New research links optimal vit D to higher verbal fluency. Taken from the Vit D council website...
"Petterson concluded (in research published in December):
“ vitamin D levels exceeding 100 nmol/L (40 ng/ml) were found to be associated with significantly better performance on a verbal (phonemic) fluency task, which primarily assesses executive functioning. This implies that the optimal level for cognition is higher than that for bone health, and higher than previous studies have suggested. Spline analyses suggest that the relationship is not entirely linear, with an optimal level possibly around 120 nmol nmol/L (50 mg/ml).”
Hypothyroidism slows speech along with everything else, of course, but getting D levels up could help along with optimal thyroid treatment.