I've heard that being overweight can damage the thyroid, but not from reputable sources. I chalked it up to urban legend, but then I read this article and thought "maybe."
http://howtoloseweightreallyfast.com...thyroid-damage
It wouldn't surprise me, but without more evidence, I'd consider it a "maybe" at most.
Quite a few of the obesity-related disorders are both chicken AND egg. The condition puts you at risk for obesity, and the obesity worsens or puts you at risk for the condition. Some people may gain weight after acquring the condition, and some people acquire the condition after becoming obese - and the obesity worsens the condition and the worsening of the condition worsens the obesity in an endless downward spiral.
Osteoarthritis is just one of these type of conditions. If a thin person has osteoarthritis, they may move less (because of the pain and stiffness) and if they don't reduce their calorie intake, they may gain weight. The weight gain puts more stress on the joints and damages the joints further. The person moves even less and gains even more weight.
Or a person may develop arthritis as a result of obesity. Either way, it's not so much a chicken and egg question as a snowball question. One feeds the other, and together they snowball. The progression of one, feeds the progression of the other
Diabetes, insulin resistance, hormonal and metabolic function, high blood pressure, heart disease, inflammatory disorders, some digestive disorders, sleep apnea, and possibly even autoimmune disorders may all fall into the snowballing category with obesity. It becomes a matter of trying to break or at least slow the snowballing cycle.
I have a borderline low thyroid condition, insulin resistance, autoimmun and inflammatory issues, osteoarthritis... I had sleep apnea. Addressing the sleep apnea (by means of a cpap) resulted in weight loss (without trying) and losing the weight (and more by my own effort) resulted in the sleep apnea disappearing.
In the scheme of things, I'm not sure that it really matters how you get into the snowball. Getting out of it, or slowing its speed is all any of us are left with (at least until we're better at recognizing, avoiding, and treating/preventing the snowballs in the first place).