W inter is here. And with it comes many viruses that can cause the flu, the common cold and other infections. While there’s no way to guarantee you won’t become sick, there are ways to build up your immune system and boost the odds that you’ll stay healthy.

Ward off the flu before it strikes. The flu is a more serious ailment than people think. More than 20,000 Americans die each year from the virus and its complications. What you can do...

Get a flu shot immediately -- if you haven’t already done so.

Myth: Many people believe that the flu shot causes the flu. It does not. Minimal flu-like side effects occur eight to 24 hours after vaccination in a small percentage of the population. If you do develop the flu after being vaccinated, your body was already incubating the virus.

Note: Those allergic to eggs and who have had other shots within the prior two weeks should speak with their doctors about whether the vaccine is safe for them.

Ask your doctor about the prescription medications amantadine (Symmetrel) and rimantadine (Flumadine). They can prevent the flu if you are exposed to the virus while the vaccine is kicking in... and they also effectively treat flu symptoms and shorten the course of the illness.

Start eating a healthier diet. Eating a total of at least seven servings of fruits and vegetables a day can boost the immune system. Wherever possible, get your vitamins in their natural form through foods instead of obtaining them through supplements. There is evidence that the vitamins in foods work in concert with other substances and with each other to convey a protective immune effect.

Helpful: 1,000 mg of vitamin C taken once a day may lessen the severity of the symptoms of respiratory infections. Don’t take more than that.

A recent report says that more than 1,000 mg of vitamin C offers no additional protection and makes people more vulnerable to kidney stones. While some people take vitamin C supplements all the time, I tell my patients to take them only when they are experiencing cold symptoms.

Important: Make sure your children eat healthy breakfasts -- consisting of fruit, milk and cereal -- every day. Even though it’s difficult to prevent your kids from playing with others who are ill, you can help boost their developing immune systems with a good diet.

Cut down on virus transmission. Colds are commonly spread through hand-to-hand contact with someone who is infected and has touched his/her mouth, eyes or nose.

The rhinovirus -- which is responsible for about 50% of all colds -- has been proven to live on inanimate objects (such as doorknobs, telephones and cups) for up to two or three days.

Self-defense: Wash your hands often and thoroughly. Hand washing can remove many of the viruses that cause these illnesses. Also: Encourage your children to wash their hands often.

You can also avoid infecting yourself and others by keeping your hands away from your eyes, mouth and nose... and avoiding contact with soiled napkins and tissues.

Airborne transmission is one of the most common ways the flu is spread, and it may also help to spread colds. Therefore, it’s best to sneeze and cough into a tissue (instead of your hands) and discard it immediately.

Avoid cigarette smoke. Smoking paralyzes the cilia -- the hairlike cells in the nasal and lung passages that help to keep them clear of infectious viruses and bacteria. This makes smokers even more susceptible to colds and other illnesses and prevents their immune systems from functioning at high levels.

There is also evidence that people who smoke recuperate more slowly from illness than nonsmokers. If you smoke, the best thing you can do is to stop, especially if you become sick.

Passive, secondhand smoke inhaled regularly also affects cilia. If you cannot avoid being around someone who smokes, ask him/her to put out the cigarette or to smoke somewhere else.

Exercise your stress away. People who are under high levels of psychological stress have twice the risk of catching colds. This may be due to the effect that stress has on the lining of the nasal cavities. Stress can cause the lining to swell and can make it more vulnerable to infection. Stress also lowers the immune system’s ability to fight off infection.

Stress is part of everyday life. While there’s no real way to avoid it, you can learn to control it, lessen it and deal with it better.

What you can do: People who exercise are better able to cope with stress. They have more energy and a lower incidence of illness, and they are better able to boost their immune systems.

Get enough sleep. People who feel tired and run down are also more vulnerable to illness. Make sure you -- and your children -- get the necessary amount of sleep.

Stay warm. While no studies confirm the connection between feeling chilly and illness, anecdotally there seems to be a connection.

My theory: Exposure to cold constricts blood vessels in the mucosa (the lining of the respiratory tract), making you more susceptible to infection and illness.

Always dress appropriately -- indoors and out.

Humidify your environment. While there is no guarantee that humidity and moisture help your body fight viruses like cold and flu, there is evidence that dry indoor air is a breeding ground for them.

Helpful: Leaving the bathroom door ajar while you shower helps humidify the air in the bedroom. So does placing pots of water atop radiators.

You may also want to invest in either a cold- or hot-air humidifier with a filter. Note: I prefer cold air. If you use a humidifier, be sure to clean it every other day with warm water and white vinegar. A dirty humidifier is a breeding ground for bacteria and mold.