Good evidence on the safety of silicone gel breast implants is still lacking, almost 10 years after they were reintroduced to the US market, a review has warned.

Flaws in past research have hampered results, and as such it is difficult to say whether any true links exist between the implants and serious health conditions.

Dr Ethan Balk, of the Brown University School of Public Health in Providence, Rhode Island, said: 'Owing to inconsistencies among the studies reviewed, further investigation is required to determine whether any true associations exist between silicone gel implants and long-term health outcomes.'

Breast enlargement was the most commonly performed cosmetic surgery in the US during 2014, with more than 286,000 women having the procedure, according to the American Society of Plastic Surgeons.

Silicone implants are used in around three quarters of those surgeries. 

Unlike implants that are filled with saline, silicone implants are filled with gel to look and feel more like natural breasts.

The US Food and Drug Administration (FDA) stopped the sale of silicone gel implants in 1992, in response to public concern.

But the implants were reintroduced in 2006.

Conducting the new analysis, researchers reviewed more than 5,000 studies of health outcomes after breast implant surgery.

Thirty-two of the studies met their criteria for inclusion in the new report. 

The studies, which came from North America, Europe and Australia, reported on women who received breast implants between 1964 and 2003. 

Researchers were interested in possible links between silicone gel implants and several types of cancers, connective tissue diseases, rheumatoid arthritis, immune system disorders, blood flow problems, reproductive issues and mental health. 

For most outcomes, however, 'there was at most only a single adequately (done) study', and the researchers could not find enough evidence to link breast implants to any health conditions. 

'Furthermore, because most studies analysed all breast implants, their findings are not specific to silicone gel implants,' the authors reported.

There was a suggestion that breast implants are linked to a decreased risk of breast and endometrial cancers, and that implants were tied to an increased risk of lung cancer, immune system disorders and blood flow problems.

The researchers say larger studies may be able to overcome the gap in the evidence, if the authors of those studies could re-analyse their results to tease out the data that are specific to silicone gel implants, and account for variables like family medical history, hormone use, weight, depression and substance use. 

This new analysis is meant to support the creation of a national breast implant registry from the American Society of Plastic Surgeons and the FDA, which will track all breast implants, the researchers wrote.

The review was published in the Annals of Internal Medicine.