National Health and Nutrition Examination Survey

The Dietary Supplement and Prescription Medication Section (DSQ) of the Sample Person (SP) Questionnaire, collects information on 1) prescription and non-prescription dietary supplements (DS), 2) non-prescription antacids, 3) prescription medications, and 4) asthma medication.

The dietary supplement sub-section collects personal interview data on use of DS during a 30 day period prior to the survey date. The NHANES 2011-2012 dietary supplement questions are similar to the NHANES 1999–2010 and NHANES III 1988–1994 questions, although, there have been additional questions added over the cycles.  Analysts are encouraged to read the documentation in order to understand the names and structure of the files as well as the variables.

Non-prescription antacids which contained calcium and/or magnesium (antacids) are also included in these data files.

The DS reported in the NHANES 2011-2012 are detailed in the NHANES Dietary Supplement Database (NHANES-DSD) 1999-2012. The NHANES-DSD contains detailed information on the DS and non-prescription antacids containing calcium and/or magnesium (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), and Dietary Supplement Blend Information (DSBI).

30-Day Dietary Supplements Data Files: Two data files were produced from the 30-day dietary supplement and non-prescription antacid sub-sections of the DSQ interview: Total Dietary Supplements file and Individual Dietary Supplements file.

Individual Dietary Supplements File (DSQIDS_G): Contains detailed information about the types and amounts of individual DS and antacids reported by each participant. The names for the variables included in this file are listed in Appendix 1.

The Individual Dietary Supplements File includes one record for each dietary supplement or antacid consumed by a survey participant. Only participants’ that had reported taking a dietary supplement or an antacid are included in these files. Each dietary supplement or antacid is identified by a supplement ID number (DSDSUPID) and each record contains, but is not limited to, the information listed below:

• Name and ID number of the supplement
• Reason(s) for using the supplement
• Amount of dietary supplement consumed in serving size, which is calculated as the reported amount consumed divided by the serving size from the product label 
• Amounts of 34 nutrients/dietary components (listed in Appendix 2) from each dietary supplement and antacid, as calculated using the NHANES-DSD.  If data is missing for any of the variables needed to calculate the amounts consumed for the selected nutrients, this information will be missing for individuals, even though they reported a supplement (s).

This file only includes intake for a select group of nutrients. These records can be linked to the NHANES-DSD, using supplement ID numbers (DSDSUPID), to obtain more detailed information on reported products. The NHANES-DSD datasets provide information on nutrients in the dietary supplement as reported on the product label. Botanical ingredients would be an example of nutrients not released in the Individual Dietary Supplements files, but can be obtained from the NHANES-DSD files.

Total Dietary Supplements Files (DSQTOT_G): Contains, for each participant, daily total nutrient intakes from DS and antacids. The names for the variables are listed in Appendix 3.

The Total Dietary Supplement File provides a summary record of total nutrient intakes from DS and antacids for each individual. All participants in the Household sample are included in this file. This includes users and non-users of DS and antacids. Each total intake record contains, but is not limited to, the following information: 

• Whether a dietary supplement or an antacid was consumed in the past 30 days 
• Total number of supplements and antacids reported for that participant 
• Mean daily intake aggregates of 34 nutrients/dietary components (listed in Appendix 2) from all supplements and antacids, as calculated using the NHANES-DSD.   If data is missing for any of the variables needed to calculate mean daily intakes, this information will be missing for individuals, even though they may have reported a supplement (s).

All survey participants are eligible for the DSQ questionnaire.

The DSQ was asked by trained interviewers before the physical examination, in the home, using the Computer-Assisted Personal Interviewing (CAPI) system. Participants over 16 years of age answered for themselves. 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 Survey Questionnaires can be found on the NHANES website.

Data were routinely examined for discrepancies and erroneous entries. Trained nutritionists reviewed incoming data and matched reported dietary supplement entries to known supplements from the in-house NCHS Product Label Database (PLD), where possible; sought additional product labels if feasible; assigned generic or default supplements as appropriate; transferred or removed products that were not considered DS (i.e. prescription medication); and assigned matching codes (confidence codes). All coding was reviewed by the project officer.

Data Collection Methods

Dietary Supplements

During the household interview survey participants are asked if they have taken a dietary supplement in the past 30 days. Participants are shown a hand card that lists examples of DS (Appendix 4). Those who answer “yes” are asked to show the interviewer the dietary supplement containers of all the products used. For DS listed on the “Strength Only” List, only the nutrient is selected and the strength(s) are recorded (see Appendix 5). For all other DS reported, the interviewer enters the product’s complete name from the container into a computer. The interviewer enters the name a second time as verification. Interviewers can record up to 20 DS. If the container(s) are not available, the interviewer asks the participant to verbally report the name of the dietary supplement. The manufacturer is either selected from the manufacturer list or entered manually.

Non-prescription antacids

During the household interview survey participants are asked if they have taken non-prescription antacids in the past 30 days. Those who answer “yes” are asked to show the interviewer the containers of all the products used. For each antacid reported, the interviewer enters the product’s complete name from the container into a computer. If the containers are not available, the interviewer asks the participant to verbally report the name of the antacid.

When the interviewer enters the antacids name into the computer, the name is automatically matched to a prescription drug database (which also contains non-prescription antacid products) on the computer to identify an exact match or similar text matches. The interviewer then selects the best match from a list of possible matches. The original entry of the interviewer and the product selected from the computer list are saved under separate variables for quality control purposes. If an exact match of the product cannot be found, the interviewer is instructed to select “drug not found on list” from the list. Interviewers can record up to 20 non-prescription antacids. Nutritionist at NCHS then process the data collected to determine which products contain calcium and/or magnesium. The non-prescription antacids that contain calcium and/or magnesium are released with the dietary supplement data files.

Participants are also asked how long they had been taking the each dietary supplement or non-prescription antacid reported, how many days it was taken in the past 30 days, the amount that was taken on those days and the reason(s) that they are taking the dietary supplement or non-prescription antacid.

The NHANES 2011-2012 dietary supplement questions can be accessed in the Dietary Supplement and Prescription Medication Section (DSQ) of the Sample Person (SP) Questionnaire.

Matching reported dietary supplements to known products

Trained nutritionists, at NCHS, match the product names entered by the interviewer (including prescription supplement, non-prescription supplement and antacids) to a known product when possible. NCHS nutritionists first determine if the product is in our in-house PLD. If it is, then the nutritionist verifies whether the product label was entered into the system within the 2-year cycle of data collection. If the product label has not been entered into PLD, or the product label was entered before the beginning of the 2-year data collection cycle, NCHS nutritionist attempt to obtain a new product label. NCHS obtains labels for each dietary supplement or non-prescription antacid containing calcium and/or magnesium reported by participants’ 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 hit the market and matched products to participants’ accordingly. Despite these precautions, there is no guarantee that the product taken by participants’ is matched to the correct formulation in our release files.

NCHS nutritionist attempt to find the exact product(s) reported by participants’; however, this is done with varying degrees of precision. A “matching code or confidence code” (DSDMTCH located in file DSQIDS_G) accompanies each record to indicate the degree of matching certainty. The matches are: 1) Exact or near exact match; 2) Probable match; 3) Generic match; 4) Reasonable match; or 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” (DSDSUPP=7777) or “Don’t know” (DSDSUPP=9999) have matching codes (DSDMTCH) of 7 and 9, respectively.

NCHS created generic and default DS and antacids, which are also maintained in the database. Generics are created in the database and used when we have collected information about a reported supplement such as strength of all ingredients, but 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). When all ingredient strengths were not known, a default supplement in the database was used to code the reported supplement. Defaults were created for single ingredient and multiple ingredient supplements based on our own data of most frequently reported supplements of that type, based on the survey cycle in which the data was collected. Created default and generic products and the actual products or strengths that were assigned to these defaults are listed in Appendix 3.

After the dietary supplement data is coded and matched to a product in our in-house database, various types of reviews were conducted to ensure the quality of the data. Interviewers' comments are reviewed to ensure that they have been accounted for in coding. Decisions are made about how to code new or unusual dietary supplement products or unusual quantities or units reported by survey participants. Dietary supplements that could not be matched to items in the database are resolved by NCHS nutritionist.

Product information is released from the in-house PLD as the NHANES-DSD which contains detailed information on the DS 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 dietary website.

Data Editing

Non-prescription antacids containing calcium and/or magnesium that were reported in the non-prescription antacid section of the questionnaire are included in the present dietary supplement files.

Prescription medications, including prescription antacids are released in the Prescription Medication Data File.

The following prescription products are included in the dietary supplement files: 

• 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 vitamin D products, with the exception of 2 records for Paricalcitol (D2) that were retained in the 2011-2012 prescription medication data file
  
  

All prescription niacin, potassium, and sodium products were retained in the prescription medication file. Combination products that include prescription drug (s) and dietary supplement ingredients are retained in the prescription medication file (e.g. combination drug alendronate with cholicalciferol  or Fosamax with vitamin D3).

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.

Participants with a record of having taken a product determined to be a dietary supplement in the last 30 days are coded 1. This variable was edited and takes into account DS reported in any of the sub-sections of the DSQ. Some products were mistakenly recorded in the prescription medication sub-section. These data have been moved to the dietary supplement files and are counted as supplements for DSD010 and DSDCOUNT. Participants who took their antacid containing calcium or magnesium as a dietary supplement and reported them in the dietary supplement sub-section are also coded 1. Participants who reported taking an antacid containing calcium or magnesium in the last 30 days that was recorded only in the non-prescription antacid sub-section, but did not take any dietary supplement are coded 2. Participants who did not take any product that was determined to be a dietary supplement in the last 30 days are also coded 2, even if they originally reported having taken a supplement. Examples of products that were determined not to be supplements included foods (garlic cloves, raisin bran cereal, PowerBar®), drinks (Ensure®, Gatorade®, tea), over the counter drugs (aspirin, laxatives, electrolyte replacement fluids), homeopathic medicines, and prescription medicines. Prescription medicines were moved from the dietary supplement files to the appropriate prescription medication files. A small number of persons refused to answer this question (coded 7) or did not know whether they used a dietary supplement in the 30 days (coded 9).

DSDCOUNT: The number of DS taken

This variable was computed at NCHS and represents the total number of DS reported by the respondent including those DS identified as unknown (DSDSUPID = 6666666XXX). Antacids that were reported in the dietary supplement sub-section were assumed to be taken as a dietary supplement and also included in the count. Antacids reported in the non-prescription antacid or the prescription medication sub-sections of the DSQ questionnaire do not contribute to this count. There were also participants who reported the use of a dietary supplement in the past 30 days but did not know the name of the dietary supplement (DSDSUPP = 99999) or refused to report the name of the dietary supplement (DSDSUPP = 77777). Each product reported as refused or don’t know is still included in the total count of DS.

DSD010AN: Any non-prescription antacids taken?

This variable was created at NCHS to indicate whether or not an antacid was reported. This variable only takes into account these types of antacids reported in the non-prescription antacid sub-section of the DSQ questionnaire. In previous data releases, there were a few antacids reported in the dietary supplement sub-section of the DSQ questionnaire and these were considered to be taken as DS and included in the DSD010 and DSDCOUNT. There were no antacids reported in the dietary supplement sub-section in 2011-2012.

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 antacids reported by the participant. Only these antacids reported in the non-prescription antacid sub-section of the DSQ questionnaire contribute to this count. Antacids that were reported in the dietary supplement sub-section were assumed to be taken as a supplement and included in the dietary supplement count.

DSDANTA: Created variable that indicates whether an antacid was reported in the DS sub-section or the non-prescription antacid sub-section of the DSQ questionnaire.

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

DSDSUPID: Supplement ID Number

Supplement ID is a 10 digit identifier assigned to each product entered into the PLD. All identifiable products have a supplement ID beginning with the number “1.” The next 3 digits (positions 2-4) are: “888” or “881” if the supplement was created by NCHS as a generic or default product; otherwise the digits in positions 2-4 are coded “000” or “001.” The next 4 digits (positions 5-8) are sequentially assigned by the system for each product. The last 2 digits (positions 9-10) indicate formulations of the same supplement: the first formulation entered into the database = 00, the first re-formulation = 01, the next = 02, etc. Note that these are reformulations of the same product. Different versions of products (e.g., liquid vs. tablet, with iron vs. without iron, regular vs. high potency) are considered as different products and have different 4 digit numbers in positions 5 to 8. When a product name was entered as "no product information available," “refused,” or “don’t know,” its ID number starts with a string of 6’s.

DSDSUPP: Name of Supplement

This is the name from the front of the product label. The brand name is generally entered first (i.e., Nature’s Way) and then the actual product name (i.e., lutein). Information such as the strength (i.e., 60 mg extract) of the product and other qualifiers that help distinguish a product from a similar product (i.e., mega, super, high potency, time release, chewable, extract) are also listed if they are on the front of the product label. Words like “dietary supplement” and health claims are not entered as part of the name.

DSDMTCH: matching code confidence codes

Supplements are recorded during the DSQ of the questionnaire 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 product label.

Below describes how matches are made.

Exact or near exact match (DSDMTCH=1) indicates that this is the only product that could match this entry.

Probable match (DSDMTCH=2) indicates that the match is not exact, but knowledge of the company’s products strongly suggests that this is the only possible match choice. For example the entry may not specify strength or include words such as timed release, but no other options are available for this brand according to manufacturer or retailer information.

Generic match (DSDMTCH=3) indicates we had information on the strength for all ingredients, either a) as part of name (e.g., vitamin C 500 mg) or b) because the manufacturer is known and NCHS has an identical product made by this manufacturer for a different distributor or retailer. Thus the ingredients and amounts are considered to be accurate despite an exact brand match.

Reasonable match (DSDMTCH=4) indicates that the product name may be incomplete or could be complete but other products of this brand also start with these same words so this cannot be assured. In these cases, the entered name is matched to either: a) the most frequently reported of these products in the NHANES 2011-2012 data, if this could be determined; b) the best-selling product by this company that matches the entered name; or c) the most basic product by this company, as assessed by label wording.

Default match (DSDMTCH=5) indicates that the exact product could not be obtained because the name was imprecise or the exact brand product could not be located and no generic could be assigned. In these cases, the entered product was matched to a created default product based upon: a) the most commonly reported strengths for single ingredients; b) the most commonly reported brands for major multiple ingredient products such as multivitamins and multivitamin/multiminerals for children, seniors, or adults, if available; or c) products manufactured by a large, private-label manufacturer.

Finally, a match codes of No match (DSDMTCH=6) indicates that no product could be found and there was not enough detail in the name to assign a generic or default match with any confidence. The words “no product information available” are listed as the product name (DSDSUPP).

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 product container was seen by the interviewer. Containers were seen for approximately 80% of the records. 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 sub-sections of the DSQ questionnaire. Therefore, most records included in the dietary supplement file will contain this information.

DSD090: For how long have you been taking this product or a similar type of product?

This information was collected using two-part (number and unit) questions to allow participants to report how long they had been taking the product or similar product in days, weeks, months, or years. The released variables were edited to standardize the reported length of time to number of days, using the following conversion factors: 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 or antacid but did not know how long they had been using the product (DSD090 = 99999) or refused to report the length of use (DSD090 = 77777).

DSD103: In the past 30 days, on how many days did you take the product?

This variable is unedited. Information is missing for dietary supplement data that was recorded in the prescription medication sub-section, since this question is not asked in that sub-section of the DSQ questionnaire.

DSD122Q and DSD122U: On the days that you took the product how much did you usually take on a single day?

The data was edited to standardize the amount the participant reported taking and the amount according to the product 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). There were 336 records in which data was edited.

In most of the cases, using the alternative serving size (information available on some product labels), using simple conversions (i.e., teaspoons to tablespoons) or contacting the manufacturer for information on label serving size (i.e., actual amount for a “capful”) provided enough information to make clear edits. However, in some cases the reported amount taken was very different from the product 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 data entry error. In these cases the reported amount taken was assumed to be the label serving size. There were records in which this occurred and the data was edited to the label serving size. Additionally, all records that were assigned a default product were edited and the label serving size was assigned for DSD122Q and DSD122U.

Information is missing for dietary supplement data that was recorded in the prescription medication sub-section, since this question is not asked in that sub-section of the DSQ questionnaire.

DSDACTSS: Reported serving size/label serving size

This variable was derived using the information from DSD122Q (reported quantity taken) and information from variable DSDSERVQ (serving size quantity from product label) from the “Dietary Supplement Product Information” file (DSPI) of the NHANES-DSD. File DSPI provided information on the serving size from the product label’s supplement facts panel for which the nutrient amounts were based on. The reported amount taken (DSD122Q) was divided by the serving size amount from DSPI (variable DSDSERVQ). Values were set to missing if any information was missing for DSD122Q or DSDSERVQ.

DSDDAY1: Reported Product during the first dietary recall and DSDDAY2: Reported Product during the second dietary recall

For the 2007-2008, 2009-2010, and 2011-2012 release, dietary supplement and non-prescription antacid use was added to the Dietary Interview, which consists of two 24-hour dietary recalls. The first dietary recall interview is collected in-person in the Mobile Examination Center (MEC) and the second interview is collected by telephone 3 to 10 days later. Participants’ were asked about their use of vitamins, minerals, herbals and other DS during the 24-hour period prior to the interview (midnight to midnight). Participants are also asked about their use of non-prescription antacids, because of the calcium and magnesium content of some of these products.

These two variables indicate whether or not the exact DS or antacid was also reported being taken during the first dietary recall (DSDDAY1) and the second dietary recall (DSDDAY2).

DSD124: Took product on own or doctor advised

For the 2007-2008, 2009-2010, and 2011-2012 release, NHANES asked participants the reason or reasons that they are taking DS. For every supplement reported, participants are asked if they are taking the supplement for their own reasons or because a doctor or other healthcare provider told them to. A follow-up question is then asked in order to collect specific reason(s) why the participant is taking the supplement or why their doctor or other healthcare provider told them to take the supplement. The participant is given a hand card with a list of reasons for taking DS and asked to select the reason or reasons.

DSQ128A- DSD128MM: Reason(s) for the taking dietary supplement

These variables indicate the reason(s) for taking each dietary supplement reported. Participants’ are able to choose more than one reason. The participant was shown a hand card (Appendix 7) with a list of reasons. The list was created based on a pilot study done during the NHANES 2006 survey, in which an open-ended question asking about the reason(s) for taking each dietary supplement reported was added. The answers were then used to develop the hand card. If the participant cannot find the reason they are taking the dietary supplement on the hand card, the interviewer indicates “other specified” (which is indicated under variable DSQ128S) and then types in the reason given by the participant. Based on similar “other specified” reasons given in the NHANES 2007-2008 and 2009-2010 survey, more answer categories were also added to the hand card. Analyst should note that answer categories have been slightly modified for this release compared to previous releases. This includes merging into one category “for pregnancy” and “for breastfeeding.” The category “to improve sleep” was added to the category “For relaxation, decrease stress.” The reason “building muscle” was added to the “For muscle related issues” category. The “weight gain” category is now by itself.

Additionally, based on responses given in “other specified,” many were able to be coded into the original response categories. Some other categories were created (denoted by a DSD instead of a DSQ in the variable name) based on many similar responses given. However, there are some exceptions. Variables DSD128T, DSD128AA, DSD128V, DSD128Z, DSD128BB, DSD128DD, and DSD128FF were categories created for the NHANES 2007-2008 and 2009-2010 release, but were added to the hand card for the 2011-2012 NHANES survey. Variable names were retained to make it easier for analyst to combine and use data, but they should be aware that these were categories that were on the hand card beginning in 2011. Additionally, three new categories were added for this release based on similar responses provided in “other specified.” Responses that were not able to be categorized were indicated in variable DSQ128S (other specified) as a code 91.

A few participants entered into “other specified” that they needed to take a supplement because they didn’t get enough sunlight. These responses were back-edited into the “to supplement my diet, food not enough.”

DSQ215A: Antacid, calcium supplement or both?

For the 2007-2008, 2009-2010, and 2011-2012 release, NHANES added a question to collect data on whether the participant is taking the non-prescription antacid reported as an antacid, calcium supplement or both. This question is only asked during the non-prescription antacid sub-section of the DSQ questionnaire. Therefore, there will only be values for antacid products (DSDANTA=2).

Nutrient variables in the Individual Dietary Supplements file, DSQIDS_G

These variables are created by using files from the NHANES_DSD that contain information on the serving size and the quantity of each nutrient from the product label’s supplement facts panel. The participants reported usual amount taken is divided by the serving size from the label in order to determine the actual amount of nutrient consumed. For example, a participant may report taking one tablet, but the serving size amount is 2 tablets. Therefore, only half of the nutrients on the label are being consumed. The variable DSDACTSS (Reported serving size/label serving size) indicates the actual amount of product that was consumed. The actual amount of product consumed is then multiplied by the ingredient amount for each dietary supplement or antacid. In the example above, 0.5 would be multiplied by each ingredient/nutrient to estimate the nutrient intake.

Analysts do need to be aware that in some cases data is missing for the amount consumed.  In these cases, nutrients could not be calculated and are missing. Analyst should be aware of this, especially when estimating the prevalence of use of certain nutrients by using only the nutrient variables.

DSQIFDFE : Folate, DFE (mcg)

Dietary Folate Equivalents (DFE) were calculated by using a conversion factor of 1.7. This conversion is based on recommendations set by the Institute of Medicines Dietary Reference Intakes (Institute of Medicine, 2006).

Nutrient variables in the Total Dietary Supplements files, DSQTOT_G

These variables are created by calculating a mean daily intake. The calculation is based on the number of days the participant reports taking each dietary supplement (variable DSD103). For example, if participant X takes calcium 600 mg 15 days out of the month, the calculation would be 600mg*15 reported days/30 days per month. If participant X took more than one supplement or antacid containing calcium, they would then be added up for the total mean daily calcium intake from DS.

Analysts do need to be aware that in some cases data is missing for the amount consumed and the number of days the supplement was taken. In these cases, nutrients could not be calculated or mean daily intake could not be estimated and therefore values are missing. Analyst should be aware of this, especially when estimating the prevalence of use of certain nutrients by using only the nutrient variables.

Iodine was added to the NHANES 2011-2012 data release files.

In some cases it may appear as though a participant reported the same dietary supplement more than once. There are a several reasons for these duplications. Participants’ may have reported DS with the same generic ingredient but different brand names (i.e. 2 different brands of calcium, but calcium is collected generically with only the strength) or the supplement may have been different forms or dosages of the same product. There were a few cases where the respondent did report the exact same dietary supplement, with the same length of use, frequency of use or amount used. In these cases, since the interviewer recorded that a separate dietary supplement container was seen for each reported dietary supplement both mentions of the dietary supplement were retained in the file.

During the data editing process, outlier values were examined. When there was insufficient information to conclude that values were invalid, they were left in the data set. Analysts should examine the distribution of the data and consider whether or not it is appropriate to include or exclude extreme values in a given analysis.

NCHS collects brand name information on supplements whenever feasible, to ensure as much accuracy as possible in finding the label information for the exact product taken, and providing exact ingredient information for this product to data users. Brand names are not collected for DS listed on the “Strength Only” List (see Appendix 5: Vitamins/Minerals). Only the nutrient is selected and the strength(s) are recorded. Analyst should be aware that for these specific nutrients, NCHS releases generic information (i.e., calcium 600 mg). Thus, analyses of consumer usage by brand name using NHANES data may not be accurate and is not recommended. Brand names that are available in a limited geographic area of the U.S. are not released; generic names are used for these products.

Deriving nutrient estimates from dietary supplement data

Thirty-four nutrients have already been computed for this release. In order to compute average daily intakes for nutrients other than these 34, analyst will need to combine the Individual Dietary Supplements File (DSQIDS_G) with the NHANES-DSD files (DSPI, DSII and DSBI) which contain information on each product and ingredients and amounts in those products.

Intake of multiple supplements with the same nutrient(s), multiple use of the same supplement on the same day, and nutrients in blends should 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.

Analyst need to be aware of question changes over the cycles when looking at trends. Dietary supplement data was reported as times per month in 1999-2000, days in the past month in 2001-2002, and days in the past 30 days in 2003-2012.

Please refer to the on-line NHANES Dietary Tutorial, which is available on the NHANES website, for further details on how to use these datasets.

Estimating total nutrient intakes from all sources (foods, beverages and DS) 

For the 2007-2008, 2009-2010, and 2011-2012 release, data is now collected on the usage of all vitamins, minerals, herbals and other DS as well as non-prescription antacids, as part of the 24-hour recall dietary interviews. Prior to the NHANES 2007-2008 release, estimating total nutrient intakes from all sources (foods, beverages and DS), had been difficult because of the different data collection methods, referent time frames, and data formats. Now with these data collected using similar methods over the same time frame, nutrients from all sources can be easily combined. The improved nutrient estimates will increase researchers’ ability to examine nutrient-disease or nutrient-health associations and to estimate percentages of the population with intakes over or under various nutrient standards. The 24-hour dietary supplement data are released in separate files available on the NHANES dietary website. They can be linked to the dietary files by the respondent sequence number (SEQN). For more information on the data, refer to the documentations accompanying the 24-hour dietary intakes and dietary supplement datasets.