Thyroid disease is usually diagnosed by testing levels of thyroid stimulating hormone (TSH) and thyroxine (T4) in the blood. Each laboratory will have a slightly different range of normal levels but your doctor will know how to interpret the results.
The thyroid hormone affects multiple organs and systems in the body. Because it is such an important hormone, disruption in thyroid levels can affect many physiological aspects of a person. This includes breathing, heart rate, muscle strength, cholesterol levels, body temperature, and many more. Overactive thyroid or hyperthyroidism does more than make you feel uncomfortable or lose weight. The thyroid hormone is involved in the body’s metabolism, or energy production and usage. When hyperthyroidism affects the heart, it leads to irregular heartbeats (or arrhythmia). This irregularity can lead to pain in the chest area (angina); heart failure and more. Increased heart pumping due to hyperthyroidism causes the heart to swell and there can be up to a 250%increase in heart output – this is 2.5 times more blood pumped across the heart each day! Increased heart output can also lead to high blood pressure. The increased workload on the heart increases the size of the heart which then leads to impaired relaxation of the heart. In the long term, hyperthyroidism is linked to a 16% increased risk of heart and blood vessel (cardiovascular) disease.
Conversely, an underactive thyroid or hypothyroidism is slightly less common, affecting an estimated 2.1% of Malaysians. Someone with less thyroid hormone than normal may experience dizziness, fainting, fluid retention around the heart (pericardial effusion) and surprisingly, high blood cholesterol. The reason for increased cholesterol levels in someone with hypothyroidism is thyroid controls cholesterol and fat metabolism. Therefore, any lowering of thyroid levels results in poorer control of fat metabolism. Persons with hypothyroidism also have a slower heart rate and increased stiffness of their blood vessels. Someone with hypothyroidism often complains of breathlessness upon exertion eg, climbing the stairs or a long walk. Weight gain is also a common side effect.
The reason blood pressure goes up with hyperthyroidism is due to the increased pumping of the heart, which in turn increases pressure in the blood vessels. The most common cause of a stroke in hyperthyroidism is irregular heart rhythm, which can cause an ischaemic stroke – blood clots formed in the heart go to the brain via blood vessels and block the finer blood vessels in the brain.
WORDS | HealthToday | Pank Jit Sin