A Victorian couple aged in their 60s have begun their challenge to run a marathon every day of this year.

Grandparents Alan Murray and Janette Murray-Wakelin are running together around Australia, and set off this morning from the heart of Melbourne.

They will spend tonight in Berwick, south-east of Melbourne, before running to Gippsland via the Princes Highway.

The pair want to raise money for charities by running 365 marathons in 365 days.

If successful, they will have covered about 15,500 kilometres by the end of the year.

At 52, Mrs Murray-Wakelin was diagnosed with breast cancer and given a prognosis of six to 12 months to live.

She decided against conventional treatment and has consumed raw food ever since.

Mrs Murray-Wakelin says she hopes the couple's marathon effort will inspire people to make healthy choices.

"I think with our age that's something that will inspire people to realise it's never too late to make changes and to think more consciously about what they're doing so that they're healthier, and get younger every year instead of getting older," she said.

"For us, we think about the food that we eat so that we're healthy, and just our lifestyle being a healthy lifestyle."