• Component Description
• Eligible Sample
• Description of Laboratory Methodology
• Laboratory Quality Assurance and Monitoring
• Data Processing and Editing
• Analytic Notes
• References
• Codebook
  • SEQN - Respondent sequence number
  • WTSSCAF2 - Surplus specimen caffeine 2 year weights
  • WTSSCAF4 - Surplus specimen caffeine 4 year weights
  • SSMU1 - 1-methyluric acid (umol/L)
  • SSMU1LC - 1-methyluric acid comment code
  • SSMU3 - 7-methyluric acid (umol/L)
  • SSMU3LC - 7-methyluric acid comment code
  • SSMU4 - 1,3-dimethyluric acid (umol/L)
  • SSMU4LC - 1,3-dimethyluric acid comment code
  • SSMU5 - 1,7-dimethyluric acid (umol/L)
  • SSMU5LC - 1,7-dimethyluric acid comment code
  • SSMU6 - 3,7-dimethyluric acid (umol/L)
  • SSMU6LC - 3,7-dimethyluric acid comment code
  • SSMU7 - 1,3,7-trimethyluric acid (umol/L)
  • SSMU7LC - 1,3,7-trimethyluric acid comment code
  • SSMX1 - 1-methylxanthine (umol/L)
  • SSMX1LC - 1-methylxanthine comment code
  • SSMX2 - 3-methylxanthine (umol/L)
  • SSMX2LC - 3-methylxanthine comment code
  • SSMX3 - 7-methylxanthine (umol/L)
  • SSMX3LC - 7-methylxanthine comment code
  • SSMX4 - 1,3-dimethylxanthine(theophylline)umol/L
  • SSMX4LC - 1,3-dimethylxanthine comment code
  • SSMX5 - 1,7-dimethylxanthine(paraxanthine)umol/L
  • SSMX5LC - 1,7-dimethylxanthine comment code
  • SSMX6 - 3,7-dimethylxanthine(theobromine)umol/L
  • SSMX6LC - 3,7-dimethylxanthine comment code
  • SSMX7 - 1,3,7-trimethylxanthine(caffeine)umol/L
  • SSMX7LC - 1,3,7-trimethylxanthine comment code
  • SSAMU - 5-actylamino-6-amno-3-methyluracil(uM/L)
  • SSAMULC - 5-actylamno-6-amno-3-methylucl cmnt code

National Health and Nutrition Examination Survey

2001-2002 Data Documentation, Codebook, and Frequencies

Caffeine & Caffeine Metabolites - Urine (Surplus) (SSCAFE_B)

Data File: SSCAFE_B.xpt

First Published: December 2024

Last Revised: NA

Component Description

Caffeine is an alkaloid that is known to have psychoactive stimulatory effects. Caffeine naturally occurs in plants (e.g., coffee beans, tea leaves, cocoa beans, cola nuts), and the dietary consumption of caffeine originates mainly from derivative beverages (e.g., coffee, tea, cola drinks) and foods (e.g., chocolate). Caffeine is also used as a food additive in beverages (e.g., caffeinated soft drinks, “energy” drinks) and as a drug either on its own or as an adjuvant in certain medications (e.g., analgesics) (Fredholm, et. al., 1999).

Given the high prevalence of behaviorally active caffeine doses in the worldwide diet, significant scientific interest in the health effects of caffeine has developed. As a psychoactive stimulant, the behavioral effects of caffeine, such as its effect on mental alertness, have been studied extensively, and topics such as caffeine tolerance, addiction, and withdrawal have also been examined. Caffeine consumption has been studied as a risk factor for many diseases and conditions, including hypertension, bone density, cardiovascular diseases, various cancers, reproduction and developmental abnormalities, and mental and behavioral disorders (Nawrot, et. al., 2003; Wikoff, et. al., 2017; Grosso, et. al., 2017).

Eligible Sample

Examined participants aged 6 years and older from a one-third sample were eligible.

Description of Laboratory Methodology

Caffeine and 13 of its metabolites are quantified in urine by use of high-performance liquid chromatography-electrospray ionization-tandem quadrupole mass spectrometry (HPLC-ESI-MS/MS) with stable isotope labeled internal standards. A 50-µL aliquot of urine is first diluted with 450 µL of water. Then, 100 µL of the diluted urine is combined with 120 µL of a 0.2 N NaOH solution containing stable isotope labeled internal standards. The mixture is incubated for at least 30 min at room temperature, facilitating the conversion of an unstable uracil metabolite into a more stable form. Samples are then acidified with 30 µL of 2.0 N HCl and 250 µL of a 1:9 methanol/water solution containing 0.1% formic acid such that the matrix of the sample is similar to the starting mobile phase composition of the analysis step. Samples are filtered and analyzed by use of HPLC-ESI-MS/MS in both positive and negative ionization modes. Quantitation is based on peak area ratios interpolated against an 11-point calibration curve derived from calibrators in synthetic urine.   

The lab method, lab equipment, and lab site used for this surplus component were unchanged from the NHANES 1999–2000, 2011–2012, and 2013–2014 cycles.

Laboratory Quality Assurance and Monitoring

The laboratory in which these analyses were performed was certified according to the Clinical Laboratory Improvement Amendments of 1988 (CLIA). CLIA certification applied to all facilities, procedures, personnel, quality systems, and proficiency testing associated with these analyses.

In-house prepared urine quality control (QC) pools at three levels were analyzed in every run in duplicate and evaluated againstperformance criteria established by the Division of Laboratory Sciences for accuracy and precision, similar to the Westgard rules (Caudill, et. al., 2008).

Performance of QC pools during the study period:

QC Pool	Analyte	n	Mean (µmol/L)	SD (µmol/L)	CV (%)	Difference to target (%)
LU17560_C	SSMU1	20	25.7	2.3	8.8	-2.6
LU17560_D	SSMU1	32	26.0	2.7	10.5	-0.6
LU17560_E	SSMU1	128	25.7	2.0	7.8	-1.4
LU17560_F	SSMU1	30	25.3	1.8	7.0	-0.5
MU17561_C	SSMU1	20	62.1	4.5	7.2	-3.3
MU17561_D	SSMU1	32	64.0	6.3	9.8	0.8
MU17561_E	SSMU1	128	62.1	4.8	7.7	-2.2
MU17561_F	SSMU1	30	61.1	5.1	8.4	-1.3
HU17562_C	SSMU1	20	150	10	6.7	1.3
HU17562_D	SSMU1	32	147	15	9.9	-1.4
HU17562_E	SSMU1	128	149	14	9.3	0.1
HU17562_F	SSMU1	30	150	13	8.8	1.1

 

QC Pool	Analyte	n	Mean (µmol/L)	SD (µmol/L)	CV (%)	Difference to target (%)
LU17560_C	SSMU3	20	6.72	0.6	9	-4.6
LU17560_D	SSMU3	32	7.28	0.64	8.8	7.2
LU17560_E	SSMU3	128	7.02	0.59	8.4	3.5
LU17560_F	SSMU3	30	7.04	0.55	7.8	0.7
MU17561_C	SSMU3	20	12.7	1.3	10	-5.7
MU17561_D	SSMU3	32	14.5	1.1	7.7	11.2
MU17561_E	SSMU3	128	13.6	1.1	8	4.4
MU17561_F	SSMU3	30	13.1	0.9	6.8	-3.6
HU17562_C	SSMU3	20	21.4	1.6	7.7	-2
HU17562_D	SSMU3	32	22.2	2.3	10.6	3.8
HU17562_E	SSMU3	128	21.5	1.8	8.3	0.5
HU17562_F	SSMU3	30	21.6	1.8	8.4	1.6

 

QC Pool	Analyte	n	Mean (µmol/L)	SD (µmol/L)	CV (%)	Difference to target (%)
LU17560_C	SSMU4	22	2.57	0.19	7.3	-1.5
LU17560_D	SSMU4	32	2.6	0.17	6.6	0.5
LU17560_E	SSMU4	120	2.56	0.16	6.1	-1
LU17560_F	SSMU4	30	2.51	0.13	5.2	0.8
MU17561_C	SSMU4	22	9.39	0.58	6.1	-1.9
MU17561_D	SSMU4	32	9.59	0.64	6.6	1.9
MU17561_E	SSMU4	120	9.16	0.53	5.7	-2.7
MU17561_F	SSMU4	30	8.92	0.53	5.9	-0.3
HU17562_C	SSMU4	22	19.8	0.9	4.6	-5.2
HU17562_D	SSMU4	32	20.1	1.2	6.2	-0.7
HU17562_E	SSMU4	120	19.7	1.2	6.3	-2.7
HU17562_F	SSMU4	30	19.0	1.0	5.4	-2

 

QC Pool	Analyte	n	Mean (µmol/L)	SD (µmol/L)	CV (%)	Difference to target (%)
LU17560_C	SSMU5	20	10.5	0.4	4.1	-1.7
LU17560_D	SSMU5	32	10.6	0.5	4.9	0.2
LU17560_E	SSMU5	128	10.3	0.5	4.8	-2.1
LU17560_F	SSMU5	30	10.2	0.4	3.8	-0.2
MU17561_C	SSMU5	20	36	1.6	4.3	-2.8
MU17561_D	SSMU5	32	36.7	2.2	6.1	0.7
MU17561_E	SSMU5	128	35.8	1.6	4.6	-1.8
MU17561_F	SSMU5	30	34.9	1.7	5.0	-2.7
HU17562_C	SSMU5	20	80.2	3.9	4.9	-3.3
HU17562_D	SSMU5	32	81.5	4.9	6.0	0.5
HU17562_E	SSMU5	128	80	4.1	5.1	-1.4
HU17562_F	SSMU5	30	80.1	3.9	4.9	0.4

 

QC Pool	Analyte	n	Mean (µmol/L)	SD (µmol/L)	CV (%)	Difference to target (%)
LU17560_C	SSMU6	22	0.374	0.048	12.8	-5.9
LU17560_D	SSMU6	32	0.39	0.046	11.8	2.3
LU17560_E	SSMU6	128	0.385	0.045	11.7	0.8
LU17560_F	SSMU6	30	0.376	0.051	13.5	-3.4
MU17561_C	SSMU6	22	1.16	0.09	8.1	-0.6
MU17561_D	SSMU6	32	1.18	0.11	9.1	2.6
MU17561_E	SSMU6	128	1.12	0.11	9.6	-2.7
MU17561_F	SSMU6	30	1.11	0.09	8.2	-1.8
HU17562_C	SSMU6	22	1.46	0.16	11	-5.5
HU17562_D	SSMU6	32	1.55	0.15	9.6	5.8
HU17562_E	SSMU6	128	1.47	0.13	8.6	-0.1
HU17562_F	SSMU6	30	1.48	0.11	7.2	1.5

 

QC Pool	Analyte	n	Mean (µmol/L)	SD (µmol/L)	CV (%)	Difference to target (%)
LU17560_C	SSMU7	20	0.971	0.036	3.7	-1.1
LU17560_D	SSMU7	32	0.994	0.037	3.7	2.4
LU17560_E	SSMU7	124	0.972	0.041	4.2	0.2
LU17560_F	SSMU7	30	0.956	0.035	3.7	1.1
MU17561_C	SSMU7	20	3.74	0.14	3.7	-1.7
MU17561_D	SSMU7	32	3.79	0.14	3.6	1.0
MU17561_E	SSMU7	124	3.77	0.16	4.2	0.3
MU17561_F	SSMU7	30	3.62	0.16	4.3	-1.5
HU17562_C	SSMU7	20	7.44	0.42	5.7	-3
HU17562_D	SSMU7	32	7.58	0.33	4.4	1
HU17562_E	SSMU7	124	7.51	0.43	5.7	0.1
HU17562_F	SSMU7	30	7.47	0.36	4.8	1.7

 

QC Pool	Analyte	n	Mean (µmol/L)	SD (µmol/L)	CV (%)	Difference to target (%)
LU17560_C	SSMX1	16	15.8	0.6	4.0	1.5
LU17560_D	SSMX1	30	16.1	0.7	4.4	3.7
LU17560_E	SSMX1	124	15.4	0.9	5.6	-1.7
LU17560_F	SSMX1	30	15.2	0.6	4.2	0.3
MU17561_C	SSMX1	16	42.8	1.9	4.5	1.4
MU17561_D	SSMX1	30	43.7	2.1	4.7	3.2
MU17561_E	SSMX1	124	41.4	2.2	5.2	-1.2
MU17561_F	SSMX1	30	40.1	1.7	4.3	-2.6
HU17562_C	SSMX1	16	101	4.1	4.1	-2.3
HU17562_D	SSMX1	30	102	5.8	5.6	1.1
HU17562_E	SSMX1	124	99.8	6.4	6.4	-3.6
HU17562_F	SSMX1	30	93.7	5.6	6.0	-3.3

 

QC Pool	Analyte	n	Mean (µmol/L)	SD (µmol/L)	CV (%)	Difference to target (%)
LU17560_C	SSMX2	18	10.9	0.6	5.7	-0.3
LU17560_D	SSMX2	32	11	0.9	8.1	1
LU17560_E	SSMX2	126	10.6	0.7	6.3	-2.7
LU17560_F	SSMX2	28	10.4	0.5	4.8	1.1
MU17561_C	SSMX2	18	28.7	1.4	5.0	-1.0
MU17561_D	SSMX2	32	28.7	2.0	7	0.4
MU17561_E	SSMX2	126	28	1.4	5.1	-2.0
MU17561_F	SSMX2	28	27	1.6	6.1	-3.3
HU17562_C	SSMX2	18	46.7	3.2	6.8	0.2
HU17562_D	SSMX2	32	46.4	3.5	7.6	1.6
HU17562_E	SSMX2	126	44.5	2.9	6.6	-2.4
HU17562_F	SSMX2	28	44.7	2.5	5.6	0.9

 

QC Pool	Analyte	n	Mean (µmol/L)	SD (µmol/L)	CV (%)	Difference to target (%)
LU17560_C	SSMX3	20	21	0.9	4.5	-2.7
LU17560_D	SSMX3	30	21.9	1.5	6.6	3.4
LU17560_E	SSMX3	124	21.8	1.6	7.5	2.6
LU17560_F	SSMX3	30	21.5	1.4	6.7	-0.7
MU17561_C	SSMX3	20	47.4	2	4.3	-3.5
MU17561_D	SSMX3	30	49.1	3.5	7.1	2.7
MU17561_E	SSMX3	124	48.1	3.4	7	0.7
MU17561_F	SSMX3	30	46.8	3	6.5	-2.3
HU17562_C	SSMX3	20	74.9	4.1	5.5	-2.8
HU17562_D	SSMX3	30	75.4	3.1	4.1	0.2
HU17562_E	SSMX3	124	75.7	5.1	6.8	0.6
HU17562_F	SSMX3	30	75.7	5.6	7.3	0.6

 

QC Pool	Analyte	n	Mean (µmol/L)	SD (µmol/L)	CV (%)	Difference to target (%)
LU17560_C	SSMX4	22	1.19	0.05	4.3	-0.2
LU17560_D	SSMX4	30	1.24	0.06	4.7	3.6
LU17560_E	SSMX4	116	1.16	0.06	5.1	-2.7
LU17560_F	SSMX4	30	1.14	0.04	3.3	0.5
MU17561_C	SSMX4	22	3.47	0.14	4	-3.5
MU17561_D	SSMX4	30	3.66	0.2	5.5	3.6
MU17561_E	SSMX4	116	3.47	0.16	4.5	-1.6
MU17561_F	SSMX4	30	3.32	0.18	5.3	-2.7
HU17562_C	SSMX4	22	6.73	0.25	3.7	-6.1
HU17562_D	SSMX4	30	6.93	0.38	5.6	0.3
HU17562_E	SSMX4	116	6.77	0.38	5.5	-2.1
HU17562_F	SSMX4	30	6.57	0.27	4.2	-0.7

 

QC Pool	Analyte	n	Mean (µmol/L)	SD (µmol/L)	CV (%)	Difference to target (%)
LU17560_C	SSMX5	14	13.6	0.3	2.3	-1.9
LU17560_D	SSMX5	30	14	0.6	4	3.1
LU17560_E	SSMX5	118	13.9	0.6	4.1	2.1
LU17560_F	SSMX5	26	13.6	0.4	2.8	-1.3
MU17561_C	SSMX5	14	37.7	0.8	2.2	-3.3
MU17561_D	SSMX5	30	38.9	1.7	4.4	2.4
MU17561_E	SSMX5	118	37.9	1.4	3.7	-0.1
MU17561_F	SSMX5	26	36.6	1.3	3.6	-2.5
HU17562_C	SSMX5	14	70.1	2.4	3.4	-2.9
HU17562_D	SSMX5	30	71.3	3.3	4.6	1.8
HU17562_E	SSMX5	118	69.1	3.2	4.6	-1.4
HU17562_F	SSMX5	26	68.5	2.6	3.9	1.1

 

QC Pool	Analyte	n	Mean (µmol/L)	SD (µmol/L)	CV (%)	Difference to target (%)
LU17560_C	SSMX6	16	11.3	0.3	3.1	-1.1
LU17560_D	SSMX6	32	11.4	0.5	4	1
LU17560_E	SSMX6	120	11.1	0.5	4.4	-2
LU17560_F	SSMX6	30	11	0.5	4.7	0.5
MU17561_C	SSMX6	16	36.8	1.5	4.1	-1.6
MU17561_D	SSMX6	32	37.7	2	5.4	1.8
MU17561_E	SSMX6	120	36	1.7	4.8	-2.8
MU17561_F	SSMX6	30	35.4	1.8	5	-0.1
HU17562_C	SSMX6	16	35.9	1.7	4.7	-3.8
HU17562_D	SSMX6	32	36.5	2	5.4	0.9
HU17562_E	SSMX6	120	35.5	1.6	4.5	-2
HU17562_F	SSMX6	30	35.6	1.6	4.6	1.2

 

QC Pool	Analyte	n	Mean (µmol/L)	SD (µmol/L)	CV (%)	Difference to target (%)
LU17560_C	SSMX7	22	4.15	0.12	2.9	-0.3
LU17560_D	SSMX7	30	4.19	0.1	2.3	0.7
LU17560_E	SSMX7	122	4.11	0.15	3.7	-1.3
LU17560_F	SSMX7	30	4.06	0.12	3	-0.1
MU17561_C	SSMX7	22	23.2	0.9	4.1	-0.6
MU17561_D	SSMX7	30	23.5	0.9	3.6	0.9
MU17561_E	SSMX7	122	23	0.9	3.8	-1.1
MU17561_F	SSMX7	30	22.3	0.9	3.8	-2.5
HU17562_C	SSMX7	22	28.5	1.4	4.7	-1.6
HU17562_D	SSMX7	30	28.8	1	3.6	0.1
HU17562_E	SSMX7	122	28.5	1.3	4.7	-0.8
HU17562_F	SSMX7	30	28.5	1.3	4.4	0.5

 

QC Pool	Analyte	n	Mean (µmol/L)	SD (µmol/L)	CV (%)	Difference to target (%)
LU17560_C	SSAMU	18	25.7	1.5	5.9	-8.4
LU17560_D	SSAMU	32	26.5	1.9	7.1	0.3
LU17560_E	SSAMU	120	24.5	1.7	7.1	-7
LU17560_F	SSAMU	30	24.7	1.6	6.4	1.2
MU17561_C	SSAMU	18	57.5	2.8	5	-7.5
MU17561_D	SSAMU	32	58.6	3.8	6.5	-0.1
MU17561_E	SSAMU	120	56.5	3.7	6.5	-3.8
MU17561_F	SSAMU	30	55.1	3.1	5.7	-2
HU17562_C	SSAMU	18	184	11	5.9	-6.1
HU17562_D	SSAMU	32	189	12	6.6	0.6
HU17562_E	SSAMU	120	182	10	5.5	-3
HU17562_F	SSAMU	30	180	10	5.3	1

Data Processing and Editing

Data were received after all analyses were complete. The data were reviewed. Incomplete data or improbable values were sent to the performing laboratory for confirmation.

Analytic Notes

Refer to the 2001 – 2002 Laboratory Data Overview for general information on NHANES laboratory data.

There are over 800 laboratory tests performed on NHANES participants. However, not all participants provided biospecimens or enough volume for all the tests to be performed. Additionally, availability of specimens for surplus projects is lower than for other laboratory tests performed on NHANES participants. The specimen availability can also vary by age or other population characteristics. Analysts should evaluate the extent of missing data in the dataset related to the outcome of interest as well as any predictor variables used in the analyses to determine whether additional re-weighting for item non-response is necessary.

Please refer to the NHANES Analytic Guidelines and the on-line NHANES Tutorial for further details on the use of sample weights and other analytic issues.

Subsample Weights

The analytes included in this dataset were measured in a one-third subsample of participants 6 years and older. Special sample weights are required to analyze these data properly. Specific sample weights for this subsample, WTSSCAF2 and WTSSCAF4, are included in this data file and should be used when analyzing these data. The sample weights created for this file used the phthalate one-third subsample sample weight, i.e., WTSPH2YR or WTSPH4YR, as the base weight. The base weight was adjusted for additional nonresponse to these lab tests and re-poststratified to the population total using sex, age, and race/Hispanic origin. Participants who were part of the eligible population but who did not provide a urine specimen, or did not have sufficient volume of biospecimens, or who did not give consent for their specimens to be used for future research are included in the file, but they have a sample weight assigned “0” in their records. Several participants have a sample weight assigned “0”, but have non-missing analyte data because their originally assigned base weight (i.e. WTSPH2YR or WTSPH4YR) was “0”. The dataset includes 2-year and 4-year subsample weights. The 4-year weights should be used if 1999-2000 data are combined with 2001–2002 data.

Demographic and Other Related Variables

The analysis of NHANES laboratory data must be conducted using the appropriate survey design and demographic variables. The NHANES 2001-2002 Demographics File contains demographic data, health indicators, and other related information collected during household interviews as well as the sample design variables. The recommended procedure for variance estimation requires use of stratum and PSU variables (SDMVSTRA and SDMVPSU, respectively) in the demographic data file.

This laboratory data file can be linked to the other NHANES data files using the unique survey participant identifier (i.e., SEQN).

Detection Limits

The detection limit was constant for all of the analytes in the data set. Two variables are provided for each of these analytes. The variable name ending in “LC” (ex., SSMU1LC) indicates whether the result was below the limit of detection: the value “0” means that the result was at or above the limit of detection, “1” indicates that the result was below the limit of detection. The other variable (ex., SSMU1) provides the analytic result for that analyte. For analytes with analytic results below the lower limit of detection (ex., SSMUC1LC=1), an imputed fill value was placed in the analyte results field. This value is the lower limit of detection divided by square root of 2 (LLOD/sqrt[2]).

The lower limits of detection (LLOD, in umol/L) for urinary caffeine and caffeine metabolites:

Variable Name	SAS Label	LLOD
SSMU1	1-methyluric acid (umol/L)	0.2
SSMU3	7-methyluric acid (umol/L)	0.2
SSMU4	1,3-dimethyluric acid (umol/L)	0.03
SSMU5	1,7-dimethyluric acid (umol/L)	0.04
SSMU6	3,7-dimethyluric acid (umol/L)	0.07
SSMU7	1,3,7-trimethyluric acid (umol/L)	0.005
SSMX1	1-methylxanthine (umol/L)	0.02
SSMX2	3-methylxanthine (umol/L)	0.04
SSMX3	7-methylxanthine (umol/L)	0.02
SSMX4	1,3-dimethylxanthine(theophylline)umol/L	0.03
SSMX5	1,7-dimethylxanthine(paraxanthine)umol/L	0.007
SSMX6	3,7-dimethylxanthine(theobromine)umol/L	0.01
SSMX7	1,3,7-trimethylxanthine(caffeine)umol/L	0.06
SSAMU	5-actylamino-6-amno-3-methyluracil(uM/L)	0.3

References

• Caudill S.P., Schleicher R.L., Pirkle J.L. Multi-rule quality control for the age-related eye disease study. Stat. Med. (2008) 27(20):4094-106.
• Fredholm B.B., Bättig K., Holmén J., Nehlig A., Zvartau E.E. Actions of caffeine in the brain with special reference to factors that contribute to its widespread use. Pharmacol. Rev. (1999) Mar;51(1):83-133.
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Codebook and Frequencies