Foods

• Antioxidant-rich foods build strong immune systems.side salad image by Shirley Hirst from Fotolia.com
  
  Our immune system needs antioxidants (beta-carotene, selenium, vitamins C and E, and zinc) to bolster its best defense against bacteria, fungus, parasites and viruses. The best sources of antioxidants are brightly colored fruits (such as tomatoes and watermelon), teas (especially organic green tea) and vegetables (broccoli, carrots and spinach) either eaten raw or lightly steamed.
  
  Saturated fat and sugar weaken immune function. Just a couple of sodas can impede white blood cells from destroying bacteria for hours.
  
  

Vitamin D3

• The "sunshine" vitamin, D3, triggers T cells to fight infections.a beautiful bronze blond woman enjoying the sun image by L. Shat from Fotolia.com
  
  University of Copenhagen scientists uncovered that T cells, our weapon against infections, depend on vitamin D3 to kill bacteria and viruses. Low levels of vitamin D are associated with cancer, colds and flu, diabetes, heart disease, infections and multiple sclerosis.
  
  Investigators discovered that 1,000 international units (IU) of vitamin D3 per day can reduce the risk of breast and ovarian cancer by up to 50 percent. Experts recommend 2,000 IU of vitamin D3 daily for adults.
  
  

Moderate Exercise

• Regular exercise strengthens immune function and reduces the risk of death.grandfather bike riding with grandson image by itsallgood from Fotolia.com
  
  Walking for 30 minutes a day can increase levels of leukocytes, which are the cells that fight infections. Researchers revealed that people who regularly get moderate exercise show reduced death rates from all causes compared to sedentary individuals. Controlled, randomized studies show that women who take a brisk 45-minute walk on five days a week have 1/2 as many sick days due to colds as sedentary people.
  
  

Stress

• Chronic stress can wear down the immune system.stress image by Andrii IURLOV from Fotolia.com
  
  While moderate exercise improves immune function, too much exercise actually interferes with it. Other kinds of stress also can weaken the immune system. Short-term stress can stimulate immune function, but chronic stress has the opposite effect.
  
  Research reveals that meditation strengthens immune function. People who meditated for a couple of months produced more antibodies after a flu vaccination than people who didn't meditate, and that enhanced immune function still worked four months later.
  
  

Relaxation

• Laughing, meditating and enough sleep support a strong immune system.Laughter image by Stepanov from Fotolia.com
  
  Like meditation, other types of relaxation enhance immune function. Laughter decreases stress hormones while increasing the white blood cells that fight infections. Scientists also discovered that laughing increases endorphins and growth hormones that boost immune function.
  
  In contrast, a lack of sleep tends to harm immune function. When university students were limited to four hours of sleep, they could only generate 1/2 the normal amount of antibodies following a flu vaccination.