Too little thyroid hormone, and the individual tends to feel mentally sluggish, while too much induces anxiety and nervousness. Normal reproductive behavior and physiology is dependent on having essentially normal levels of thyroid hormone. Hypothyroidism in particular is commonly associated with infertility. Thyroid Disease States Disease is associated with both inadequate production and overproduction of thyroid hormones. Both types of disease are relatively common afflictions of man and animals.
Hypothyroidism is the result from any condition that results in thyroid hormone deficiency.
Historically, this problem was seen particularly in areas with iodine-deficient soils, and frank iodine deficiency has been virtually eliminated by iodine supplementation of salt. Inflammatory diseases of the thyroid that destroy parts of the gland are clearly an important cause of hypothyroidism. Common symptoms of hypothyroidism arising after early childhood include lethargy, fatigue, cold-intolerance, weakness, hair loss and reproductive failure. If these signs are severe, the clinical condition is called myxedema . In the case of iodide deficiency, the thyroid becomes inordinantly large and is called a goiter .