What dose if vitamin d is safe to take with synthroid. and does vitamin d help with weight loss ?

Vitamin D..: The usual recommended daily dose of vitamin D is between 1000 to 4000 IU unless you are significantly deficient. It is however important not to take excessive amounts since too much could be toxic so in order to take more than 4000 u discuss with your doctor and levels should be measured. It's role in weight or weight loss is not fully clear though.