• Component Description
• Eligible Sample
• Interview Setting and Mode of Administration
• Quality Assurance & Quality Control
• Data Processing and Editing
• Analytic Notes
• Codebook
  • SEQN - Respondent sequence number
  • DSDSUPID - Supplement ID number
  • DSDSUPP - Supplement name
  • DSD070 - Was container seen?
  • DSDMTCH - Matching code
  • DSD090 - How long supplement taken (days)?
  • DSD103 - Days supplement taken, past 30 days
  • DSD122Q - Quantity of supplement taken daily
  • DSD122U - Dosage form
  • DSDANTA - Antacid reported as a dietary supplement
• Appendix 1: Handcard DSQ1
• Appendix 2: Vitamins/Minerals on the “Strength Only” List
• Appendix 3: Created Default Supplements and Antacids
• Appendix 4: Data File Structure and Relationship

National Health and Nutrition Examination Survey

2005-2006 Data Documentation, Codebook, and Frequencies

Dietary Supplement Use 30-Day - File 2, Participant's Use of Supplements (DSQ2_D)

Data File: DSQ2_D.xpt

First Published: October 2008

Last Revised: July 2009

Component Description

The Dietary Supplements section (DSQ) provides personal interview data on use of vitamins, minerals, herbals and other dietary supplements. This section also includes information on the supplement reported such as supplement name, ingredients, amounts, and serving size.

Eligible Sample

All survey participants are eligible for the dietary supplement questions.

Interview Setting and Mode of Administration

The Dietary Supplement questionnaire was done before the physical examination, in the home, using the Computer-Assisted Personal Interviewing-CAPI (interviewer-administered) system. Persons 16 years of age and older and emancipated minors were interviewed directly. A proxy provided information for survey participants who were under 16 years of age and for individuals who could not answer the questions themselves.

The Interviewer Procedure Manuals and Survey Questionnaires can be found on the NHANES website.

Quality Assurance & Quality Control

Data were routinely examined for discrepancies and erroneous entries.  Trained nutritionists reviewed incoming data and matched reported supplements to known supplements from the NHANES database, where possible; sought additional supplement labels if feasible; assigned generic or default supplements as appropriate; transferred or removed inappropriate products; and assigned matching codes (confidence codes).

 

Data Processing and Editing

Data Collection Methods
During the household interview, survey participants are asked if they have taken a vitamin, mineral, herbal or any other dietary supplement in the past 30 days. Participants are shown a hand card that lists examples of dietary supplements (Appendix 1: Hand card DSQ1). Those who answer “yes” are asked to show the interviewer the dietary supplement containers of all the products used. For dietary supplements listed in Appendix 2: Vitamins/Minerals on the “Strength Only” List, only the strength is recorded. For all other dietary supplements reported, the interviewer enters the product’s complete name from the container into a computer. If the container is not available, the interviewer asks the participant to verbally report the name of the dietary supplement. The interviewer then tries to find the supplement on a list created by NCHS. If an exact match of the dietary supplement cannot be found, the interviewer is instructed to select “product not on list” from the list. Interviewers can record up to 20 dietary supplements. The manufacturer is either selected from the manufacturer list or entered manually. The same process is also repeated for non-prescription antacids.

Participants are asked how long they have been taking the dietary supplement, how many times in the past 30 days they have taken it and how much do they take on the days they took the supplement.

The NHANES 2005-2006 dietary supplement questions can be accessed in the Dietary Supplements and Prescription Medications Section of the Sample Person Questionnaire.

Dietary Supplement Questions Included in this Data Release

• Was any dietary supplement taken in the past 30 days
• Number of dietary supplement(s) taken
• Dietary supplement name
• Was dietary supplement container seen by interviewer
• How long was supplement taken
• Number of days supplement taken in the past 30 days
• Quantity of dietary supplement taken daily
• Was any non-prescription calcium/magnesium-containing antacids taken in the past 30 days
• Number of non-prescription calcium/magnesium-containing antacids taken
• Information from the dietary supplement label, such as ingredients, amounts, serving size.

Matching reported supplements to products in the database and obtaining product labels

Matching reported dietary supplements to known products
Trained nutritionists, at NCHS, match the product names entered or selected by the interviewer (including prescription supplements and antacids containing calcium or magnesium) to a known dietary supplement product when possible. These matches are made with varying degrees of precision, and a matching code (DSDMTCH) accompanies each match. The matches are: 1) Exact or near exact match; 2) Probable match; 3) Generic match; 4) Reasonable match; and 5) Default match. In some cases no match can be made with any certainty. These products are coded 6) No match. Products whose names were reported as “Refused” (7777) or “Don’t know” (9999) have matching codes of 7 and 9, respectively. NCHS nutritionists first determine if the product is in our database. If it is, then nutritionist look at the date that the product label was entered to make sure it was entered within the cycle of data collection, which is a 2 year cycle. If the product label is not entered into the database, or the product label is old, NCHS nutritionist attempt to obtain a new product label.

NCHS attempts to obtain a label for each supplement reported by a participant from sources such as the manufacturer, distributor or retailer, the Internet, company catalogs, and the Physician’s Desk Reference (PDR).

NCHS communicates with many major manufacturing company representatives to determine when various product re-formulations become available. Based upon manufacturer advice, we have used a lag time of 5 months after the new re-formulated product has hit the market. Despite these precautions, there is no guarantee that the product taken by respondents is the correct formulation.

NCHS created generic and default dietary supplements and entered these into the supplement database. Reported supplements for which the strength of all ingredients was known were matched to a generic supplement, i.e. one which had no brand name. These were generally single ingredient supplements which included a strength (e.g. vitamin C 500 mg) or multiple vitamins and/or mineral supplements made by a private label manufacturer that was known to us and for which we had a label with identical ingredients and strengths (e.g. brand X all-purpose multivitamin was reported, and we had a label for brand Y, made by the same manufacturer). These matches are coded as 3 (DSDMTCH=3).

When all ingredient strengths were not known, the supplement was matched to a default supplement where possible. Defaults were created for single ingredient and multiple ingredient supplements based on our own data of most frequently reported supplements of that type. These matches were coded as 5 (DSDMTCH=5). Created default products and the actual products or strengths that were assigned to these defaults are listed in Appendix 3 (Created default supplements and antacids).

The NCHS Dietary Supplements Database
NCHS maintains a dietary supplement database. This is not a comprehensive dietary supplements database and only contains dietary supplements and calcium and/or magnesium-containing antacids that have been reported in the NHANES survey since 1999. The ingredient information entered into the database is taken directly from the supplement facts box on the label or carton, if available, or the equivalent from other sources. NCHS nutritionist enter from the label: supplement name; manufacturer; serving size; form of serving size; ingredients and amounts, including an operator to indicate that the amount is less than, more than or equal to the amount.

NCHS does not verify the actual composition of supplements reported: the database is based on label information, not testing. The best information source is the label itself, but when this cannot be obtained, other sources are used. Information from other sources may not always be an accurate reflection of what is actually on the supplement label. This is true for the supplement’s apparent name as well as for the ingredients. The apparent name on the container is most important, since interviewers see the supplement container and record the name as it appears to them. Differences from what appears on the label are particularly noted for information from the Internet (name and ingredients), the PDR (name), and supplement carton (name). In addition, supplements may change the appearance of a label and thus the apparent name without changing the content or may change content with minimal change to the label, or may change both. NCHS attempts to obtain updated labels as they come onto the market, but cannot guarantee complete success. The source of the supplement information (DSDSRCE) is included in the data release.

Ingredients may be listed in various ways, for example: in their elemental form (e.g. calcium); as compounds (e.g. calcium citrate); as plant forms (e.g. extract, concentrate, oil) or plant parts (e.g. root, leaf); as percentages (e.g. beta carotene- % of vitamin A); and as blends or complexes (e.g. bioflavonoid complex; proprietary blend). Suggestions for conversion of compounds are contained in Dietary Supplement Database documentation. These are based upon literature searches, but may contain errors. Users should verify these conversions. Note especially that there are a number of conversions for ferrous sulfate depending upon its form, which was not always specified.

Some supplements contain proprietary blends of ingredients, generally non-nutrients. An amount is specified for the blend but not individual ingredients in the blend. In such cases, the blend and its amount are entered into the database, but the individual ingredients of the blend are listed without any amounts. A few supplement labels list ingredients but no amounts at all, so the amounts are missing.

Product information is released from the in-house Dietary Supplement Database as the NHANES Dietary Supplement Database (NHANES-DSD) which contains detailed information on the dietary supplements and antacids reported by survey participants since NHANES 1999. The NHANES-DSD release consists of three datasets which contain information on products:

Dietary Supplement Product Information (DSPI)
Dietary Supplement Ingredient Information (DSII)
Dietary Supplement Blend Information (DSBI)

The supplement ID numbers (DSDSUPID) located in the Individual Dietary Supplements File can be used to merge with the NHANES-DSD files. For more information on the NHANES-DSD, please refer to the documentation and release files located on the NHANES website.

Data Editing

When a variable was modified globally, as part of the editing process, the third letter in the variable name was changed from a Q (i.e. DSQ) to a D (i.e. DSD).  Variables that were obtained or generated from an external database (i.e. dietary supplement database) will also have the letter “D” in the third position of the variable name.

Dietary supplements incorrectly reported in subsections of questionnaire:

Prescription and non-prescription dietary supplements that were incorrectly reported in the nonprescription antacid section of the questionnaire were removed from the nonprescription antacid file and added to the dietary supplement file. All non-prescription antacids that contained calcium and/or magnesium were moved to the dietary supplement file.

Prescription supplements are released in the Dietary Supplements Data File. Some prescription medications were mistakenly recorded in the dietary supplement section. These were removed and added to the prescription medication file. Any prescription dietary supplement that was incorrectly reported in the prescription medication section was removed from the prescription medication section and moved to the dietary supplement section. Strength and details of the persons’ usage are missing for these supplements, because these questions are not asked in the prescription medication questionnaire. The following products were moved to the dietary supplements files from the prescription medication file:

• All calcium products except calcium acetate
• All fluoride products except those in topical gel or cream forms (e.g., stannous fluoride) 
• Over-the-counter niacin, niacinamide, and nicotinic acid.

All prescription niacin, potassium, and sodium products were retained in the prescription medication file.

Specific variables and edits:

DSD010: Have you used or taken any vitamins, minerals or other dietary supplements in the past 30 days? Include prescription and non-prescription supplements.

This variable was the lead-in question to the series of questions on dietary supplement use. This variable was edited and takes into account dietary supplements reported in this section as well as dietary supplements moved in from the prescription medication or nonprescription antacid sections of the questionnaire.
A small number of persons refused to answer this question (coded 7) or did not know whether they used a dietary supplement in the past month (coded 9).

DSDCOUNT: The number of dietary supplements taken
This variable was computed at NCHS and represents the total number of dietary supplements reported by the respondent including those dietary supplements identified as unknown (DSDSUPID = 666XXXXX). The count has been adjusted for all dietary supplements moved into and those moved out of the dietary supplements section. Antacids that were reported in the dietary supplement section were assumed to be taken as a supplement and also included in the count (DSDANTA=1). Antacids reported in the non-prescription antacid section or the prescription medication section do not contribute to this count (DSDANTA=2). There were also participants who reported the use of a dietary supplement in the past 30 days (DSD010 = 1) but did not know the name of the dietary supplement (DSDSUPID = 99999) or refused to report the name of the dietary supplement (DSDSUPID = 77777). Each product reported as refused or don’t know is still included in the total count of dietary supplements used under DSDCOUNT.

DSD010AN: Any non-prescription antacids taken?
This variable was created at NCHS to indicate whether or not non-prescription calcium and/or magnesium antacids were reported in other sub-sections of the questionnaire. This variable only takes into account these types of antacids reported in the non-prescription antacid section or the prescription medication section. There were a few non-prescription calcium/magnesium-containing antacids reported in the dietary supplement section and these were included in DSD010 and DSDCOUNT.

DSDANCNT: The number of non-prescription calcium and/or magnesium - containing antacids taken.
This variable was computed at NCHS and represents the total number of non-prescription calcium and/or magnesium containing antacids reported by the respondent. Only antacids reported in the non-prescription antacid section or the prescription medication section contribute to this count (DSDANTA=2). Antacids that were reported in the dietary supplement section were assumed to be taken as a supplement and included in the dietary supplement count (DSDANTA=1).

DSDANTA: Created variable that indicates whether an antacid was reported in the dietary supplements section or the Antacid section of the questionnaire.
Information on use of non-prescription antacids was sometimes recorded in the dietary supplement section; other times in the antacid sub-section of the medication section. Due to their nutrient content, antacids that contain calcium or magnesium are released with the dietary supplement data, irrespective of where they were reported. Only these antacids are reported; this is not a complete accounting of all antacids. Thus, users are cautioned that analyses of these data to estimate the percentage of antacids used as dietary supplements would not be appropriate.  For a few participants, the same antacid was recorded in both questionnaire sections. In these instances, the antacid was considered to be in the DSQ section and coded as 1.

DSDMTCH: matching code confidence codes
Supplements are recorded in the household interview with varying degrees of accuracy and completeness. NCHS has created a system to specify how certain we are with matching a supplement recorded during the interview with the actual supplement label. Analysts should be aware that for default matches and matches that chose between several similarly named supplements, there is less certainty that the ingredients and ingredient amounts in the supplement assigned exactly match those in the supplement actually taken. Additionally, NCHS cannot guarantee in any case that the matched product was the exact product taken or even that any product actually was taken, as these data are self-reported.

DSD070: Dietary supplement container seen by interviewer?
This variable indicates whether the dietary supplement container was seen. Containers are seen approximately 88% of the time. A more precise name for a supplement can be recorded by the interviewer, and thus a more precise match to a known supplement can be made, when the interviewer sees the supplement container rather than recording the participant’s report of the supplement name (for example, multivitamin/multiminerals are often reported as multivitamins). In general, this is reflected in the matching code, but analysts should be aware that precision is greater when a container is seen.

This variable is mostly unedited. Interviewers ask to see the containers in all three subsections of the Dietary Supplements and Prescription Medications Section. Therefore, any dietary supplements moved into the dietary supplement file will contain this information. In 2005-2006, this indicator was accidentally left off the non-prescription antacid questionnaire. For these records, DSD070 will be missing.

DSD090: For how long have you been taking this product or a similar type of product?
This variable was created from a two-part (number and unit) question and indicates how long the respondent reported taking each dietary supplement. The data from variables: DSQ096Q/U (dietary supplement section), RXQ180Q/U (non-prescription antacid section and RXQ260Q/U  (prescription medication section) were combined. Responses were recorded in days, weeks, months, and years. To facilitate analysis, all answers were converted to days using conversion factors of 7 days per week, 30.4 days per month, and 365 days per year. There were persons who reported the use of a dietary supplement but did not know how long they had been using the product (DSD090 = 99999) or refused to report the length of use (DSD090 = 77777). There were also persons who reported the use of a dietary supplement but did not report the length of use. DSD090 is missing for these persons.

DSD103: In the past 30 days, on how many days did you take the product?
This variable is mostly unedited. It combines data from two variables: DSQ103 (dietary supplement section) and RXQ191 (non-prescription antacid section). This information is missing for dietary supplement data that was recorded in the prescription medication section, since this question is not asked in this sub-section.

DSD122Q/U: On the days that you took the product how much did you} usually take on a single day?
These two variables are mostly unedited. They do contain data which combined variables: DSQ122Q and DSQ122U (dietary supplements section) and RXQ214Q and RXQ214U (non-prescription antacid section). This information is missing for dietary supplement data that was recorded in the prescription medication section, since this question is not asked in this sub-section.
The data was edited to take into account label serving size. For example, if a respondent reported taking 1 tablespoon of a supplement and the label serving size was 3 teaspoons, than the variable was edited to 3 teaspoons (1 tablespoon = 3 teaspoons).
In some cases the reported serving size is in different units than the label serving size. For example, the respondent may have reported 1 tablet, but the label serving size is 1 tablespoon. This was assumed to be an error in reporting or an interviewer error in data collection. In these cases the serving size was assumed to be the label serving size. There were 86 records in which this occurred and the data was edited to the label serving size. All records that were assigned a default product were edited and the default serving size was assumed.

Analytic Notes

The 2-year sample weights (WTINT2YR, WTMEC2YR) should be used for NHANES 2005-2006 and 2003-2004 analyses. There are no 4-year weights in these files. The 4-year weights were provided with the NHANES 2001–2002 release file because there were some transition issues related to the use of 1990 Census and 2000 Census information. Detailed instructions for linking earlier datasets (1999–2000 and 2001–2002) are provided in the NHANES Analytic Guidelines.

Since this data is collected during the household questionnaire, interview weights should be used. Although these data were collected as part of the household questionnaire, if they are merged with the MEC exam data, exam sample weights should be used for the analyses. Please refer to the Analytic Guidelines for further details on the use of sample weights and other analytic issues. The Analytic Guidelines are available on the NHANES website.

Using self-reported data
NHANES data are self-reported and recorded by interviewers, and thus may contain inconsistencies or errors. Some inconsistencies were edited, however, users may notice situations that still need editing. Users are advised to assess the data and edit it as deemed appropriate for the analyses being undertaken.

Use of format libraries
The text labels for supplements, ingredients, units, etc. are provided in a separate data file called “Supplement Format File (DSQFMT)” in order to keep the data files a reasonable length. SAS code to link the Supplement Format File with the data files or to obtain a list of formatted text labels is provided in the documentation. A list of the supplement and ingredient ID numbers and names can be made by running a proc freq of these variables and using the format library to link the name to the ID number.

Deriving nutrient estimates from dietary supplement data
Dietary supplement and antacid intake data (DSQ) refer to the past 30 days. The data necessary for computation of total nutrient intake are:
personal usage data (DSQ files 1& 2); dietary supplement composition data (DSQ files DSPI, DSII, DSBI).

The analyst must combine these files: File 1 portrays a participant’s overall use of supplements; file 2 refers to the person’s usage of one particular supplement; and files DSPI, DSII, and DSBI refer to the content of one specific supplement.

DSQ codebooks, documentation, and data are described in the questionnaire section of this data release.

Dietary supplement data were reported as times per month in 1999-2000 and days in the past month in 2001-2002, and days in the past 30 days in 2003-2006. For participants who took one supplement each day, one time per day, daily nutrient intake from supplements can be estimated directly from the label ingredients.

Intake of multiple supplements with the same nutrient(s), multiple use of the same supplement on the same day, and nutrients in blends must be taken into account in nutrient calculations. Nutrient names and the quantity units need to be synchronized and nutrient amounts from all these calculations must then be summed. Some nutrient amounts are for a nutrient compound (generally a foreign-made product or an antacid) and these must be converted to a nutrient amount.   If one or more supplements were taken less than daily, estimation of supplement nutrient intake could be calculated for a month, a daily average, highest possible daily intake, or lowest non-zero intake.

See analytic notes above and Appendix 4 for information on how to link the files containing the person, supplement, and ingredient variables.

Combining nutrient estimates from dietary supplement plus food- recall data
To estimate total dietary nutrient intake, nutrients from diet, supplements, and antacids should be combined. Because of different data collection, referent time periods, and release systems, these data require some manipulation and assumptions to combine. Consequently, the resultant total may not provide a very accurate estimate of daily total nutrient intake nor is a variance estimate directly available. This would need to be calculated using special programs developed for this purpose (e.g. C-Side).

Deriving nutrient quantity from dietary supplement requires extracting the nutrient content of each supplement, as described above. Dietary recall data (DRX) are released as total combined nutrient amount from all foods reported on the one day dietary recall; no derivation is needed (e.g. calcium quantities from all food sources are combined and released as a single one day quantity). RXQ codebooks, documentation, and data are located in the exam section of the data release.

Because of the different time referents for dietary supplement and food intake, an analyst must decide upon the most useful way to combine these data to estimate intake for a given purpose. For example, if supplement use was reported to be daily, the nutrient value from the supplement could be simply added to the recall nutrient value, although the time frames do not overlap. When some or all supplements were taken less than daily (1999-2000) or less than 30 times a month (2001-2006), the nature of the analysis and the data itself should guide the decision about nutrient calculation.

For instance, if a supplement were taken nearly monthly, an analyst could:
1) assume intake to be daily;
2) calculate monthly intake based on intake frequency;
3) calculate average daily value from the monthly value; or
4) analyze data only from people who took supplements daily

The latter would mean that the sample would no longer be representative of all supplement users, but should represent daily supplement users.

Because of the data differences, combining nutrient intake from these different variables to estimate total nutrient intake requires thoughtful consideration of the analytic goal and methods, and deserves accurate description of methods, assumptions, and weaknesses in any presentation of results.

Codebook and Frequencies