A bra can restrict lymphatic and interstitial fluid from circulating throughout the body and inhibits its very function of protecting the body from disease and cancer.

Take for example the elastic strap that is wrapped around your arm for a blood draw.  The purpose is to restrict blood flow and create back pressure on the veins.  Apply this principle to the bra and now you understand the impact a bra can have on the circulation.

Thermal imaging shows this effect: