Good Nutrition Vital to Maintain Healthy Immune System
Sharon Palmer, R.D.
Environmental Nutrition Newsletter
Foods that power up your immune defense are a hot marketing tool. From products like breakfast cereals and dietary supplements that claim to "support immunity" to magazine articles that recommend top "immune superfoods," it seems like the idea of eating to boost immune function is everywhere. Perhaps it's a good thing, as infectious diseases are the leading cause of morbidity in the world. But is there truth behind the hype?
THIS IS YOUR IMMUNE SYSTEM
You can credit your immune system for allowing you to thrive within a busy, interactive world. The immune system is your body's protective network that fends off invasion by harmful substances, such as bacteria, viruses, and chemicals, as well as guarding against the development of cancer.
When your immune system is healthy, you have multiple barriers to protect against invaders, including your skin, inflammatory responses, and specific immune responses, such as certain types of white blood cells that destroy pathogens.
Your gut plays a very important role in your immune system; it's the largest immune organ in the body, accounting for 25 percent of your immune cells. More than 400 species of bacteria reside in the gut, and they have important symbiotic (beneficial) relationships with your body.
As you age, your immune system diminishes. Speaking at a 2009 Tufts Seminar on nutrition and immunity, Meydani reported that there is an increased incidence of infectious disease (and morbidity and mortality from infectious disease) in older adults because they're more susceptible, the pathogens are more virulent, and there's a negative change in the gut bacteria. To top it off, marginal nutritional deficiencies related to diet also are common in older adults.
And once you have an infection, a vicious cycle kicks in: The infection obstructs your ability to boost nutrition because of loss of appetite, fever, and diarrhea, thus your immune system weakens. To make matters worse, scientists now know that nutritional deficiencies can cause a virus to become more virulent.
NUTRITION AND THE IMMUNE SYSTEM
One of the most important ways to maintain a healthy immune system is to power up on good nutrition.
"When a pathogen enters the body, the immune system recognizes it and the body produces an army of specialized immune cells to get rid of the pathogen," explains Meydani. And what do the immune cells need in order to grow in numbers?
"Essential nutrients like vitamins, minerals, amino acids and essential fatty acids," she adds. This is the root of the diet-immunity connection. "Nutrients are essential for the optimal function of the immune response and to prompt a defense against pathogens. Deficiencies of nutrients, as well as aging, can impair the host's defense and increase the occurrence of pathogens," says Meydani.
The following foods and nutrients show promise for their positive effects on the immune system:
1. Vitamin C: Many people believe fervently that vitamin C boosts their immune function and helps fight colds. Unfortunately, the science has been far from concrete, with some studies showing that it enhances immune function, and other studies showing no effect. According to the
2. Vitamin E: Its documented role in the immune system has led immunology researchers to study vitamin E. In a 2004 study led by Meydani and published in 2004 in The Journal of the
3. Zinc. Studies show that people with low serum zinc levels experience twice the frequency of pneumonia (as well as longer duration and more antibiotic use,) compared with those who have adequate zinc levels, according to Meydani.
In a 2007 study in the
4. Vitamin D. While the evidence isn't strong, scientists recognize that the sunshine vitamin may have important functions within the immune system. Research shows that patients with tuberculosis respond better when treated with vitamin D or sunlight. In addition to sunlight, you can find vitamin D in fortified dairy products and mushrooms, salmon and sardines.
The potential immune benefits of calorie restriction have attracted the interest of researchers. In the CALERIE Study (Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy Study,) overweight participants divided into two groups reduced their calorie intake by 10 percent and 30 percent, for six months, resulting in significant improvements in immune response in both groups, with the best effects seen in the 30 percent group.
"I'm not recommending that people who are not overweight would benefit from calorie restriction. Eat enough, but not too much," urges Meydani. If you decrease calories too much and it results in nutritional deficiencies, it's not good for the immune system.
These live microorganisms can exert health benefits by improving the number of beneficial bacteria in the gut.
"Several studies show that the right types of probiotics increase the immune response," says Meydani.
A study in the 2007 issue of
Mushrooms. Curiously, mushrooms have captured scientists' attention in immune research. When mice were fed a powder made of white button mushrooms, the natural killer cell activity increased significantly, according to a 2007 study published in
A WHOLE FOOD APPROACH
So should you take mega-doses of essential nutrients to boost your immune system?
"We can't say with certainty. Sometimes if you supplement at more than the required level of nutrients, the immune function can decrease. It's not always the case that more is better," says Meydani. In addition, nutrients appear to impact people's immune systems differently. Meydani explains that people can be "responders" or "nonresponders" to particular nutrients, based on genetic differences.
Many food companies and the media have made overly exuberant claims about the ability of particular foods to power up your immune system. It's important to keep in mind that foods contain a synergy of nutrients that work in unison to provide health benefits vs. supplements which only provide one or two nutrients.
The best approach for fostering a healthy immune system is to eat a nutrient-rich diet that meets all of your body's needs. Here's more reason to make every bite count, with delicious, whole foods bursting with nutrients.
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