Forty is the optimal age for women to start having regular mammograms to reduce the number of breast cancer deaths, according to a US study.

Researchers in New York compared the commonly recommended mammograms schemes used in the US to estimate the most effective at reducing breast cancer mortality.

These included annual screening from when women turn 40; annual screening between the ages of 45 and 54, then every second year from 55 to 79; or every second year from 50 to 74.

According to the computer modelling, the first scheme reduced breast cancer deaths by an estimated 40 per cent, compared with 23 per cent and 31 per cent for the other schemes.