Karen Webb

Validity and reproducibility of a self-administered food frequency questionnaire in older people

This study assesses the validity and reproducibility of a 145‐item self‐administered food frequency questionnaire (FFQ) in a representative older population aged 63 to 80. Semi‐quantitative FFQs were completed by 89% of 3,654 residents attending a community‐based eye study in Sydney, Australia. The FFQs validity was assessed against three, four‐day weighed food records (WFRs) completed four months apart by 79 people. A further 152 subjects completed a repeat FFQ about a year after the baseline FFQ, of whom 131 completed a second repeat FFQ about six weeks later. Both short and long‐term reproducibility of the FFQ were assessed using data from these subjects. Comparison of the FFQ with the average of the three, four‐day weighed food records resulted in energy‐adjusted Spearman correlations above 0.5 for most of the nutrients. The proportion of subjects correctly classified to within one quintile category for each nutrient intake ranged from 57% for zinc to 82% for vitamin C, with most nutrients correctly classified within one quintile for about 70% of subjects. Quadratic weighted kappas were reasonable, between 0.3 and 0.5 for most nutrients. The FFQ was highly reproducible in the short term, with correlations for most nutrients about 0.70 to 0.80 and acceptably reproducible in the longer term, with correlations mostly 0.60 to 0.70. The results verity that it is possible to use relatively simple, but comprehensive, self‐administered FFQs to study nutrient exposures in large‐scale epidemiological studies of the elderly and to expect reasonably high FFQ response rates.

Use of self-report to monitor overweight and obesity in populations: some issues for consideration.

Objective : To examine the validity of self‐reported height and weight data reported over the telephone in the 1997 NSW Health Survey, and to determine its accuracy to monitor overweight and obesity in population surveys.

Dietary antioxidant intake and incidence of Early age-related maculopathy: The Blue Mountains Eye Study

OBJECTIVE To investigate associations between dietary intake, including modest supplement intake, of antioxidant vitamins and zinc at baseline and the 5-year incidence of early age-related maculopathy (ARM). DESIGN Population-based cohort study. PARTICIPANTS From 1992 through 1994, 3654 persons aged 49 years or more (82% of those eligible) living in two postcode areas west of Sydney, Australia, were examined for the Blue Mountains Eye Study baseline. Five years later, 2335 persons (75% of known survivors) were reexamined. METHODS A 145-item Food Frequency Questionnaire (FFQ) was used to assess nutrient intakes. Of the 2335 people who attended a follow-up visit, 1989 (85%) had completed a FFQ at baseline. The nutrients examined in this study included: alpha-carotene, beta-carotene, beta-cryptoxanthin, lutein and zeaxanthin, lycopene, retinol, vitamin A, vitamin C, and zinc. MAIN OUTCOME MEASURES Early ARM was assessed by masked grading of stereo retinal photographs. Definitions for incidence closely followed those used in the Beaver Dam Eye Study. RESULTS Early ARM developed in 192 persons (8.7% 5-year incidence) who did not have either late or early ARM at baseline. Of these, 159 persons completed the FFQ at baseline. After adjusting for age, gender, family history of ARM, and smoking status at baseline, no associations, or any trends suggesting possible association, were found between baseline intake of the nutrients examined, apart from vitamin C, and the 5-year incidence of early ARM. Compared with the lowest quintile, increasing baseline intakes of vitamin C, from diet and supplements, was associated with an increased risk of incident early ARM (odds ratio [OR], 1.7; 95% confidence interval [CI], 1.0-3.0; and OR, 2.3; 95% CI, 1.3-4.0 for the fourth and fifth quintiles, respectively). CONCLUSIONS Our cohort study of an older population could not find evidence of protection associated with usual dietary antioxidant or zinc intakes (including use of supplements) on the 5-year incidence of early ARM.

The Childhood Asthma Prevention Study (CAPS): Design and Research Protocol of a Randomized Trial for the Primary Prevention of Asthma

The Childhood Asthma Prevention Study is a randomized controlled trial to measure whether the incidence of atopy and asthma can be reduced by house dust mite allergen reduction, a diet supplemented with omega-3 fatty acids, or a combination of both interventions. Six hundred and sixteen pregnant women whose unborn children were at high risk of developing asthma because of a family history were randomized prenatally. Study groups are as follows: Group A (placebo diet intervention, no house dust mite reduction), Group B (placebo diet intervention, active house dust mite reduction), Group C (active diet intervention, no house dust mite reduction), and Group D (active diet intervention, active house dust mite reduction). The house dust mite reduction intervention comprises use of physical and chemical methods to reduce allergen contact. The dietary intervention comprises use of a daily oil supplement from 6 months or at onset of bottle-feeding, and use of margarine and cooking oils based on sunflower or canola oils to increase omega-3 dietary intake. Data is collected quarterly until the infant is 1 year old and then half yearly until age 5 years. Questionnaires are used to collect respiratory illness history and information about diet and home environment. Dust is collected from the childs bed and bedroom and playroom floors. Blinded assessments are conducted at 18 months, 3 years, and 5 years. Skin prick tests to common allergens, blood tests, and detailed illness, medication use, and vaccination histories are collected. Primary outcomes will be the development of allergic sensitization and the presence and severity of asthma. This study is designed to measure the effectiveness of allergen reduction and dietary supplementation, both separately and in combination, for the primary prevention of atopy and asthma. The results of this study may have important implications for public health policies to reduce the incidence of childhood asthma. Control Clin Trials 2001;22:333-354

Consumption of 'extra' foods by Australian children: types, quantities and contribution to energy and nutrient intakes

Objective:To measure the types and quantities of energy-dense, nutrient-poor ‘extra’ foods consumed by Australian children and adolescents and their contribution to total energy and nutrient intakes.Design, setting and subjects:We used data from 3007 children, aged 2–18 years, who participated in the nationally representative 1995 National Nutrition Survey. Intake was determined by 24-h recall and ‘extra’ foods were defined using principles outlined in the Australian Guide to Healthy Eating (AGHE) and by applying cut points for maximum amounts of fat and sugar within each food category.Results:All children (99.8%) consumed at least one ‘extra’ food and the most commonly consumed were margarine, sugar-sweetened soft drinks, cordials and sugar. ‘Extra’ foods contributed 41% of daily energy intake. Those foods contributing most to energy intake were fried potatoes (4.2%), sugar-sweetened soft drinks (3.3%), ice cream/ice confection (3.1%) and cordials (2.7%). Age and sex were important determinants of ‘extra’ food intake, with males and older children generally consuming more and different types of, ‘extra’ foods than females and younger children. ‘Extra’ foods contributed 19% protein, 47% total fat, 47% saturated fat, 54% sugar, and approximately 20–25% of selected micronutrients to the diet. Calcium and zinc intakes from core foods were below 70% of the recommended dietary intakes for adolescent girls.Conclusions:‘Extra’ foods are over-consumed at two to four times the recommended limits and contribute excessively to the energy, fat and sugar intakes of Australian children, while providing relatively few micronutrients. This is of concern in terms of childrens weight and nutrient status.Sponsorship:DR was on placement at NSW Centre for Public Health Nutrition as part of the NSW Health Biostatistical Officer Trainee Program.

The association between infant feeding practices and subsequent atopy among children with a family history of asthma.

Background Although longer duration of breastfeeding and later introduction of solid foods are both recommended for the prevention of asthma and allergic disease, evidence to support these recommendations is controversial.

Dietary antioxidants and age-related maculopathy: the Blue Mountains Eye Study.

OBJECTIVE To assess associations between the stages of age-related maculopathy (ARM) and dietary intake of carotene, vitamin C, retinol, and zinc. DESIGN Cross-sectional, population-based study. PARTICIPANTS A total of 3654 subjects 49 years of age and older from a defined area, west of Sydney, Australia, participated. A total of 2900 participants (79.4%) completed accurate food records. INTERVENTION Masked grading of stereoscopic macular photographs, detailed interviewer-administered questionnaire, and 145-item self-administered food frequency questionnaire. MAIN OUTCOME MEASURES Late ARM and early ARM were diagnosed from photographic grading. RESULTS The authors found no statistically significant associations between ARM and dietary intake of either carotene, zinc, or vitamins A or C, either from diet or supplements or from the combined intake from diet and supplements. Multivariate-adjusted odds ratios (95% confidence interval) were calculated comparing highest to lowest dietary intake quintiles. For late ARM, the odds ratios were carotene, 0.7 (range, 0.3-2.0); vitamin A, 1.2 (range, 0.5-3.3); vitamin C, 1.3 (range, 0.5-3.4); and zinc, 1.0 (range, 0.4-2.8). For early ARM, the odds ratios were carotene, 0.7 (range, 0.4-1.1); vitamin A, 1.2 (range, 0.7-2.0); vitamin C, 0.9 (range, 0.5-1.4); and zinc, 0.8 (range, 0.5-1.3). No significant trends were apparent. Adjustment for energy intake also showed no associations between these antioxidants and ARM. Further, no associations were found between increasing intake of foods high in antioxidant vitamins and decreasing prevalence of either late or early ARM. CONCLUSIONS The authors found no associations between ARM and dietary antioxidants, either from diet alone or including supplements, or from selected foods, in the Blue Mountains Eye Study population.

Effect of omega‐3 fatty acid concentrations in plasma on symptoms of asthma at 18 months of age

The objective of this study was to assess the relation between observed levels of omega‐3 fatty acids in plasma and symptoms of asthma and atopy in children at 18 months of age. A total of 616 women at risk of having a child who would develop asthma because of a family history were recruited from the antenatal clinics of six hospitals in Sydney, Australia. Families were randomized to either active omega‐3 supplemented or control group. The active group received a daily tuna fish oil supplement and omega‐3‐rich margarines and cooking oils and the control group received a placebo supplement with polyunsaturated margarines and cooking oils. When the children were 18 months of age an assessment of symptoms was carried out by a research nurse blinded to treatment group allocation. Atopy was measured by skin prick tests, blood was collected to determine serum immunoglobulin E (IgE), and plasma fatty acid concentrations. A total of 376 children (61.0% of total recruited) completed an assessment at 18 months and had blood taken to determine plasma fatty acid concentrations. Omega‐3 fatty acid levels were expressed in quintiles of exposure ‘as treated’ without reference to treatment group allocation. Wheeze ever, doctor visits for wheeze, bronchodilator use and nocturnal coughing were significantly reduced in children in the higher exposure quintiles. Serum IgE was reduced in the highest quintile but not significantly so. There was no difference in diagnosed asthma or atopy between the exposure quintiles. Although wheeze at this age may not be a good indicator of asthma in later childhood, it is encouraging that some symptoms have been reduced in children with high omega‐3 fatty acid concentrations in plasma.

Consumption of ‘extra’ foods by Australian adults: types, quantities and contribution to energy and nutrient intakes

Objectives:To identify the types and quantities of ‘extra’ foods, or energy-dense, nutrient-poor foods, consumed by Australian adults, and assess their contribution to total energy and nutrient intakes.Subject/Methods:We used 24-h recall data from 10 851 adults, aged 19 years and over, who participated in the nationally representative 1995 National Nutrition Survey. ‘Extra’ foods were defined using principles outlined in the Australian Guide to Healthy Eating and by applying cut points for maximum amounts of fat and sugar within each food category.Results:‘Extra’ foods contributed to 36% of daily energy intake with the highest contributors being fried potatoes (2.8%), margarine (2.6%), cakes and muffins (2.5%), beer (2.4%), sugar-sweetened soft drinks (2.4%), and meat pies (2.2%). Both age and sex were important determinants of ‘extra’ foods intake; younger adults were more likely to consume sugar-sweetened soft drinks, fried potatoes, meat pies and savoury pastries, pizza, crisps, lollies and chocolate; whereas older adults were more likely to consume sweet and savoury biscuits, cakes and muffins, margarine and butter. In all age groups, ‘extra’ foods contributed more to energy intake for men than women. Overall, ‘extra’ foods contributed 16% protein, 41% total fat, 41% saturated fat, 47% sugar and approximately 20% of selected micronutrients to the diet.Conclusions:‘Extra’ foods contribute excessively to the energy, fat and sugar intakes of Australian adults, while providing relatively few micronutrients. This is of concern for the increasing risk of overweight and chronic disease and poor micronutrient status.

Issues in assessing the validity of nutrient data obtained from a food-frequency questionnaire: folate and vitamin B12 examples.

OBJECTIVE To compare methods used to assess the validity of nutrient intake data obtained from a food-frequency questionnaire (FFQ), using folate and vitamin B12 as nutrient examples. DESIGN Cross-sectional sample from a population cohort. SETTING Two postcode areas west of Sydney, Australia. SUBJECTS In total, 2895 people aged 49 years and older provided dietary data using a semi-quantitative FFQ (79% of 3654 subjects examined). The validity of the FFQ was assessed against three 4-day weighed food records (WFRs) completed by 78 people (mean age 70 years). RESULTS Folate and vitamin B12 validity data were assessed using different methods. The Spearman ranked correlations (energy-adjusted) were 0.66 for folate and 0.38 for vitamin B12. Using the Bland-Altman method, following loge transformation, no linear trend existed between the differences and means for folate and vitamin B12. Large differences existed between the FFQ and WFR in individual cases, particularly for vitamin B12. Finally, data were divided into quintile categories for the test and reference method: 79% classified folate within one quintile, 65% classified vitamin B12 within one quintile; there was no gross misclassification for folate and only 3% misclassification for vitamin B12. CONCLUSIONS Different methods of analysis provided different information about the validity of the FFQ. Correlation coefficients should not be used alone to assess the validity of nutrient data, but should be used in conjunction with Bland-Altman analyses. Depending on the use of the data, additional assessment of classification categories is recommended. This worked example demonstrates that absolute intakes of folate and vitamin B12 should be used with caution.