The relation between dietary intake of individual fatty acids, FEV1 and respiratory disease in Dutch adults.

BACKGROUND: A reduced dietary intake of n-3 fatty acids, in association with increased n-6 fatty acid intake, has been proposed as a potential aetiological factor for chronic obstructive pulmonary disease (COPD) and asthma. However, the relative importance of individual fatty acids within the n-3 and n-6 categories on this effect has not been widely investigated. We have studied the relation between individual fatty acid intakes, lung function and self-reported respiratory symptoms and diagnoses in a representative sample of more than 13,000 Dutch adults. METHODS: Intake of individual fatty acids was estimated by a food frequency questionnaire and analysed in relation to measures of forced expiratory volume in 1 s (FEV1) and to questionnaire reported wheeze, asthma and COPD symptoms. RESULTS: After adjusting for confounding, we found no protective association between individual n-3 fatty acid intakes and FEV1. Higher intakes of some n-6 fatty acids were associated with lower FEV1, this effect being most marked for c22:4 n-6 docosatetraenoic acid (reduction in FEV1 between the highest and lowest quintile of intake 54.5 ml (95% CI -81.6 to -27.4)). Most of the n-6 fatty acid effects interacted significantly with smoking, their effects being strongest in current smokers. Individual n-3 fatty acid intakes were generally associated with a higher risk of wheeze in the past year, but otherwise there was little or no association between fatty acid intake and wheeze, doctor diagnosed asthma or other respiratory symptoms. CONCLUSIONS: A high intake of n-3 fatty acids does not appear to protect against COPD or asthma, but a high intake of several n-6 fatty acids is associated with a significant reduction in FEV1, particularly in smokers. These findings indicate that high dietary intake of n-6 fatty acids, rather than reduced n-3 intake, may have an adverse effect on lung health.

Lung function and blood levels of copper, selenium, vitamin C and vitamin E in the general population.

BACKGROUND: Increased dietary intake of antioxidants has been associated with higher lung function, but few studies have used biological markers of antioxidant intake. OBJECTIVE: This study aimed to determine if antioxidant status, as measured by blood levels, influences lung function. DESIGN: Using a random subsample of 479 participants, aged 18-65 y old, from a larger cross-sectional observational study, the association of forced expiratory volume in 1 s (FEV1) with plasma copper, vitamin C, vitamin E and serum selenium was assessed. RESULTS: An s.d. increase in blood copper level was associated with a difference in FEV1 of -48 ml (95% confidence intervals: -95, -2 ml, P = 0.04), vitamin C +49 ml (+4, +94, P = 0.03), vitamin E -15 ml (-62, +32, P = 0.53) and selenium +52 ml (+7, +96, P = 0.02). The sizes of association were not appreciably altered in a mutually adjusted model. CONCLUSIONS: Higher levels of serum vitamin C and selenium appear to be associated with higher FEV1. The association between higher serum copper and lower FEV1 requires further study in view of the ubiquitous exposure to this mineral.

A case-control study of dietary and erythrocyte membrane fatty acids in asthma.

BACKGROUND: Epidemiological evidence suggests that increased dietary omega-6 and reduced omega-3 fatty acid intake, may have contributed to the rising prevalence of asthma, but these hypotheses have not been tested in studies comparing both dietary intake and objective measures of polyunsaturated fatty acids. OBJECTIVE: To assess whether a higher intake of omega-6 or a lower intake of omega-3 fatty acids increases the risk of asthma, by measuring dietary fatty acid intake by a food frequency questionnaire (FFQ) and erythrocyte membrane fatty acids, as an objective biomarker of intake. METHODS: We have compared individual fatty acid intake estimated by FFQ and by mass spectrometry of fasting erythrocyte cell membranes in 89 cases of asthma and 89 community-matched controls. RESULTS: The odds of asthma were increased in relation to intake of the omega-3 fatty acids eicosapentaenoic acid (odds ratio (OR) for difference between the 25th and 75th centiles of intake= 1.89, 95% CI 1.15-3.11) and docosahexaenoic acid (OR = 2.11, 95% CI 1.19-3.74). There was no evidence of any difference in erythrocyte membrane levels of omega-3 fatty acids, while the odds of asthma were reduced in relation to linoleic acid (omega-6) membrane levels (OR = 0.45, 95% CI 0.21-0.95). CONCLUSION: These findings suggest that dietary omega-3 fatty acids do not play a major role in protecting against asthma, and that higher levels of erythrocyte membrane linoleic acid are associated with a lower risk of asthma.

Vitamin E supplements in asthma: a parallel group randomised placebo controlled trial.

BACKGROUND: Increased dietary vitamin E intake is associated with a reduced incidence of asthma, and combinations of antioxidant supplements including vitamin E are effective in reducing ozone induced bronchoconstriction. A study was undertaken to investigate the effect of supplementation with vitamin E for 6 weeks on bronchial hyperresponsiveness in atopic adults with asthma. METHODS: 72 participants from a clinical trial register of adults with asthma were randomised to receive 500 mg natural vitamin E or matched placebo for 6 weeks in a placebo controlled, double blind parallel group clinical trial. Inclusion criteria included age 18-60 years, maintenance treatment of at least one dose of inhaled corticosteroid per day, a positive skin prick test to one of three common allergens, and bronchial hyperresponsiveness to methacholine (defined as a dose provoking a 20% fall in forced expiratory volume in 1 second (FEV(1)) (PD(20)) of 12.25 micromol). Secondary outcomes were FEV(1), forced vital capacity, mean morning and evening peak flow, symptom scores, bronchodilator use, and serum immunoglobulin E levels. RESULTS: In the primary intention to treat analysis the change in PD(20) was similar in the vitamin E and placebo groups with a mean difference of +0.25 doubling doses of methacholine (95% confidence interval -0.67 to +1.16 greater with vitamin E). There was no effect of vitamin E supplementation on any other measure of asthma control, either in the intention to treat or per protocol analysis. There was also no effect of vitamin E supplementation on serum immunoglobulin levels. CONCLUSION: Dietary supplementation with vitamin E adds no benefit to current standard treatment in adults with mild to moderate asthma.

Oral magnesium and vitamin C supplements in asthma: a parallel group randomized placebo-controlled trial.

BACKGROUND: Epidemiological studies suggest that higher intakes of dietary vitamin C and magnesium may be associated with a reduced risk of asthma. OBJECTIVE: To determine whether vitamin C or magnesium supplements improve the clinical control of asthma in primary care patients. METHODS: A randomized, placebo-controlled, double-blind parallel group trial of 16 weeks supplementation with 1 g/day vitamin C, 450 mg/day magnesium chelate or matched placebo. Three hundred patients aged 18-60 years with physician-diagnosed asthma, controlled with at least one dose of an inhaled corticosteroid daily, were recruited from 24 primary care practices in Nottingham, UK. The main outcome measures were change in forced expiratory volume in 1 s, forced vital capacity, airway responsiveness to methacholine, mean morning and evening peak flow, symptom scores and bronchodilator use, both individually and as a combined summary statistic. RESULTS: There was no evidence of any beneficial effect of either supplement on any outcome measure of asthma control in the primary intention-to-treat analysis, or in an analysis restricted to participants who completed the study. CONCLUSIONS: Regular dietary supplementation with vitamin C or magnesium adds no clinical benefit to current standard therapy of asthma in primary care patients.

Combined effects of aerobiological pollutants, chemical pollutants and meteorological conditions on asthma admissions and A & E attendances in Derbyshire UK, 1993-96.

BACKGROUND: The effect of outdoor aeroallergen exposure in asthma may be enhanced by air pollutants, including ozone, nitrogen dioxide and particulates, and by certain weather conditions. It is not yet established whether these interactions are important in determining asthma morbidity at the population level. OBJECTIVE: We have investigated the joint effects of aeroallergens, rainfall, thunderstorms and outdoor air pollutants on daily asthma admissions and Accident and Emergency (A & E) attendance using routinely collected data between 1993 and 1996 from Derby in central England. METHODS: Daily counts during the aeroallergen season of grass and birch pollen, basidiospores, Didymella, Alternaria and Cladosporium, maximum 1 hour ozone and nitrogen dioxide and daily average black smoke measurements, all made in the vicinity of the city centre, were categorized in tertiles. Rainfall was classified as dry, light ( 2 mm). The modifying effect of outdoor pollutant levels, and rainfall or the occurrence of a thunderstorm, upon the effects of individual aeroallergens on asthma admissions and A & E attendance were investigated by fitting appropriate interactions in log linear autoregression models with adjustment for potential confounders. RESULTS: We found a significant interaction between the effects of grass pollen and weather conditions upon A & E attendance, such that the increase with grass pollen count was most marked on days of light rainfall (adjusted rate ratio for >/= 50 vs < 10 grains/m3 at lag 2 days = 2.1, 95% CI 1.4, 3.3). Asthma admissions increased with Cladosporium count. We found no statistically significant interactions between effects of any individual aeroallergen and outdoor air pollutant upon either measure of asthma morbidity. CONCLUSIONS: Rainfall and thunderstorms are important effect modifiers in the relation between grass pollen and measures of acute asthma morbidity. Interactions between ambient levels of aeroallergens and chemical pollutants in the Derby area do not play a major role in determining asthma admissions and A & E attendance.

Human selenite metabolism: a kinetic model.

A model is developed to describe the kinetics of sodium selenite metabolism in humans, based on plasma, urine, and fecal samples obtained from six subjects over a 4-wk period after a single oral 200-micrograms dose of the enriched stable isotope tracer 74Se. The model describes absorption, distributed along the gastrointestinal tract, and enterohepatic recirculation. The model includes four kinetically distinct plasma components, a subsystem consisting of the liver and pancreas, and a slowly turning-over tissue pool. For the six subjects, the ranges of mean residence times for the four plasma components are, respectively, 0.2-1.1 h, 3-8 h, 9-42 h, and 200-285 h; for the hepatopancreatic subsystem 4-41 days; and for the tissue pool 115-285 days. Approximately 84% of the administered dose was absorbed, and after 12 days approximately 65% remained in the body. The model predicts that after 90 days approximately 35% of this Se would be retained, primarily in the tissues. Separating Se metabolism into several distinct kinetic components is a first step in identifying the efficacious, nutritious, and toxic forms of the element.

Copper, iron, zinc, and selenium dietary intake and status of Nepalese lactating women and their breast-fed infants.

The dietary intake of copper, iron, zinc, and selenium of 26 Nepalese lactating mothers was estimated from chemical analysis of 24-h food and beverage composites. Fasting blood and milk samples were obtained from the mothers and blood samples were obtained from the infants. The Nepalese mothers consumed significantly more Cu, significantly less Fe and Se, and similar amounts of Zn as compared with American lactating women. Blood Fe status indices and plasma concentrations of Cu, Zn, and Se were lower in the Nepalese mothers than in the American mothers. These lower values may in part be related to the high neutral detergent fiber and phytate content of the Nepalese diet, which could make these minerals less available for absorption. The high exposure to infections in Nepal may also depress Fe status indices and plasma Zn concentrations. The lower dietary Se intake of the Nepalese mothers was reflected in lower milk concentrations.

Determination of selenium in biological matrices.

The definitive IDMS method has the advantage of good detection limits and precision. The advent of the new, smaller, easy-to-use GC/MS system should make this method more popular. The fluorometric method remains the method of choice for the determination of selenium in many matrices if the limitations of the method are understood. The newer methods include gas chromatography, HG-AAS, and GFAAS. The gas chromatography methods show promise because of the relatively simple instrumentation needed and the fact that the analyte is separated from the matrix. HG-AAS offers good sensitivity provided care is taken to ensure complete sample digestion and conversion of selenium to selenite. The advent of Zeeman background correction systems for GFAAS has greatly facilitated selenium determinations, particularly in biological matrices where iron and phosphorus are also present. The reference materials now available, used as part of a quality assurance program, should help to ensure accurate determinations, permit method validation, and allow performance evaluation in interlaboratory trials.

Outcome of pregnancy in the rat with mild hyperphenylalaninaemia and hypertyrosinaemia: implications for the management of "human maternal PKU".

In attempting to determine the effects of mildly elevated maternal phenylalanine (Phe) blood levels on the developing fetal rat brain, a dietary supplement of Phe was given, under taste cover of Aspartame. Phe and tyrosine (Tyr) levels were mildly elevated throughout pregnancy without evidence of malnutrition. Mild hyperphenylalaninaemia with concurrent hypertyrosinaemia induced in rats prior to conception resulted in microcephaly and lasting behavioural problems in the offspring, specifically hyperactivity and learning difficulties. Dams fed Tyr to produce Tyr levels equivalent to the Phe-fed animals showed only the learning difficulties among the offspring. alpha-Methyl Phe, a Phe hydroxylase inhibitor, fed in conjunction with Phe, at the level relevant to these experiments, resulted in raised Tyr levels and does not provide a better method of determining whether mildly elevated maternal Phe levels alone, or Phe and Tyr in combination, cause the abnormality found in the offspring of Phe-supplemented dams. Therapeutic addition of Tyr to diets of mothers with even mild hyperphenylalaninaemia should be approached with caution as mild co-elevation of Phe and Tyr in the fetus may be harmful. In the face of such a possible therapeutic dilemma alternatives, such as dietary additions of other essential amino acids to limit fetal brain damage, need to be explored.