And hopefully, you're already doing it.

By Samantha Zabell
Updated September 01, 2015
We already know that cold weather doesn’t directly cause colds, but many of us are more likely to catch one in winter. Why? One theory is that shorter days and less sunlight mean less vitamin D, which results in weaker immune systems. Others believe that cold viruses survive better in cold, dry environments. Another thought is that we spend much more time indoors in the winter, meaning we breathe in more germ-filled recycled air. To fight off bugs this winter, ease up on alcohol, eat healthy, stay hydrated, get enough sleep, and, of course, wash hands often.Related:How to Boost Your Immune System
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Did you get enough sleep last night, or did you lose track of time and end up watching an entire season of your favorite TV show? One restless night isn't so bad, but don't make it a habit. Researchers from University of California, San Francisco, found that people who routinely clock fewer than six hours of sleep per night are four times more likely to catch a cold. The findings are available in this month's issue of Sleep.

While sleep deprivation has been linked to making people moody and unproductive, and leading to memory loss or mental health issues down the road, people still don't seem to get enough hours, prompting the CDC to deem sleep loss a "public health epidemic." For this study, researchers studied 164 volunteers between 2007 and 2011, using a watch sensor to track sleep quality and administering two months of health screenings and interviews to understand participants' stress levels, personalities, and lifestyle habits. After two months, volunteers were placed in a hotel and given the cold virus, then monitored for a week to see if they "caught" the cold.

Researchers believe that this methodology more accurately predicts a typical week for someone during cold and flu season, because it's based on their natural sleep patterns, as opposed to studies that purposefully deprive participants of sleep.

They found that subjects who had slept fewer than six hours a week the week before being given the virus were 4.2 times more likely to end up with a cold than those who slept at least seven hours. Those who slept fewer than five hours per night were 4.5 more likely to end up sick.

"Short sleep was more important than any other factor in predicting subjects' likelihood of catching cold," lead author Aric Prather said in a statement. "It didn't matter how old people were, their stress levels, their race, education, or income. It didn't matter if they were a smoker. With all those things taken into account, statistically sleep still carried the day."

Still not convinced you need an earlier bedtime? See five reasons you definitely need to catch more Zzs.