A comparison of the incidence of the different histological types of thyroid carcinoma in an area of high dietary iodide and an area of normal iodide intake has been made. The areas chosen were Iceland and the region of Northeast Scotland centred on Aberdeen; both areas have clearly defined populations served by a single pathology laboratory. All definite and dubious thyroid carcinomas from both regions were examined and classified by the same two pathologists. The age-specific incidence rates for papillary carcinoma in surgical specimens in both areas rose with age; they were five times higher in Iceland (high iodide area) than in Northeast Scotland. The numbers of follicular carcinomas were small, and this tumor was relatively less frequent in Iceland than Aberdeen. These findings, together with the known high relative frequency of follicular carcinoma and low frequency of papillary carcinoma in areas of endemic goitre, lead to the suggestion that the incidence of papillary carcinoma and follicular carcinoma are separately influenced by dietary iodide, papillary carcinoma being high in areas of high iodide intake and low in areas with low dietary iodide. No evidence to implicate lymphocytic thyroiditis, radiation or genetic factors in the genesis of thyroid carcinoma in Iceland or Northeast Scotland was found in this study. Undifferentiated carcinoma was about three times as common in Iceland as in Northeast Scotland. Malignant lymphoma of the thyroid was suprisingly common in Northeast Scotland, possibly related to the high frequency of thyroiditis found in this region. These studies suggest that the incidence of different histological types of thyroid malignancy is influenced by different etiological factors. They also provide support for the subdivision of thyroid malignancy into these different types, and for the general importance of accurate histological typing in cancer epidemiology.

1. A study was undertaken to examine the effect of supplementation of diets with fats of different chain length and degree of unsaturation on the performance, carcase characteristics and tissue fatty acid composition of broilers. 2. Three hundred and sixty 19-day-old female broilers were fed on diets containing supplemental fat/oil (50 g/kg) in the form of beef tallow (BT) (diet T-T), soyabean oil (SBO) (diet S-S), rapeseed oil (RSO) (diet R-R), marine oil (MO) (diet M-M) or binary mixtures (0.5:0.5 w/w) of these lipids (diets T-S, T-R, T-M, S-R, S-M, and R-M) to 54 d of age. Food intake, live weight, plucked weight and the lipid concentration and fatty acid composition of abdominal fat pad, liver and breast muscle were measured. 3. Food intake, plucked weight and live weight were greatest for diet T-T and lowest for diet R-R. Food conversion ratio was poorest for birds fed on diets containing BT. Lipid concentration in abdominal fat pad was significantly higher in birds fed on diets containing SBO. Liver lipid concentration was significantly reduced by diets containing RSO. 4. Abdominal fat pad fatty acid profile was most readily altered by dietary fatty acids. There was a strong correlation between dietary fatty acid composition and tissue fatty acid composition for all fatty acids except C14:0, C20:0, C20: 2n-6 and C20: 4n-6. The tissue P/S ratio ranged from 0.40 for diet T-T to 1.40 for diet S-S. The n-6/n-3 ratio was significantly increased by the inclusion of SBO and decreased by the inclusion of MO. 5. Liver fatty acid profile was least modified by dietary fatty acids. There was an inverse relationship between liver and dietary C20:4n-6 concentration. Tissue C18:2n-6 and C20:4n-6 were highly correlated, suggesting significant interconversion by delta-6 desaturase in this tissue. The n-6/n-3 ratio was significantly increased by inclusion of SBO and significantly decreased by the inclusion of MO. 6. In breast muscle MO-based diets increased the proportion of n-3 PUFA at the expense of n-6 PUFA. The tissue concentrations of C18:1n-9, C18:2n-6, C20:1n-9, C20:5n-3, C22:5n-3 and C22:6n-3 were strongly correlated with dietary fatty acid composition. Muscle and diet P/S and n-6/n-3 ratios were highly correlated.

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