“…Some studies have not observed the effect of PCBs on TSH [ 339 , 340 , 341 , 342 , 343 , 344 , 345 , 346 , 347 , 348 , 349 ] and thyroid hormone levels [ 339 , 340 , 341 , 348 , 350 ]. However, other studies have shown an increase [ 351 ] and a decrease [ 352 , 353 ] in TSH, an increase [ 347 , 353 ] and a decrease [ 344 , 346 , 351 , 352 , 354 ] in T3 and an increase [ 342 , 347 , 349 , 353 ] and a decrease [ 343 , 346 , 351 , 352 , 354 , 355 , 356 ] in T4 after exposure to PCBs. Although previous studies have investigated the effect of PBBs on the development of thyroid diseases [ 357 , 358 ], we have found only one study investigating the effect of PBBs on TSH and thyroid hormone levels in euthyroid individuals [ 349 ].…”