What kind of impact does diet have on immune system health?

The average American gets two to three upper respiratory infections each year, and one in five Americans comes down with the flu. While most people recover within a week or two, about 36,000 die from influenza-related complications and about 50,000 from respiratory infections (including pneumonia). On top of that, roughly 76 million cases of foodborne illnesses are reported each year, resulting in about 5,000 deaths. The bottom line: Human beings are greatly outnumbered when it comes to the bugs, viruses and bacteria that cause infections.

But fortunately, if you take some basic precautions—in terms of nutrition, exercise, sleep and hygiene—your robust immune system can protect you from the majority of these viral challenges.

If you have a deficiency of any nutrient, the immune cells will function less well. The immune system needs nutrients to do their work, and a regular diet should provide enough nutrients for the immune system to get along.

Studies show that children who are going through protein-calorie malnutrition in Africa suffer more infections of just about every variety, from gastrointestinal to lung and eye infections. People with anorexia nervosa show suppressed immunity and a higher rate of infections, pneumonia and other such ailments. They often die from lung infections.

Like any fighting force, the immune system army marches on its stomach. Immune system warriors need good, regular nourishment. Scientists have long recognized that people who live in poverty and are malnourished are more vulnerable to infectious diseases. Whether the increased rate of disease is caused by malnutrition's effect on the immune system, however, is not certain. There are still relatively few studies of the effects of nutrition on the immune system of humans, and even fewer studies that tie the effects of nutrition directly to the ability to fight off infectious disease.