Seasonality of thyrotoxicosis in Wellington

The month of diagnosis of hyperthyroidism in 183 patients from the area of Wellington, for the period 1977-1986 was ascertained. A significantly greater proportion of cases (58%, p less than 0.05) were diagnosed in the warmer period of the year (November to April) than in the cooler period (May to October). Although seasonal environmental factors, such as changes in iodine intake; or other unrecognised factors, such as differences among the patients themselves, may possibly play an aetiological or pathogenetic role, the significantly greater proportion of thyrotoxic patients diagnosed during the warmer 6-month period of the year is presently best explained by the fact that symptoms tend to be less tolerable in warm weather.