Changes in Heart Rate
The hormone produced by the thyroid gland determines how fast or slow your heartbeats. Excessive amounts of the mineral can speed up your heart rate to beat faster than normal, while insufficient amounts can cause it to beat dangerously slow.
Normal heartbeat should range between 60 to 100 beats per minute. Athletes may be excused for a higher rate due to the nature of their work.
When the heart rate is too fast, it may not pump enough blood to reach all the organs, causing shortness of breath or lightheadedness. When the heart rate is too slow, It could cause weakness, fatigue, dizziness, and fainting.