Can Excessive Vitamin D Impair The Hair Growth?
No
Detailed Answer:
Excess vitamin D is not known to stop hair growth.
I see you are on thyroid medications. Just make sure your thyroid blood tests are fine because an inadequately treated thyroid can cause hair problems.
The 1200/600 calcium/D preparation you take seem all right. An individuals' daily dietary calcium intake determines whether or not (s)he needs supplements, and if yes,what dose of supplements.
So you may wish to see a dietitian to learn what is your current dietary calcium intake on a daily basis. If it is less than 1200 mg daily then you need to either further increase your dietary intake or increase the dose of calcium in your supplements.
Regarding the daily 5000 IU vitamin D supplement, it is important to go by blood levels. A 25 hydroxy vitamin D blood test will provide a fair indication whether or not you need this dose of vitamin D in supplements.