I posted this earlier in another discussion where members were asking questions about boron.

This article provides a great overview of evidence. "Boron supplementation cannot be recommended on the basis of current research. Its basic role in metabolism of bone and the reproductive system remains unclear."
– Boron Supplementation for Low Bone Density and Osteoarthritis (2002) https://www.reliasmedia.com/articles/118545-boron-supplementation-for-low-bone-density-and-osteoarthritis

More recent info here:
– Brains, Bones, and Boron https://www.healthline.com/health/brains-bones-boron
"While boron supplements have been considered as a possible treatment for people with arthritis, more clinical evidence is needed to support this claim.
Boron is considered safe for most people, but large amounts can be harmful. There also isn’t data regarding a safe level for children younger than 1 year old. Its safety hasn’t been studied in pregnant women.
It’s important that you talk with your doctor before taking supplements. It’s unlikely that boron supplements are necessary. Most experts recommend increasing intake through dietary sources like fruits and vegetables before considering supplements.
If you don’t want to take additional boron supplements, eating foods that contain boron, like prunes, raisins, dried apricots, or avocados, can help increase boron levels."

– NIH Medline Plus: Boron https://medlineplus.gov/druginfo/natural/894.html
"When taken by mouth: Boron is LIKELY SAFE when taken by mouth in doses that don't exceed 20 mg per day. Boron is POSSIBLY UNSAFE when taken by mouth in higher doses. There is some concern that doses over 20 mg per day might harm a man's ability to father a child. Large quantities of boron can also cause poisoning. Signs of poisoning include skin inflammation and peeling, irritability, tremors, convulsions, weakness, headaches, depression, diarrhea, vomiting, and other symptoms."
"Hormone-sensitive condition such as breast cancer, uterine cancer, ovarian cancer, endometriosis, or uterine fibroids: Boron might act like estrogen. If you have any condition that might be made worse by exposure to estrogen, avoid supplemental boron or high amounts of boron from foods."

As always, please consult with your medical provider before taking supplements.