Validity and Reproducibility of a Self-administered Food Frequency Questionnaire Used in the Baseline Survey of the JPHC Study Cohort I

1Epidemiologic studies of diet and chronic diseases commonly use a food frequency questionnaire (FFQ). A number of studies have examined the validity and the reproducibility of FFQs developed for Japanese populations.- These questionnaires cover a relatively large number of food items, partly reflecting the large variety of food availability and consumption spectrum among the Japanese population. Although shorter questionnaires with fewer food items may be easier to complete and yield a higher response rate, only a few studies have assessed the validity and the reproducibility of brief FFQs for the Japanese population.

2The objectives of this study are to assess the reproducibility and validity of a brief, 44-item food frequency questionnaire used in a baseline survey of the Japan Public Health Center-Based Prospective Study Cohort I. Part of the results have been reported elsewhere.

3Japan Public Health Center-based prospective study on cancer and cardiovascular diseases (JPHC Study)

4The JPHC Cohort I was started in February 1990 when 61,595 men and women aged 40-59 years living in five Public Health Center Districts (Ninohe, Yokote, Saku, Katsushika-kita, and Ishikawa) were asked to complete a self-administered questionnaire including a 44-item food frequency section, which is referred to as the baseline food frequency questionnaire 1 (BFFQ1). Completed questionnaires were collected from 50,245 subjects, with a response rate of 82%.

5The subjects of this validation study were a subsample of the participants in the prospective study in four districts, omitting one area in Tokyo (Katsushika-kita). We selected 122 men and 125 women on a voluntary basis. Table 1 summarizes the sequence of data collection. In three districts of mainland Japan (Ninohe, Yokote and Saku), we obtained 7-day diet records four times in different seasons in 1994, five years after the baseline survey, and administered the same questionnaire (BFFQ2) again in February, 1995. In one district of Okinawa Island, we collected 7-day diet records in the winter and summer of 1995, and the second questionnaire was administered in February 1996. We collected the diet records only twice in this sub-tropical area because the seasonal variations in diet were small. We also collected fasting blood and 24-hour stored urine samples twice, in February and August of 1994 (three mainland districts) or in 1995 (Okinawa district).

6Twenty men and 12 women who failed to provide their complete diet records were excluded, along with 8 men and 6 women who either did not respond or provide complete information for the BFFQ1 or BFFQ2. Subsequently, the remaining 94 men and 107 women were included in this analysis.

7The food frequency questionnaire asked about the usual consumption of 44 food items during the previous month. Standard portions/units were neither specified nor asked. Four frequency categories were employed for the majority of foods (almost never / 1-2 days per week / 3-4 days per week / almost everyday). For rice and bean paste soup, inquiries were made as to the number of bowls consumed per day. Questions on the frequency of alcohol consumption covered six frequency categories (almost never / 1-3 days per month / 1-2 days per week / 3-4 days per week / 5-6 days per week / almost everyday), and queried those who consumed 1-2 days per week or more about the usual combinations and amounts of five beverages (sake, shochu, beer, whiskey, and other) consumed in a day, e.g., one bottle of beer and one bottle of sake. For 9 non-alcoholic beverages, six frequency categories were used (almost never / 1-2 days per week / 3-4 days per week / 1-2 cups per day / 3-4 cups per day / 5 or more cups per day).

8Based on the dietary record data, we developed a food composition table that corresponded to the food items listed in the questionnaire, and determined standard portions/units for each food category using the observed median values. The food composition table was developed and standard portions/units were assigned separately for men and women. Daily nutrient intakes were calculated by multiplying the consumption frequency of each food by the nutrient content of the standard portions/units and summed these values for all foods. Calculation of total energy and 30 nutrients was done with the Standard Food Composition Table and other sources. Consumption of 17 food groups was also determined.

9We collected weighed dietary records over seven consecutive days by a method used in the National Nutrition Survey with some modifications. Research dietitians instructed the subjects to record all foods and beverages prepared and consumed in a specially designed booklet. Participants were asked to provide detailed descriptions of each food, including the method of preparation and recipes whenever possible. The dietitians checked the records at the subjects homes during the survey and reviewed them in a standardized way after completion. The mean daily consumption of nutrients and food groups was calculated.

10To assess the correspondence between DRs and BFFQ2, we compared the mean daily intakes and computed Spearman correlation coefficients for each nutrient and food group. For selected nutrients, we calculated Spearman correlation coefficients between serum and urinary levels (mean of the two measurements) and intakes measured by BFFQ2. To examine the 5-year reproducibility of the questionnaire, we compared the mean daily nutrient intakes and computed Spearman correlation coefficients between BFFQ1 and BFFQ2. The correlation coefficients were energy-adjusted by the residual method.

11Table 2 shows the validity of BFFQ2 for nutrient intakes. The mean daily intakes calculated from BFFQ2 tended to be lower than those computed from DR. For men, energy-adjusted correlation coefficients between BFFQ2 and DR ranged from 0.06 (polyunsaturated fatty acid) through 0.81 (alcohol), with a median of 0.36. For women, it ranged from 0.11 (niacin) through 0.52 (alpha-carotene), with a median of 0.37. The correlations for fatty acids were generally higher when their respective consumption was expressed in terms of the percentage of total fatty acid intake.

12Table 3 shows the validity of BFFQ2 for consumption of food groups. The mean daily intakes calculated from BFFQ2 tended to be lower than those computed from DR. For men, energy-adjusted correlation coefficients between BFFQ2 and DR ranged from 0.08 (seasonings and spices) through 0.75 (alcoholic beverages), with a median of 0.30. For women, it ranged from 0.08 (seasonings and spices) through 0.46 (milk and dairy products), with a median of 0.28.

13Table 4 presents the validity of BFFQ2 for food intakes (g/day) and food frequency (times/day). The validity for food intakes (g/day) and food frequency (times/day) was comparable, although the correlation coefficients were different with the kind of food.

14Table 5 indicates the validity of BFFQ2 using biomarkers of selected nutrients as the reference standard. Among men, dietary intake measured by the questionnaire showed a moderate correlation with serum levels of n-3 polyunsaturated fatty acid, eicosapentaenoic acid, docosahexanoic acid as a percentage of total fatty acid, serum levels of alpha-carotene, beta-carotene, daidzein, genistein, and urinary levels of sodium. Among women, correlations between the questionnaire estimates and biomarkers were generally low.

15Table 6 shows the 5-year reproducibility of the questionnaire for nutrient intakes. The mean daily intakes were generally comparable between BFFQ1 and BFFQ2. For men, energy-adjusted correlation coefficients between BFFQ1 and BFFQ2 ranged from 0.04 (lycopene) through 0.69 (alcohol), with a median of 0.24. For women, it ranged from 0.27 (lycopene) through 0.60 (total fat), with a median of 0.50.

16Table 7 shows the 5-year reproducibility of the questionnaire for consumption of a food group. The mean daily intakes were generally comparable between BFFQ1 and BFFQ2. For men, energy-adjusted correlation coefficients between BFFQ1 and BFFQ2 ranged from 0.15 (algae) through 0.63 (alcoholic beverages), with s median of 0.34. For women, it ranged from 0.18 (algae) through 0.55 (non-alcoholic beverages), with a median of 0.48.

17We found that the mean daily intakes were lower in the questionnaire than in the diet records for most nutrients and food groups. This is probably due to the relatively small number of food items listed in the questionnaire (44 items). Thus, the questionnaire would underestimate the absolute levels of consumption of nutrients and food groups.

18Correlations between the questionnaire and the dietary records were lower than those reported in Western studies, but comparable with those found in Japanese studies.- The results indicate that the questionnaire is reasonably valid in ranking subjects and classifying them into quintiles according to the consumption of many nutrients and food groups.

19Reproducibility of our questionnaire tended to be lower than reported in previous Western and Japanese- studies. We administered the two questionnaires at a 5-year interval, which is substantially longer than the intervals in other studies (typically one year). The longer interval of questionnaire administration would result in the observed lower correlations. The reproducibility of the questionnaire in the present study was generally higher in women than in men, suggesting that patterns of nutrient and food consumption are more stable over time in women than in men among the Japanese population.

20In conclusion, this brief, 44-item food frequency questionnaire used in the baseline survey of the Japan Public Health Center-Based Prospective Study Cohort I provides reasonably useful measures of intake for many nutrients and food groups. The questionnaire would be useful in examining the association between diet and health in the Japanese population.