Rachel O’Brien has the choice to be healthy. She realized that during her first triathlon four years ago.

She and her fellow athletes in the Danskin Women’s Triathlon Series were cresting what they call “Killer Hill” when she saw one of her patients from Overlake Cancer Center sitting atop the hill, cheering them on. The young girl was using an umbrella to shield her bald head from the sun.

“I realized at that point that people who have cancer don’t have a choice,” says O’Brien, 26, of Renton. “But I have the choice — to be healthy, to lose weight. I chose to live, basically.”

That’s also when O’Brien chose to do another triathlon. And another, and another. She competes in her 15th running, swimming and biking event Sunday. It will be her fourth Danskin triathlon, in Seattle.

“I’m hooked,” she says.

O’Brien is a worship coordinator at New Life Church in Renton. She is the former receptionist at Overlake Cancer Center.

She did six triathlons last summer but cut back to four this year to allow her body enough recovery time.

O’Brien starts “intensely training” for triathlon season in February or March. That means double workouts, like swimming half a mile and going for a bike ride in the morning and going for another bike ride and a run at night.

“I love swimming and I love bike riding,” O’Brien says. “Running is my weakest point; I don’t enjoy it. But I’m trying to get better at that. My goal this season is to run more.”

O’Brien’s Danskin goal is to beat her previous time. She’s aiming for 1 hour, 40 seconds. Her first time four years ago was 2:35.

O’Brien’s former coworkers had to to talk her into that first triathlon. She weighed nearly 300 pounds then and had never taken a swimming lesson.

“I thought no way could I do that,” she recalls.

But she decided to go for it. She taught herself to swim and finished the race.

She has lost 70 pounds since then, and isn’t finished yet.

“I feel like I’m in the middle of my story,” she says. “I’ve lost 70 pounds and have 70 more to go.”

She also hopes to work up to an Olympic triathlon, which at nearly 32 miles, is about double the length of the 16-mile sprint triathlon.

O’Brien started triathlons as a way to lose weight. But she fell in love with the competition.

“It’s a part of my life and will be forever,” she says.

But training and competing is still a struggle.

“Pretty much every time I start I’m like, ‘Oh my gosh, did I start this again?’” she says. “But once I cross the finish line I’m like, ‘Oh my gosh.’ It’s the best feeling in the world, it really is.”

Danskin triathlon

The Danskin Women’s Triathlon Series hits Seattle Sunday. The event is open to women ages 14 and up. Five percent of all entry fees go to Breast Cancer Research Foundation and all funds raised by participants goes to the Breast Cancer Research Foundation and the National Association of Team Survivor, a nonprofit benefiting women with a present or past cancer diagnosis. For more information about the Danskin triathlon, visit www.danskin.com/triathlon.html