Here in the northern latitudes, the incidence of colds, flu, pneumonia, strep, chicken pox, and norovirus infections (“stomach flu”) — rises dramatically during the winter months.
We even suffer more (and more damaging) heart attacks and strokes  during winter.
Why do we fall prey to these infections and cardiovascular events more often in winter, anyway?
It turns out the answers are complex, elusive, and still evolving.
For a long time, experts told us we catch more colds and flu in winter because we huddle together indoors in poorly ventilated surroundings, especially school children who then pass the infections along to their families.
Skeptical scientists have since proposed many other theories, which may interact and overlap in complex ways. They range from shorter day length, Vitamin D deficiency  (either or both of which may alter hormone balance, which in turn lowers immune response), climate and weather factors, physiological responses to exposure to chilly air, and the properties of some viruses themselves, which favor transmission in cold air and low humidity . Furthermore, the dry winter air can slow the normal process of cleaning the nasal mucous linings and drying them out, making them more susceptible to infection.
Take care of yourself
Regardless of the cause, research has confirmed the value of many self-care practices for helping ward off winter infections. Most of them won’t surprise you.
- Wash your hands —often. Most epidemiologists cite frequent handwashing as the number one defense against colds and many other common winter bugs. Effective handwashing means 20 seconds of vigorous rubbing with plain soap and water.
- Humidify inside and out. Keep your body well hydrated and your indoor air humidified. We add moisture to the air of our wood-heated home by hanging laundry indoors , keeping a lot of houseplants, and setting steamers on the stoves that release moisture gradually into the surrounding air.
- Exercise. Studies show that exercise boosts the immune system  to help your body fight infection. One caution: If you have a fever or anything more serious than a light cold, rest up and lay off the exercise.
- A corollary: Get outdoors more often, especially in midday. Many of us hidebound northerners experience a better mood and a boost in energy when we get out on cold, sunny winter days. I’ve found that investing in full-spectrum (mimics the wavelengths in natural sunlight) compact fluorescent lights throughout my house goes a long way towards staving off winter depression (low energy, food cravings, lack of enthusiasm). Some scientists believe that daily exposure to full-spectrum light helps boost immune function, too.
- Eat your vegetables. Increase your daily intake of green, red, yellow and white vegetables. A growing body of research  reveals that eating more and a greater variety of vegetables and fruits improves immune function . The big bonus: It’s one food group you can’t overdose on.
- Get enough sleep. Research confirms the value of a good night’s sleep . Sleeping well reduces your chances of heart problems and other chronic diseases, improves immune function, and even helps prevent obesity. Don’t brag about how little sleep you need. Get your z’s.
- Reduce stress. Stress weakens the immune system , and winter adds several layers of stress for most of us: (e.g., dealing with storms and power outages, sick kids, less daylight, snow shoveling, and the sometimes-overwhelming demands of the winter holidays--including financial stress. Make this your season to explore stress-reducing strategies .
- Keep holiday food safe . Foodborne illnesses sicken 48 million Americans each year. Avoid becoming one of them.
- Bone up on tips for preventing winter heart attacks .
Also Yes! to a seasonal flu shot. Yes! to staying away from sick people (good luck!). Many people take supplements of vitamin D, vitamin C, echinacea, and other products reputed to boost immunity. Please check with your doctor or other trusted health-care source before you try any new herb or vitamin supplement.
Next post: If you do come down with something, don’t get down on yourself. Take action.
Margaret Boyles lives in a wood-heated house in central New Hampshire. She grows vegetables, eats weeds, keeps chickens, swims in a backyard pond in summer, snowshoes in the surrounding woods in winter, and commutes by bike whenever possible.