TABLE 2.
Demographic, biochemical, and dietary variables by change points determined with the linear-splines approach among US adults, 1999–20041
| Serum vitamin B-12 concentrations |
|||
| <126 pmol/L(n = 157) | 126–287 pmol/L(n = 3957) | >287 pmol/L(n = 8569) | |
| Percentage of sample (%) | 1 | 33 | 66 |
| Demographic characteristics2 | |||
| Age (y) | 53 ± 1a,3 | 45 ± 0.3b | 46 ± 0.3c |
| ≥60 y (%) | 37 ± 4a | 21 ± 1b | 23 ± 1c |
| Male (%) | 37 ± 5a | 48 ± 1b | 51 ± 1c |
| Non-Hispanic white (%) | 81 ± 4a | 76 ± 2a | 70 ± 2b |
| Non-Hispanic black (%) | 6 ± 2a | 7 ± 1a | 12 ± 1b |
| Mexican American (%) | 5 ± 1a | 6 ± 1a | 8 ± 1b |
| Biochemical variables4 | |||
| Plasma MMA (nmol/L) | 719 ± 113a | 176 ± 2b | 137 ± 2c |
| Median (nmol/L) | 281 (245, 366) | 148 (140, 153) | 120 (119, 125) |
| Plasma tHcy (μmol/L) | 17 ± 2a | 10 ± 0.1b | 8 ± 0.1c |
| Median (μmol/L) | 12 (10.9, 13.1) | 9 (8.5, 8.8) | 8 (7.6, 7.8) |
| Dietary components | |||
| Vitamin B-12 from food sources (μg/d) | 4.7 ± 0.5 | 4.7 ± 0.2 | 5.5 ± 0.1 |
| Median (μg/d) | 3.1 (2.5, 3.6) | 3.4 (3.3, 3.6) | 4.1 (3.9, 4.3) |
| Vitamin B-12 from dietary supplements (μg/d)5 | 10.3 ± 1.5a | 38.8 ± 9.1b | 75.4 ± 13.1c |
| Median (μg/d) | 5.9 (5.6, 8.0) | 6.0 (5.9, 6.0) | 9.9 (8.8, 11.8) |
| Percentage using vitamin B-12 supplements (%) | 24 ± 4a | 24 ± 1a | 45 ± 1b |
| Total vitamin B-12 intake (μg/d) | 7.2 ± 0.7a | 14.4 ± 2.3b | 39.6 ± 6.2c |
| Median (μg/d) | 3.7 (3.3, 5.9) | 4.5 (4.3, 4.8) | 7.7 (7.6, 7.8) |
Data from NHANES 1999–2000, 2001–2002, and 2003–2004 (n = 31,126) were combined. Data for participants younger than 19 y (n = 14,942); those with only interview data (n = 1160); lactating (n = 145) and pregnant (n = 802) females; those with missing data on MMA (n = 928), serum vitamin B-12 (n = 114), or creatinine (n = 107) concentrations; those with a serum vitamin B-12 concentration greater than the 99th percentile (>1265 pmol/L; n = 135); and those with a glomerular filtration rate <30 (n = 110) were excluded. The final analytic sample size was 12,683. 95% CIs in parentheses. Values in a row with different superscript letters are significantly different, P ≤ 0.05 [determined by a diffvar statement in PROC DESCIPT (SAS-callable Sudann)]. MMA, methylmalonic acid; tHcy, total homocysteine.
Percentages do not add up to 100 because data for the “other” racial-ethnic group are not presented.
Mean ± SE (all such values).
NHANES assessed serum vitamin B-12 concentrations by using the Quantaphase II radioassay from BioRad, plasma MMA concentrations by using gas chromatography–mass spectrometry, and plasma homocysteine concentrations by using a fluorescence polarization immunoassay reagent kit from Abbott Laboratories.
Estimates are for users of dietary supplements only; the total is for users and nonusers of supplements combined.