Prevalence of thyroid disease
In Canada thyroid disorders are estimated to affect one in twenty. Most thyroid disorders are 57 times more common in women. 13 million Americans have a thyroid disorder and more than half of them are not aware of it. The distribution of Graves` Disease around the globe, so far as data is available, appears to be relatively equal, affecting all countries and races. Although Graves` Disease most frequently occurs in women in the middle decades between 30 and 60 yrs (eight times greater in women than in men), it also occurs in children and in the elderly. Severe thyroid eye disease occurs in possibly only 525% with an overactive thyoid. Smoking increases the risk nearly 8 fold. The risk is worse in males, older women and in those with severe overactive thyroid conditions. Mild thyroid eye disease can occur in many more patients (up to 75% or more).
Aside from the infrequent occurrence of postnatal thyrotoxicosis due to maternal antibodies, the incidence of spontaneous Graves` Disease in children before the age of ten is most unusual, but the incidence climbs with each decade until about age 60. The greater incidence in women is typical of most thyroid diseases including multinodular goiter and differentiated thyroid carcinoma. The mechanism for this association is unknown. One possibility is that female reproductive activity somehow stresses the thyroid. Another possibility is that the promoter for certain genes such as Class II HLA molecules may have estrogen receptor response elements and thus be activated more easily in women. The well known familial distribution of Graves` Disease recognized by all clinicians caring for patients is thought to be explained by inheritance of specific genes, as detailed previously.
Thus several elements may contribute to the development of Graves` Disease. There is a genetic predisposition to autoimmune disorders. Infections and stress may play a part, so Graves` Disease may have its onset after a severe external stressor. In other instances, it may follow a viral infection or pregnancy. Most often the exact cause of Graves` Disease is not known. It is not contagious, although it shows a tendency to run in families and is associated with other so-called autoimmune conditions.
Incidence and distribution of Graves` Disease
The incidence of Graves` Disease in Olmstead County, Maryland (USA) was found to be 30 cases per 100,000 population annually. A thorough examination of an English town by Tunbridge and associates found an incidence of 100200 cases per 100,000 per year, significantly higher than the previous estimates. In this report, it was also found that 2.7% of women and 0.23% of men had either current Graves` disease or a history of Graves` disease. This survey also noted that goiter was present in 15% of women, antithyroid antibodies in 10.3% of women, and that hypothyroidism was about two-thirds as common as Graves` disease. A recent update in this area showed a continuing incidence of 80 cases/100,000 women/year. Data attest to a lifelong incidence of autoimmune thyroid disease of > 6%, comprised roughly equally by Graves` disease, Hashimoto`s thyroiditis and idiopathic hypothyroidism.