Vitamin D is fat-soluble, which means your body has a hard time getting rid of it if you take too much. The Vitamin D Council recommends taking no more than the upper limit of 10,000 IU/day for adults, though some researchers consider this conservative. Signs of toxicity are low appetite, nausea, vomiting, thirst, excessive urination, weakness and nervousness.
The way that vitamins and minerals work in your body is interconnected. How well vitamin D works depends on the amount of other vitamins and minerals that are present in your body. The other vitamins and minerals needed to help vitamin D work well are called cofactors and, without these cofactors, supplementation can have undesirable effects. Vitamin D has a number of cofactors. According to the Vitamin D Council and others, the ones listed below are the most critical and should not be overlooked:
Most important for those of us who are hypothyroid, the symptoms of low vitamin D can look like low thyroid, such as fatigue and general aches and pains. Since vitamin D is critical for bone health, adequate levels may be necessary to prevent bone problems often associated with poor thyroid hormone replacement with T4-only. Plus, vitamin D levels (along with levels of iron and cortisol) need to be optimal for thyroid receptors to respond properly and for thyroid medications work properly.