Your body makes its own vitamin D and you also get it from dairy sources and supplementation. Vitamin D stimulates your bones to absorb calcium and also helps control your blood pressure. Synthroid is a synthetic form of the thyroid hormone prescribed for a condition known as hypothyroidism. Individuals with hypothyroidism may also exhibit lower than normal vitamin D levels, according to Theodore C. Friedman, M.D., Ph. D., author of "Vitamin D Deficiency and Thyroid Disease." Current literature shows no adverse interactions between synthroid and vitamin D; however, because you are taking a prescription medication, take precautions when taking other drugs, supplements or vitamins.
Consult your endocrinologist before starting your vitamin D regimen. Your endocrinologist can advise you of any precautions you should take regarding combining the vitamin D with your synthroid.
Take your synthroid per your endocrinologist's instructions. Your doctor may prescribe one daily dose or multiple doses spread throughout the day.
Take at least 1,000 IU of vitamin D daily, unless your physician directs otherwise. The maximum safe dosage, or tolerable upper intake level, is 4,000 IU.
Work with your doctor to monitor your thyroid function and serum vitamin D levels. Your doctor may make adjustments to your synthroid or vitamin D dosage, if necessary.
Consult your physician immediately if your hypothyroidism symptoms worsen, such as sensitivity to cold, fatigue and joint pain as well as depression, constipation and muscle weakness.