Table 2.
Prevalence and unadjusted and adjusted prevalence ratio of low serum vitamin B12 concentration and biochemically defined vitamin B12 deficiency by B12 supplement dose for adults aged 18–50 years in NHANES III (Third National Health and Nutrition Examination Survey; Phase 2, 1991–4)
| Low serum B12* |
Biochemically defined B12 deficiency† |
|||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| B12-containing supplement use | Prevalence (%) |
95% CI | Unadj. PR |
Adj. PR‡ |
Adj. 95% CI |
Prevalence (%) |
95% CI | Unadj. PR |
Adj. PR§ |
95% CI |
| Adults aged 18–50 years (n 4944∥) | 2·6 | 1·4, 3·8 | – | – | – | 1·2 | 0·5, 1·8 | – | – | – |
| Supplement non-users (n 3768) | 2·9 | 1·6, 4·3 | (referent) | – | – | 1·5 | 0·7, 2·3 | (referent) | – | – |
| Supplement users | ||||||||||
| Any amount (n 1176) | 1·9¶ | 0·5, 3·3 | 0·7 | 0·8 | 0·4, 1·7 | 0·4** | 0·0, 1·1 | 0·3 | 0·5 | 0·1, 2·2 |
| >0 to 6 μg (n 754) | 1·8 (10 cases) |
0·3, 3·2 | 0·6 | 0·8 | 0·4, 1·5 | 0·6 (2 cases) |
0·0, 1·7 | 0·4 | 0·6 | 0·1, 2·9 |
| >6 to 25 μg (n 261) | 2·5 (3 cases) |
0·0, 6·0 | 0·9 | 1·0 | 0·3, 3·3 | 0 (no cases) |
n/a | n/a | <0·001 | n/a |
| >25 μg (n 161) | 1·6 (2 cases) |
0·0, 4·3 | 0·6 | 0·7 | 0·1, 4·8 | 0·3 (1 case) |
0·0, 0·9 | 0·2 | 0·3 | 0·0, 3·5 |
Unadj., unadjusted; Adj., adjusted; PR, prevalence ratio; n/a, not applicable.
The PROCSURVEY FREQ procedure in SAS version 9·1 (SAS Institute Inc., Cary, NC, USA) and the NHANES III, Phase 2 data sets were used to obtain these US population prevalence proportion estimates in adults aged 18–50 years.
Low serum B12: serum B12 <148 pmol/l.
Biochemically defined B12 deficiency: serum B12 <148 pmol/l with serum homocysteine >10 μmol/l.
Adj. PR=prevalence ratio adjusted for age (continuous), gender, race (black race or other), folate deficiency status and education (<8 years v. >8 years).
Adj. PR=prevalence ratio adjusted for age (continuous), gender, race (black race or other), folate deficiency status, serum creatinine and education (<8 years v. >8 years).
Estimates are based on 7404 survey participants for the biochemical B12 deficiency analysis and on 8376 survey participants for the low B12 analysis.
Rao–Scott P value=0·2 compared with supplement non-users.
Rao–Scott P value=0·06 compared with supplement non-users.