BOSTON -- A lack of fruit and fish in teenagers' diets may keep them from attaining full lung capacity and set them up for later respiratory problems, researchers here said.
BOSTON, July 9 -- A lack of fruit and fish in teenagers' diets may keep them from attaining full lung capacity and set them up for later respiratory problems, researchers here said.
In a large cohort study, low fruit intake was associated with 1.3% lower lung function than predicted while low vitamin C intake was associated with the same degree of lung capacity impairment (both P?0.05), Jane S. Burns, Sc.D., of Harvard, and colleagues found.
Low intake of fruit, vitamin E, and n-3 fatty acid consumption was also linked to respiratory symptoms, including chronic bronchitis, wheezing and asthma, they reported in the July issue of the journal CHEST.
These relatively small effects were "not likely to have a functional impact on current respiratory health," the researchers said.
But, Dr. Burns added, "if these effects are being felt in the teen years when their lung function should be close to optimal levels, it's possible that they won't achieve their optimal levels and that the complaints of chronic bronchitis and wheeze may cause them to loose lung function by airway remodeling."
This "may have long-term consequences because lower pulmonary function in adults has been associated with increased morbidity and earlier mortality," the researchers noted.
Previous studies linking pulmonary function and symptoms to diet have focused on adults and children. So the researchers conducted the Teen Lung Study.
The study included 2,112 high school seniors in 13 communities across the United States and Canada during the 1998-99 school year.
Students completed questionnaires about respiratory symptoms, how often they ate various types of foods in the preceding year, whether they took vitamin supplements, and other factors. The researchers also tested each student's lung function.
Most of the students did not take multivitamins (72%) and did not meet recommended intake of fruit and vegetables (86%), vitamin E (89%), n-3 fatty acid (99.9%), or beta-carotene (58%).
Only 18% of the teens got less than the dietary reference intake of vitamin C, but much of it came from fortified drinks. A minority (39%) was also deficient in vitamin A intake by Institute of Medicine standards.
One-third of the cohort was overweight (body mass index at least 25 kg/m2), 24% reported smoking daily, and 89% were white.
Fruit intake in the lowest quintile below 0.25 servings a day, was associated with lower lung capacity as measured by forced expiratory volume in one second (FEV1 3.90 versus 3.96 L) compared with higher intake. The adjusted difference was significant (-1.3%, 95% confidence interval -2.4 to -0.2).
More students with low dietary fruit intake reported chronic bronchitic symptoms than did those with higher intake (26.8% versus 19.8%, odds ratio 1.36, P?0.05). Asthma also tended to be more commonly linked to low fruit intake, but the difference was not significant (10.9% versus 8.6%, adjusted OR 1.34, 95% CI 0.93 to 1.94).
Daily vitamin C intake in the lowest quintile below 85 mg, although in the range of the IOM-recommended 65 to 90 mg per day, was associated with:
"This suggests the current daily recommended intake for vitamin C may not be adequate to protect lung function," Dr. Burns and colleagues wrote.
Vitamin E intake in the lowest quintile below 5.2 mg per day was associated with an increased likelihood of reported asthma (11.6% versus 8.5%, adjusted OR 1.48, P?0.05) compared with higher intake.
Intake of dietary n-3 fatty acids in the lowest quintile below 22 mg was associated with:
Teen smoking in combination with low antioxidant vitamin C intake showed even greater risk for respiratory symptoms.
Although the study could not determine whether the associations seen were causal, micronutrient intake was similar for teens in the study as for those in the National Health and Nutrition Examination Survey III, "suggesting that these results may be generalizable."
Therefore, the findings suggest yet another reason for physicians to promote healthy eating among their teen patients, Dr. Burns said.
"I think that when you are dealing with a population that is very active like teens you can't count on them to eat enough fruit, fish, and antioxidant-containing foods," she said. "So the use of vitamin supplements is very helpful."
The researchers also pointed out that an observational study "cannot establish the temporal relationship between diet and respiratory outcomes. It may be that the critical period for diet's effect on the respiratory system is during early childhood when there is rapid differentiation and growth."