that vitamins D and E might help fend off respiratory infections, but the evidence is weak. I don’t recommend either vitamin for cold-fighting purposes.

ECHINACEA. The research hasn’t been very encouraging. One review found some evidence that a certain part of one particular species of the Echinacea plant family might be an effective early treatment for colds in adults. Not exactly a ringing endorsement.

Other plant-based treatments, such as ginseng, elderberry, garlic and olive leaf, have been offered as cold preventives and cures. But none has emerged as clearly effective.

ZINC. The results have been mixed. Two studies in children found that zinc might reduce the number of colds. The evidence in adults is unclear and hotly debated. Taking too much zinc can damage smell and taste. For now, I wouldn’t recommend zinc.

EXERCISE. Here’s another reason to work out. Regular moderate exercise seems to invigorate the immune system. While there are abundant health benefits from regular exercise, I’d say the evidence that exercise reduces the number of colds is pretty weak.

SLEEP. Your mother was right: Getting a good night’s sleep keeps you healthy and may keep colds away. In one study, people who got less than seven hours of sleep a night were almost three times as likely to get a cold as those who got eight or more hours of sleep.

PROBIOTICS. A study in 2015 reported that specific probiotics (lactobacillus and Bifidobacterium) reduced the number of respiratory infections (not just the common cold) and the length of time people were sick. However, the quality of the study was not very good.

I know I’m going to get letters from people who swear that a vitamin, or an herbal preparation, or zinc works for them. I’m not really disagreeing with them.

Studies ask whether a particular treatment works for the average person. A treatment that does not work for the average person still may work for some people; perhaps they have different genes. If you’re convinced a treatment helps you, and if it doesn’t pose any risk (and most of those above don’t), then why not use it?

(This column is an update of one that ran originally in March 2013.)

Dr. Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.