Serum vitamin B12 and folic acid levels in hyperthyroidism.

Serum vitamin B12 and folic acid levels were measured in 48 hyperthyroid patients and in a group of euthyroid controls. The levels of vitamin B12 ranged from 120-900 pg/ml with a mean of 429.3 +/- 30.9 pg/ml (SE). The mean serum vitamin B12 level was lower in hyperthyroid patients than in normal controls, the difference being statistically significant (t = 2.584, p less than 0.025). Serum vitamin B12 levels showed a statistically significant negative correlation with the clinical index of Grooks et al. (r = 0.344, p less than 0.05). The findings, although not excluding the involvement of auto-immune gastritis in patients with low serum vitamin B12 levels, suggest a direct action of increased thyroid hormone concentrations. Serum folic acid levels ranged from 0.5-13.8 ng/ml with a mean of 6.8 +/- 0.46 ng/ml (SE). The mean serum folic acid levels were higher in the hyperthyroid patients than in normal controls but the difference was not statistically significant (t = 1.2, p greater than 0.2). The serum folic acid levels did not show any statistically significant correlation with the clinical index of Grooks et al. The fact that no statistically significant difference was found between the mean value in hyperthyroid patients and the mean value in normal controls is probably due to the high folic acid intake in Greece.