A randomized controlled trial in 167 older adults (50 years) found two-year supplementation with vitamin B 12 (10 g/day), along with folic acid (200 g/day), vitamin B6 (10 mg/day), riboflavin (5 mg/day), and vitamin D (10 g/day), had no effect on bone mineral density (total hip, femoral neck, or lumbar spine) compared to the control group only receiving vitamin D (10 g/day ) (116)
In Downs syndrome, despite having 3 copies of the AIRE gene, expression of thyroid antigens in the thymus is reduced, and this is thought to cause the elevated incidence of autoimmunity in these patients (87)
That is 20 weeks at the starting dose, or 10 weeks if you have titrated up to 0.5mg
Volpi, E., Nazemi, R., & Fujita, S