This study is from before iodine was added supplementally (1924 in the US). You are correct that iodine deficiency leads to low body temperature due to hyperth

This study is from before iodine was added supplementally (1924 in the US). You are correct that iodine deficiency leads to low body temperature due to hyperthyroidism. Dairy and grain are the biggest sources of iodine. To get your iodine from salt alone would require over 3 grams per day, which is quite a lot. The average American consumes 3.4 g, DV recommendation is 2.3 g.