Drinking from plastic water bottles, or taking "The Pill" can cause hypothyroidism by raising levels of estrogen hormone in your body. The same can be said about menopause drugs which contain the same synthetic estrogen ingredients or commercial cattle injected with estrogen hormones to make animals heavier at the point of sale. In humans, these hormones raise estrogen, and estrogen holds fat. This sounds counter-intuitive, but men frequently have high levels of estrogen, especially if they have prostate problems but that's another article. My point is excess estrogen causes too many transporters, or taxis which bind up your active thyroid hormone. When bound like that, thyroid hormone is completely unavailable to your cells which is where you need it.