Hair breaking off, thinning and getting shorter seemingly out-of-the-blue is what led me to visit my doctor, who did a blood (hemoglobin) test and discovered I was anemic. Although I knew nothing about hair care at the time, this has nothing to do with hair care. It's about getting red blood cells to the scalp and roots (and throughout the body) to nourish them.
The doctor recommended iron supplements and the breakage stopped in its tracks literally within days. I went directly from the doctor to a nutritionist who made sure I understood to take iron at the same time as vitamin C, which helps the body absorb the iron.
BTW, I learned I have been anemic all of my life but it wasn't until a few years as an adult that this iron deficiency abruptly affected my hair.
For the ladies reading this--please don't start popping iron supplements without getting tested by the doctor first to see if you need them. Iron is toxic if your body doesn't need more.