2.1 Assessment Approach
To guide the approach to assessing dietary supplement use we first identified criteria for it, and then reviewed the literature to select a method that most closely met these criteria. The method selected was then modified and refined so that it more completely met our criteria.
Four basic criteria were identified. The first criterion was that the approach must be appropriate for both in-person and telephone 24-hour dietary recalls, including unscheduled (unannounced) telephone recalls. It was also determined that the recall period for supplement use must be concurrent with the dietary recall period (past day) so that daily nutrient intake estimates from food and supplemental sources combined could be easily calculated. The third criterion was that the approach must be designed for assessing use of all types of dietary supplements including both prescription and non-prescription dietary supplements as well as non-prescription antacids. The fourth and final criterion was that the method selected would have established validity.
After reviewing the literature on approaches to assessing dietary supplement use (Block, Sinha et al. 1994
; Patterson, Kristal et al. 1998
; Patterson, Levy et al. 1999
; Radimer, Subar et al. 2000
; Ishihara, Sobue et al. 2001
; Murphy, Wilkens et al. 2002
; Radimer 2003
; Satia Abouta, Patterson et al. 2003
; Park, Murphy et al. 2006
), it was determined that the supplement inventory methodology best met our criteria. This approach, which is based on a method commonly used in pharmaceutical research to assess use of prescription and over-the-counter medications, has been used for both research (Archer SL 2006
) and surveillance (Radimer, Bindewald et al. 2004
) purposes. Although its validity has not been evaluated with regard to dietary supplement use per se, it has been found to have acceptable validity for assessing medication use (Psaty, Lee et al. 1992
; Sjahid, van der Linden et al. 1998
; Smith, Psaty et al. 1999
; Caskie and Willis 2004
The general structure of the supplement inventory methodology is that participants are asked to bring all of their dietary supplement products to an in-person interview. From the product containers an interviewer records information such as the product name, name of manufacturer, and product form (e.g. tablet, capsule, lozenge). The participant is asked about frequency of use of the product and amount (dosage) taken each time the product is used. In adapting this methodology for use in our software application, which allows for automated collection and coding, we designed a structured approach akin to the multiple pass approach used in the collection of 24-hour dietary recalls. The multiple-pass approach (Wright, Ervin et al. 1994
) is believed to result in more complete and accurate reporting of dietary intake information than other approaches. It involves first, generating a list of all foods consumed during the recall period, reviewing this list, then gathering food product details (e.g. product type, food additions, amount consumed), and lastly, reviewing the information collected to allow the participant to make additions and corrections.
The assessment methodology we have devised, which we describe as a tiered dietary supplement inventory is designed for collection of dietary supplement use information immediately following completion of a 24-hour dietary recall. Tier 1 of the method involves a series of ten questions to screen for use of dietary supplements and non-prescription antacids. Specific product types queried are as follows: multivitamins and multivitamins with minerals; individual vitamins; individual minerals; amino acids; fatty acids; fiber containing supplements; herbals or botanicals; supplements prescribed by a physician; other types of dietary supplements such as glucosamine chondroitin; and non-prescription antacids. If participants report that they used a specific type of product (e.g. report taking a multivitamin or multivitamin with minerals) they are asked to provide the product name, which the interviewer types into a data entry field. Because the sole intent of Tier 1 is to screen for use of dietary supplements and non-prescription antacids, participants may report products in whatever category they wish. For example, it is acceptable for participants to report use of a vitamin C supplement when asked if they took a multivitamin or multivitamin with minerals.
It is expected that more complete and accurate reporting of supplement use will occur by asking about use of specific types of products than by asking a more global question (e.g., asking participants whether they used a dietary supplement on the previous day) because the more detailed questioning may prompt memory. Also, by asking about specific types of dietary supplements we avoid reliance on participants’ conceptualization of “dietary supplements”, which may be incomplete or inaccurate. Of particular concern is the possibility that some participants may narrowly view dietary supplements as only vitamin- and mineral containing products, not realizing that many other products such as fiber supplements and amino acid containing products are also dietary supplements. The screening questions, which encompass all type of dietary supplements, should avoid this potential problem.
If participants report using one or more products in response to the tier 1 screening questions, tier 2 questioning is initiated. Tier 2 requires information to be obtained from product bottles or containers. If the interview is being conducted in-person, the participant is asked to give the interviewer the bottles/containers for the products he/she brought from home. If the interview is being conducted over the telephone, the participant is asked to gather the bottles/containers for all products they reported using the previous day. After the bottles/containers have been collected the following information for each reported supplement is entered in turn: 1) full product name from the label, which allows for identification and selection of a matching product in the dietary supplement database linked with the Module; 2) number of times the product was taken the previous day; and 3) number of tablets/capsules/lozenges/etc. taken each time the product was taken the previous day. There are a number of additional questions that those using the software may opt to have included in tier 2 of the interview. Optional questions include asking about frequency of use over the past 30 days, the reason for use, and place of product purchase.
The third and final data collection step (tier 3) involves reviewing the information collected in tier 2 to allow the participant the opportunity to make corrections or additions.
2.2 Dietary Supplement Database
The National Health and Nutrition Examination Survey (NHANES) Dietary Supplement Database is being used to support the Module (Dwyer, Picciano et al. 2003). This database, which is updated regularly, includes dietary supplements and non-prescription antacids reported by NHANES participants. It includes close to 2,000 products including generic names and strengths for many vitamins and minerals. Also, defaults are available for use in the event that the strength of a product is unknown. The defaults are selected based on the most common strengths reported by NHANES participants. It is a label-based database, meaning that composition information for products (ingredients and amounts) is obtained from product labels.
To accommodate reported products that are not in the database (missing products), the module allows entry of new products. To accommodate their entry, a missing product window appears during the interview. This window includes data entry fields for entering the product name, manufacturer, and contact information for the manufacturer if it is available on the container. Also, ingredients and amounts may be entered. Information for missing products may be entered during the interview or later depending on study specific procedures.
2.3 Demonstration Study
A demonstration study was conducted to test the feasibility of the Dietary Supplement Assessment Module and to assess participant and interviewer satisfaction with it. A total of 99 people (adults and children) who regularly use dietary supplements were recruited through advertisements placed in community newspapers in the Minneapolis-St. Paul Minnesota Metropolitan area. Those who telephoned in their responses to the advertisement were screened for the following study eligibility criteria: 1.) regularly use one or more dietary supplements; and 2.) able to read and speak English. A gift card for a discount store was offered as an incentive for participation.
A single 24-hour dietary recall and tiered dietary supplement inventory were obtained from each participant in the demonstration study. To fully test the interview approach and software, all assessment questions were included (e.g. optional questions such as perceived efficacy, place of product purchase, and use over the past 30 day were included in the assessment).
Approximately one-half of the interviews were conducted in-person (n=48) and one-half over the telephone (n=51) so that the ease of use of the module in both settings could be evaluated. For the in-person interviews participants were mailed instructions that included a listing of the types of products they should bring to the interview. A paper bag labeled with the study name and logo was included to accommodate bringing product containers to the interview. A reminder telephone call was made the day prior to the scheduled interview to remind participants to bring their product containers with them to the interview. The telephone interviews were unscheduled and unannounced and required less preparation.. Participants were simply told that they would receive a phone call at some time over the next few weeks during which they would be asked about their food intake and dietary supplement use.
Evaluation measures included recording the amount of time required to complete the 24-hour dietary recall and supplement inventory portions of the interview. A demographic questionnaire was completed by participants prior to administration of the 24-hour dietary recall and supplement inventory. Immediately after completion of the interview participants were asked to complete a feedback questionnaire that included questions about the supplement inventory portion of the interview. Interviewers were also asked to complete a feedback questionnaire so that their impressions of the supplement inventory questions and process were ascertained. Means and frequencies were calculated to describe the demographic characteristics of the sample and to report results. The correlation between the number of products reported by each participant and the interview length was calculated to evaluate the extent to which this factor influenced interview length.