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Assessing dietary calcium intake has become an essential component of studies on osteoporosis. Although some studies (1-4) have assessed the validity of a food frequency questionnaire (FFQ to assess dietary calcium intake in white Americans, we are unaware of any similar studies among Japanese Americans. Therefore, we developed a 35-item FFQ to estimate calcium intake among Japanese and white persons living in Hawaii
METHODS
This validation study was conducted as part of a larger study examining relationships between lifestyle and peak bone mass at the Hawaii Osteoporosis Center, Honolulu. Study participants were women volunteers between the ages of 25 and 34 years, and who were either white or of Japanese ancestry living in Hawaii. For the validation study, 115 participants (36%) (5) from the larger study completed at least five of seven 24-hour diet records; 90 of these 115 participants completed one 35-item FFQ.
The 24-hour diet record forms were sent to participants seven times during 7 months, each time representing a different randomly assigned day of the week. The 35-item FFQ was sent once to each person (n=115) at the end of the 7 months. A short version of the 35-item FFQ (containing 19 food items and surveying the past 7 days) was administered with each 24-hour diet record. Stamped envelopes addressed to the Hawaii Osteoporosis Center were included to encourage response. Instructions, including example responses, were mailed together with the questionnaires. If the questionnaire was not returned within 4 months, telephone contact and/or additional mailings were initiated.
The 35-item FFQ listed 35 calcium-rich food items: 19 foods with at least 25 mg calcium identified by a 1988 food intake study conducted by the Hawaii Expanded Food and Nutrition Education Program (6); 9 food items that came from the subjects' entries in the "other high calcium food" category on the 19-item FFQ (broccoli, spinach, almonds, sardines, soybeans, cottage cheese, shellfish, pudding, and baked beans); and 8 food items chosen from another FFQ designed to estimate calcium intake (eg, milk shakes, cocoa, scalloped potatoes, cream soup or chowder, creamed fish or meats, bread, waffle or pancake, fudgsicle) (3). Opihi (Hawaiian word for limpet), listed on the original 19-item FFQ, was merged in with the category "shellfish" on the new 35-item FFQ. The remaining 18 food...