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Diet, Asthma Linked

Polyunsaturated fats tied to condition in toddlers

FRIDAY, July 20, 2001 (HealthDayNews) -- What do bread spreads have to do with asthma?

More than you think, say Australian researchers who found preschoolers who load up on polyunsaturated fats, the kind in margarine for instance, double their risk of developing the breathing disorder.

Scientists at Royal Children's Hospital in Melbourne looked at possible causes of asthma among 974 children, aged 3 to 5, in two Australian towns; 22 percent of the children in one town and 18 percent in the other had the condition. The study appears in the August issue of Thorax.

Well-established risk factors, such as allergies and a family history of asthma, roughly doubled a child's chances of having the condition, the researchers say. But so, too, did heavy consumption of polyunsaturated fats found in margarine, corn oil and other vegetable oils.

High fat intake could be responsible for as many as 17 percent of asthma cases in the study, say the researchers. They theorize that polyunsaturated fats may lead to an increase in the body's production of certain inflammatory molecules called prostaglandins, which could aggravate airways.

Fatty foods are also high in calories, and obesity has been linked to asthma.

But Joel Schwartz, a lung expert at the Harvard School of Public Health in Boston, says "there is some plausibility to there being an independent risk" of asthma from fat intake.

He says the reason lies with the old saw: You are what you eat. The outer walls of cells consist largely of fat, and the kind of fat they contain depends on the kind of fat you eat. In turn, cells produce different hormones based on the makeup of the cell wall.

"The kinds of prostaglandins that get manufactured depends on what's in the cell walls. That doesn't mean that [fat intake necessarily causes asthma], but it makes it plausible," Schwartz says.

Other studies have shown that people who eat diets rich in unsaturated Omega-3 fatty acids, such as in fish oil, are less prone to airway problems and may have stronger lung function, he says. Omega-3 fatty acids block the production of the same prostaglandins that polyunsaturated fats, which are high in Omega-6 fatty acids, promote.

On the other hand, children who were breast-fed as infants or who had at least three older siblings got significant protection from asthma, the study found. Breast-feeding is known to shield babies from allergies by passing on immunities from their mothers.

Since exposure to polyunsaturated fats is controllable, as is breast-feeding, the researchers suggest parents could reduce their child's risk of asthma by cutting back on one and doing more of the other. Indeed, not nursing might account for as many as 16 percent of the asthma cases among preschoolers in the study, they say.

One important trade-off is that polyunsaturated fats are thought to be gentler on the heart and vessels than animal fats, by building up less LDL, or "bad" cholesterol. On the other hand, polyunsaturated fats also lower the blood level of HDL, or "good" cholesterol, which protects the cardiovascular system.

Dr. Sally Wenzel, an asthma expert at National Jewish Medical and Research Center in Denver says she's not convinced by the study's findings.

For starters, she says the incidence of asthma among the children was extremely high, suggesting many did not truly have the condition. What's more, the researchers didn't have a very good gauge of how much fat the children ate.

"Rather than understanding the quality of the fat, you have to understand the quantity," Wenzel says.

Finally, although the study did find a protective effect from breast-feeding, recent evidence shows women with asthma who nurse may put their infants at greater risk for the disorder.

What To Do

Roughly 5 percent of American children under 18 suffer from asthma. Although treatable, acute asthma is estimated to cause about 5,000 deaths a year in the United States, says the National Institutes of Health.

To learn more about the disorder, try the Centers for Disease Control and Prevention .

For more on unsaturated fats, check the Heart Information Network or the American Heart Association.

SOURCES: Interviews with Sally Wenzel, M.D., professor, National Jewish Medical and Research Center, Denver; Joel Schwartz, Ph.D., associate professor, medicine and environmental epidemiology, Harvard School of Public Health, Boston; August 2001 Thorax
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