Steve Redgrave on his battle with his weight and mood changes

But the most successful male rower in Olympic history (Redgrave won gold medals at five consecutive Olympic Games between 1984 and 2000) wasn't just feeling the effects of age.

A friend pointed out his symptoms could be due to low testosterone, and tests have since shown he has borderline testosterone deficiency.

"Since retiring from rowing, I've experienced unexplained weight gain particularly around my belly, tiredness, and feeling low and a bit depressed," reveals Redgrave, who turns 61 later this month.

"It was only after speaking with a friend that I learned these could be signs of testosterone deficiency, rather than just signs of getting older.

"Recent results show I have borderline testosterone deficiency. I'm working closely with my doctor to find a treatment that will work for me to overcome these symptoms, which may be testosterone replacement."

The father-of-three, who retired from rowing in 2000, had his levels checked by digital health company Ted's Health, which says testosterone deficiency can cause both physical and mental symptoms, including depression, fatigue and sexual dysfunction.

Low testosterone is also linked to type 2 diabetes (which Redgrave also has), with studies suggesting men who have low testosterone are four times more likely to develop it. Yet, many people are unaware of these links, or even what low testosterone is and how it can affect people.

"I've been a diabetic for 26 years and know a lot about it, but it wasn't until quite recently that a friend of mine told me about testosterone and how it can affect diabetes," says Redgrave, who has becoming an ambassador for Ted's Health to help raise awareness of low testosterone, and particularly the role in can play in the early stages of type 2 diabetes.

When Redgrave was diagnosed with diabetes in 1997, it was just a year after he'd won his fourth Olympic gold - and he was aiming to win his fifth at the 2000 Sydney Games.

"I was an athlete at the time, and I carried on competing for the next three years with diabetes," he recalls. "I was one of the fittest people in the country, and then you're told your body isn't doing what it was doing before. I honestly thought my rowing career would be over at that point, and it wasn't until I saw the specialist and he said he saw no reason why I couldn't carry on doing my sport.

"There are certain areas in life you can't follow when you're diabetic, but you can still achieve most of your dreams," he stresses.

Redgrave now has an insulin pump to help control his diabetes, and he puts his blood sugar levels in twice a day - compared with up to 10 times a day when he was competing. He says he eats what he wants "to a degree" these days, although it's certainly far less than the 6,000-7,000 calories per day he was consuming during his Olympics days.

He's also taking tablets to help improve his current health issues: "They're trying to help with the tiredness and weight, and trying to give me more enthusiasm."

He may also get testosterone support, which can either be through an injection which lasts for a few months, or by rubbing a gel onto the skin. "If I have to go down that avenue, I think I'll go for the injection, rather than a daily rub of gel - the injection would be a lot more convenient for me," he says.

He does still try to keep fit too - and has an extra-special reason to maintain his fitness now, he happily reveals.

"I generally try to keep fit - nothing compared to when I was an athlete, but I try to eat healthily and look after myself. My eldest daughter Natalie, who's a doctor, is pregnant, so I'm going to be a grandfather in July, and I want to be healthy and fit for the grandchildren that are going to start coming along from now," he shares.

"It's my first grandchild, and I'm looking forward to being a grandfather. But it makes me feel old!"

He admits he goes through different phases with fitness but says he's "in a pretty good phase at the moment" - exercising about three times a week, doing plenty of static biking in the gym and going out on the roads as the weather improves. He also tries to play golf at least once a week - "and the way I play golf is not a straight walk, so I get lots of steps in on those days!"

And what about rowing - does one of the world's best-ever rowers ever take to the water these days?

"Very rarely," he admits. "To me, rowing was an activity of competing, from when I went to my comprehensive school here in Marlow. I didn't really enjoy the training overly. But I enjoyed the success, and the harder you trained, the more success you had.

"For most people, it's about competing - even the people taking the sport up quite late. There's a whole circuit and races for almost any age group. Very few people do it as a leisurely activity, normally there's a goal at the end of it."

Redgrave admits he does miss the competition - "to a degree".

He adds: "I'm not very good at relaxing. I don't miss the amount of training we did, but I miss the camaraderie side. It's very much a team sport."

Sir Steve Redgrave is an ambassador for Teds Health (tedshealth.com)