Answers from Dr. Greene

QUESTION:

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

DR. ALAN GREENE:

Researchers at the National Heart and Lung Institute in the UK did a detailed analysis of the children aged 7 - 18 years, and found some very exciting results that were published in the August 2007 issue of Thorax. Unlike in America, 80% of the children in this study ate fresh fruit at least twice a day. And 68% ate vegetables at least twice a day. Those who ate fruits and vegetables enjoyed clear benefits. For the children in the study, eating grapes, apples, oranges, and fresh tomatoes all appeared to be protective against both wheezing and hay fever symptoms. Eating nuts (for those who are not allergic to them) also appeared helpful, cutting the odds of asthma symptoms in half.

On the flip side, eating trans fats every week, such as partially hydrogenated fats found in some margarines and fried and baked products, more than doubled the chance of asthma symptoms and more than doubled than chance of seasonal allergies. Overall, those who stuck closest to a traditional Mediterranean diet had a lower risk of symptoms of asthma, eczema, and seasonal allergies.

Taken together with earlier studies, these results are very motivating to help our kids learn to enjoy fresh fruits, vegetables, and nuts. Even once or twice a week appears to be significantly protective, compared to less often. And, of course, eating the recommended daily amounts is even better. Meanwhile, let’s wean our kids off trans fats and other ingredients that do nothing to help them thrive.

What Mom eats during pregnancy can also help protect her children from asthma and allergies, according to a study published in Thorax in June 2008. In particular, elementary school kids whose mothers had followed a Mediterranean diet during their pregnancy were less likely to develop asthma or allergies. Peers of these children were about twice as likely to have positive allergic skin tests, more than four times more likely to wheeze, and more than three times more likely to have both positive allergy tests and wheezing. What separates this study from others is that it was a forward looking (prospective) study. The researchers put forward their hypothesis in advance, and then followed families until the children were 6.5 years old. The participants weren’t aware that this study was about the Mediterranean diet when the data were being collected, to avoid introducing bias.

So what is a Mediterranean diet? The authors of this study defined it as a diet high in plant foods (fruits, vegetables, whole grain breads and cereals, legumes, and nuts), moderate amounts of dairy products and eggs, and very little red meat. The diet is also high in olive oil and fish.

Let’s consider some typical specific amounts:

• Two servings of fruit or fruit juice daily
• Fresh or cooked vegetables more than once a day
• Legume more than once a week
• Fish at least two or three times a week
• Whole grain as part of breakfast daily
• Pasta or rice at least five times a week
• Two dairy products (such as milk, cheese, or yogurt) daily
• Nuts two or three times a week
• Olive oil used daily
• Fast food less than once a week
• Sweets and pastries less than once a day

In this study, women received one point each if they ate above the median amount of vegetables, fruits and nuts, whole grain cereals, legumes, fish, and dairy products compared to all the women in the study. They also received one point if they ate below the average amount of red meat. The maximum possible score was 7. Those who scored at least 4 points enjoyed the dramatic benefits detailed above compared to those who scored 0 - 3.

In addition to the foods and styles of eating above, several specific nutrients have been associated with a lower asthma risk.

Kids who get plenty of vitamin D have a lower chance of asthma attacks, according to a study presented at the 2008 annual meeting of the American Academy of Allergy, Asthma, and Immunology. This study is preliminary, at best, but the results are consistent with a growing number of papers looking at how vitamin D might help prevent or reverse both asthma and eczema. Vitamin D, the sunshine vitamin, can be formed when the skin is exposed to sunlight or can be obtained in the diet. Some investigators even wonder if vitamin D deficiency is one of the explanations for the asthma epidemic in children in recent years. About 40% of American children get lower than optimum levels of vitamin D.

While these specific vitamin D benefits are not yet proven, the connection makes sense to me. We know that vitamin D acts on the smooth muscle cells in the airways and can help with some T cell problems in the immune system. Either way, it seems to me a good idea to make sure your young child is getting an adequate amount of vitamin D (the USDA Dietary Reference Intake is 200 IU daily throughout childhood, and I suspect that level will be raised in the next few years). [Editor's note: In 2010, the USDA raised the recommended daily allowance for vitamin D to 600 IU daily for those 1 - 70 years old.] This could be all the more important if your child has asthma, or if this condition runs in your family.

The role of omega 3 fats, including DHA, in preventing asthma is an active area of research. It makes sense to be sure kids are getting at least the recommended amounts of these healthful fats while the research continues.

Children with higher blood levels of important antioxidant nutrients may be less likely to develop asthma, according to a large study in the February 2004 issue of the 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% of vitamin C, beta carotene, and selenium levels 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 enjoy eating delicious whole foods -- fruits, vegetables, grains, nuts, and lean sources of protein.

Alan Greene, MD, FAAP, 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). He is a Clinical Professor of Pediatrics at the Stanford University School of Medicine.

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