Doha, Oct 1 (AFP) After battling an auto-immune disease for the past two years, Grenada's Kirani James is simply happy to be back on track at the World Championships.

The 2012 Olympic gold medallist breezed through his 400m heat at the Khalifa Stadium in Doha on Tuesday in what was only his fifth race since being diagnosed with Graves' disease in 2017.

The 27-year-old qualified for the semi-finals with the fastest time of the opening round, a brisk 44.94sec.

In April 2017, James was left slumped on the track at the Drake Relays in Iowa, barely able to summon any energy because of a mystery illness which had caused him to lose weight at an alarming rate.

Tests revealed he had Graves' disease, a condition that causes the thyroid to overproduce thyroxine, a hormone that accelerates the metabolism.

"It makes you lose a lot of weight, leaves you with no energy," James said Tuesday.

James has drawn inspiration from US sprinting legend Gail Devers, who overcame the same condition to become a two-time Olympic champion.

"When I got diagnosed, my coach said 'I remember Gail Devers had something like that'," James said. "So if she came back, we knew we could just follow a plan and get back.

"It took Gail two years to get back. I'm still on that two-year cycle, but I feel a lot better now than I did two years ago."

James treats the condition with medication that stablishes the levels of thyroxine in his bloodstream.

"It's not really a cure. I have to be on lifetime medication to kill off the thyroid, that takes it from over-producing thyroxine to zero. It takes a while for the medication to balance it out.

"If I wasn't on the medication, if it was at zero, I'd gain a lot of weight, be out of breath."

James, who himself exploded onto the scene to win the 2012 London Olympics as a teenager, said he is now getting used to the changed landscape of his event.

"I've been away for two years," he said. "I'm looking at the start lists and seeing names and saying 'Who's this guy? Who's this guy?'

"That's the beauty of our event. It's so volatile. Every two years you see new guys come along. That's why I like it.

"The challenge is to stay consistent, because there's so many guys coming through." One of those new guys is Michael Norman of the United States, who has lit up the 400m this year with a world best mark of 43.45sec in his first season.

Norman won his heat with the second-quickest time of the round, 45 flat. AFP SSC

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