Do not underestimate Ms Doris Teo's age or her petite 1.49m frame. The 53-year-old public servant has completed about 30 marathons in the past six years.

That is an average of five marathons a year. "Some years, I did seven or eight," she says.

Many of these races were run overseas, in cities such as Gold Coast in Australia, Tokyo in Japan and Chiang Mai in Thailand.

The avid runner has also finished in the top three in races held in Penang, Borneo and Hat Yai.

A sporty individual even before she became a marathon diehard, she took gym lessons and ran on the treadmill and outdoors.

She started to take running more seriously about 10 years ago, after taking part in a 10km race and enjoying the experience.

She and her husband subsequently joined a running group - and have since set up their own - to get to know kindred spirits and to get running tips from seasoned runners.

Her husband Lincoln Han, 47, teaches people how to appreciate and prepare Chinese tea.

They have a 26-year-old daughter, who recently graduated from Auckland University in New Zealand with a degree in marine science.

Like most runners, Ms Teo worked her way up from 10km races to half marathons and finally a first full marathon in 2011.

That year, she also ran her first overseas marathon, the Penang Bridge International Marathon.

The "addiction" to overseas marathons began after that, she says.

"It's very exciting. The route is new, the terrain is different and the entire environment is different too," she says.

Her favourite overseas marathons are the ones in Tokyo and Gold Coast, which she has participated in three and four times, respectively.

She likes that the Gold Coast Airport Marathon takes in Surfers Paradise, a busy waterfront area that has high-rise buildings next to a pristine beach.

The Tokyo Marathon has the best supporters, she says. Spectators along the race route hand out free snacks, such as bread, sushi, chocolates, biscuits and even sake.

"From the start of the race to the finish line, there are supporters every step of the way, cheering their hearts out, motivating and encouraging runners with cries of 'Gambatte!' (Japanese for 'Go for it')," she says.

Adding to the lively atmosphere are street performers singing, dancing and drumming.

She has various post-race must-dos in different cities. In Hong Kong, it is shopping and having dim sum. In Tokyo, it is a leisurely walk through the vibrant city's busy streets.

This year, she will tick off two more overseas races on her bucket list: the Berlin Marathon in Germany and the Auckland Marathon in New Zealand.

"It's nice to be able to go on these marathon holidays with friends and loved ones," she says.

"Completing a race as part of a holiday makes the trip so much more rewarding."