TABLE 3.
Categories of decreasing plasma methylmalonic acid (MMA) concentrations and descriptions of demographic, biochemical, dietary, medication, and cognitive variables in the US population, 1999–20041
| Plasma MMA | ||||
| >376 nmol/L | 272–376 nmol/L | 210–271 nmol/L | <210 nmol/L | |
| No. of subjects | 375 | 451 | 1042 | 10,744 |
| Subjects per group (%) | 2.3 | 3.4 | 8.1 | 86.2 |
| Demographic characteristic2 | ||||
| Age (y) | 57 ± 13 | 52 ± 1 | 51 ± 1 | 44 ± 14 |
| >60 y (%) | 47 ± 4 | 38 ± 3 | 34 ± 2 | 18 ± 14 |
| Male sex (%) | 53 ± 4 | 50 ± 3 | 52 ± 2 | 49 ± 1 |
| Non-Hispanic white (%) | 69 ± 4 | 80 ± 3 | 78 ± 2 | 71 ± 2 |
| Non-Hispanic black (%) | 4 ± 1 | 4 ± 1 | 6 ± 1 | 11 ± 14 |
| Mexican American (%) | 8 ± 2 | 4 ± 1 | 5 ± 1 | 7 ± 1 |
| Serum vitamin B-12 (pmol/L)25 | 224 ± 11 | 294 ± 11 | 339 ± 21 | 406 ± 94 |
| <148 pmol/L (%)25 | 27 ± 3 | 9 ± 2 | 5 ± 1 | 2 ± 0.14 |
| <200 pmol/L (%)25 | 49 ± 3 | 33 ± 3 | 19 ± 2 | 8 ± 0.44 |
| <258 pmol/L (%)25 | 66 ± 3 | 50 ± 3 | 40 ± 2 | 19 ± 14 |
| Total homocysteine (μmol/L)25 | 13.4 ± 1 | 10.5 ± 0.2 | 9.4 ± 0.1 | 8.3 ± 0.54 |
| High, >13 μmol/L (%) | 40 ± 4 | 18 ± 2 | 10 ± 1 | 4 ± 0.34 |
| Folate status25 | ||||
| Red blood cell folate (nmol/L) | 550 ± 18 | 600 ± 21 | 653 ± 11 | 674 ± 74 |
| Serum folate (nmol/L) | 28.6 ± 1.2 | 28.4 ± 1.2 | 29.8 ± 0.8 | 32.9 ± 0.54 |
| High folate, >59 nmol/L (%) | —6 | 8.3 ± 1.5 | 7.3 ± 1.1 | 9.7 ± 0.54 |
| Diet and supplements | ||||
| User of vitamin B-12 supplements (%) | 13 ± 3 | 18 ± 3 | 21 ± 2 | 26 ± 14 |
| Vitamin B-12 (μg/d)7 | 29 ± 5 | 40 ± 9 | 43 ± 9 | 45 ± 44 |
| Vitamin B-12, diet (μg/d) | 5.0 ± 0.7 | 4.7 ± 0.2 | 4.6 ± 0.2 | 5.3 ± 0.14 |
| Total vitamin B-12 (μg/d) | 5.6 ± 1.8 | 9.6 ± 1.6 | 12.2 ± 2.2 | 17.5 ± 1.24 |
| Prescription medication use (%)2 | ||||
| Proton pump inhibitors | 3.3 ± 1.2 | 4.8 ± 1.2 | 7.9 ± 1.0 | 5.8 ± 0.3 |
| H2-Receptor antagonists | —6 | 3.5 ± 1.1 | 2.4 ± 0.6 | 1.9 ± 0.2 |
| Either of the above medications | 4.8 ± 1.6 | 8.3 ± 1.5 | 10.3 ± 1.2 | 7.7 ± 0.3 |
| Cognitive scores38 | 41 ± 2 | 42 ± 1 | 47 ± 1 | 48 ± 14 |
| DSC <34 points (%) | 41 ± 6 | 34 ± 4 | 28 ± 4 | 22 ± 14 |
| Age >60 y, 1999–2002 (n) | 135 | 120 | 306 | 1832 |
We combined the data for adults aged ≥19 y (n = 16,184) from NHANES 1999–2000, 2001–2002, and 2003–2004. We excluded data from respondents with interview data only (ie, no mobile examination center data, RIDSTATR = 1; n = 1160), high creatinine concentrations (>120 μmol/L for men, >110 μmol/L for women; n = 548), and missing MMA data (n = 918). We also excluded data for lactating (n = 145) and pregnant (n = 801) women. The analytic sample included data for 12,612 respondents. NHANES assessed serum vitamin B-12 by using the Quantaphase II radioassay from Bio-Rad (Hercules, CA), plasma MMA by using gas chromatography–mass spectrometry, and plasma homocysteine with a fluorescence polarization immunoassay reagent kit from Abbott Laboratories (Abbott Park, IL). DSC, Digit Symbol-Coding.
This analysis was controlled for age, sex, and race-ethnicity.
Least-squares mean ± SE (all such values).
Significant linear trend across MMA groups. We log-transformed nonnormal variables before statistical analysis, P ≤ 0.05.
This analysis controlled for serum creatinine concentration, session of blood collection, and hours of fasting before blood collection.
The relative SE was >40%, which is not reliable.
Estimates are for users of dietary supplements only; total is for users and nonusers of supplements combined.
Based on the DSC subtest of the Wechsler Adult Intelligence Scale III (The Psychological Corporation, San Antonio, TX). Cognitive function scores were available for those aged ≥60 y in NHANES 1999–2002 (n = 2393).