QUESTION:

Dr. Greene, is there any way to use nutrition to prevent asthma?

DR. ALAN GREENE:

What can you give a child to help prevent asthma? Asthma in children has more than doubled in the last decade, and quadrupled since 1973. Scientists are scrambling to understand the changes in our environments responsible for this rapid increase. One part of the environment gaining more attention is the tiny world that lives inside our own intestines. A typical healthy child might carry a pound or two of beneficial bacteria in their body - an entire ecosystem. These intimate neighbors form something like a neighborhood watch, helping us to respond well to dangerous strangers entering the body.

When trying to understand asthma and other allergic diseases, one of the key questions is, "What event might first trigger the allergy?" Allergies in humans always follow exposure to some allergen. But for most children, repeated exposure to many common allergens leads to increasing tolerance, not to increased allergies.

Researchers at the University of Michigan Medical School in Ann Arbor demonstrated one reason allergies might develop instead. Their elegant study appears in the January 2005 Infection and Immunity. They exposed mice to different allergens in the air, including egg protein and mold spores. The mice did not develop asthma, even with repeated exposure. But when some of the mice were given antibiotics that killed many of the beneficial bacteria in their guts, exposure to the same allergens did trigger allergic sensitization and wheezing. This held true in mice genetically predisposed to get asthma, and in those who were not. Breathing allergens did not trigger airway allergies in any of the mice except those whose gut bacteria had been damaged.

Other research has shown that giving pregnant and nursing moms' probiotics (beneficial bacteria such as those found in yogurts) results in decreased allergic skin disease in their children. Breastfeeding by itself promotes the growth of healthy bacteria within.

I suggest reserving antibiotic use in children for situations where the medicines are really important. I also suggest giving probiotics whenever antibiotics are given, to quickly replenish the bacteria within and to minimize antibiotic side effects. It also makes sense to me to minimize chemical preservatives and bleaches in what we give our children to eat and drink, and instead to give them a healthy variety of fresh whole foods.

There is another way to nurture healthy bacteria in the gut, beyond giving kids new bacteria (probiotics) and beyond avoiding destroying those they already have (antibiotics). Prebiotics are substances that promote the growth of healthy gut bacteria. They are found naturally in many foods, including bananas, whole wheat, garlic, onions, leeks, honey, tomatoes, chicory, and asparagus. In general, foods that are high in fiber, whether grains, legumes, greens and other vegetables, or berries and other fruits, tend to be foods that give valuable gifts beyond just good eating.

There are other benefits as well. Although childhood asthma has been increasing in recent years, children with higher blood levels of important antioxidant nutrients are less likely to develop asthma, according to a large study in the February 1, 2004, American Journal of Respiratory and Critical Care Medicine. The study looked at over 6,000 children aged 4 - 16 years. Separate analyses showed that those in the top 16 percent of vitamin C, beta carotene, and selenium in the blood tests were all 10 - 20% less likely to develop asthma than their peers.

Even more dramatically, high selenium levels cut the risk of asthma in half among children exposed to tobacco smoke. Selenium is found in many foods, including meat, seafood, eggs, bran, whole wheat, oats, walnuts, garlic, and brown rice -- it is often destroyed in food processing. Beta carotene gives yellow and orange fruits and vegetables their vibrant colors. It's also in green leafy vegetables. Getting it in the diet is far more effective than any vitamin or supplement.

Vitamin C is abundant in many foods, including citrus fruits, greens, broccoli, sweet potatoes, bell peppers, tomatoes, cantaloupe, and strawberries. This study is another good reason to help our children to enjoy eating delicious whole foods -- fruits, vegetables, grains, nuts, and lean sources of protein.

Alan Greene, M.D., earned a bachelor's degree from Princeton University and graduated from medical school at University of California at San Francisco. Upon completion of his pediatric residency program at Children's Hospital Medical Center of Northern California in 1993, he served as Chief Resident. During his Chief year, Dr. Greene passed the pediatric boards in the top 5% of the nation.

Dr. Greene entered primary care pediatrics in January 1993. He is on the Clinical Faculty at Stanford University School of Medicine where he sees patients and teaches Residents. He serves as the Chief Medical Officer of A.D.A.M., Inc., a leading provider of consumer health information, and helps direct A.D.A.M.'s editorial process. As A.D.A.M.'s CMO, he served as a founding member of Hi-Ethics (Health Internet Ethics) and helped URAC develop its standards for eHealth accreditation. He is also the Founder & CEO of DrGreene.com. Dr. Greene was also named Intel's Internet Health Hero for children's health. He is an author, medical expert, and a media personality.

Dr. Greene is the author of Raising Baby Green (Wiley Books, 2007), From First Kicks to First Steps (McGraw-Hill, 2004), and The Parent’s Complete Guide to Ear Infections (Avon Books, 1997). He is also a co-author of The A.D.A.M. Illustrated Family Health Guide (A.D.A.M., Inc., 2004).Dr. Greene has appeared in numerous publications, including the Wall Street Journal, Parenting, Parent, Child, American Baby, Baby Talk, Working Mother, Better Home's & Gardens, and Reader's Digest. He also appears frequently on television and radio shows as a medical expert.