Iodine intake and the seasonal incidence of thyrotoxicosis in New Zealand.
We explored a possible relationship between the seasonal variation in the incidence of thyrotoxicosis in our area and iodine intake, as assessed by measuring the 24-h urinary iodide excretion rate eight times at 3-month intervals in a group of normal subjects and in 992 outpatient specimens over a 2-year period (1988-1990). For the period 1978-1990, 139 cases of thyrotoxicosis were diagnosed during the warmer half of the year (November-April) and 100 cases during the cooler half (May-October). This difference was statistically highly significant (P = 0.013). A similar disproportionality in the incidence of thyrotoxicosis was observed between the warmer (57%) and cooler (43%) halves of the year for the period 1988-1990. During the 1988-1990 period there was no discernible seasonal variation in either the milk iodide concentration or in the cumulative mean 24-h urinary iodide excretion rates for the normal subjects or the outpatients. We conclude that the higher proportion of thyrotoxic patients diagnosed during the warmer 6-month period of the year in our area is best explained by the fact that symptoms tend to be less tolerable in warm weather. A comparison of our findings on 24-h urinary iodide excretion rates with data collected in our area 25 years ago suggested that iodine intake may have declined.
Ford
H C
HC
Department of Pathology, Wellington School of Medicine, New Zealand.
Johnson
L A
LA
Feek
C M
CM
Newton
J D
JD
D000328:Adult; D000818:Animals; D004032:Diet / Q000009:adverse effects; D005260:Female; D006801:Humans; D007454:Iodides / Q000032:analysis / Q000652:urine; D007455:Iodine / Q000008:administration & dosage / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D008892:Milk / Q000737:chemistry; D009520:New Zealand / Q000453:epidemiology; D012621:Seasons; D013696:Temperature; D013971:Thyrotoxicosis / Q000139:chemically induced* / Q000453:epidemiology / Q000652:urine
D007454:Iodides; D007455:Iodine