Doctors are being urged to check for signs of dementia or heart disease in hip implant patients.
There are concerns that the metal-on-metal devices are leaching toxic chemicals into the blood which cause serious health complications.
The Medicines and Healthcare products Regulatory Agency announced last month that patients would be called in for x-rays and blood tests to check for adverse reactions.
Now a spokesman for the watchdog said it was also keeping a 'weather eye' on a possible link to heart attacks and dementia.
Dr Neil McGuire, clinical director of medical devices at the MHRA, said he wanted to establish whether cobalt leached from the implants was causing adverse effects.
Patients with the 'metal on metal' hip implants will be advised to have X-rays and undergo blood tests due to fears of their toxicity