"I love the fact that we have a laugh on the show," she says. "I do think we've also managed to do a reasonable amount of good". Denise has been on the programme since its first broadcast in 1988, and has since replied to thousands of viewers' letters, offering comfort and advice to those who seek her help.
Here she talks about her most memorable moments, from dramatic phone-ins to emotional pleas in her postbag.
What was it like celebrating 25 years of This Morning?
It was heart-warming, but I was also quite proud, although it was a little weird looking at all those photos of myself throughout 25 years! The warmth of the crowd was wonderful. One mother asked me if I remembered meeting her little girl 25 years ago, then introduced me to her daughter, all grown-up! We had to give a résumé of what we remembered, and mine included spending nights out on the street with young people who were sleeping rough. Our viewers rose up in protest and we managed to affect the laws regarding young people receiving benefits.
Was there a particular moment where you felt the show's impact?
When I found the children in Africa and we were able to make their lives better. Two boys had been eating ants from the ground. I bought them some goats, thinking I'd just march the animals over, but ended up being dragged on my bum! We raised the money to build them a house and when I returned four years later, it was amazing to see the difference we'd been able to make. 800 children were sponsored by our viewers. They were fed, clothed, sent to school and now have better lives. That's the This Morning effect. I love the fact that we have a laugh on the show, but I do think we've also managed to do a reasonable amount of good.
How do This Morning viewers respond to the show?
There's a very personal side to being on This Morning. In 25 years, a lot happens to you. I've been widowed, married again and lost a son. The viewers fold themselves around you. When my son died, I was really touched by the letters I received from viewers. The audience is utterly amazing. I remember a dramatic phone-in with a woman who was locked in her room by her abusive partner. It was probably one of the defining moments of This Morning and we had so many people offering to help to find her and opening their homes to her.
Is there a question you get asked the most from people?
"Are Phillip and Holly as lovely as they seem?". I can hand on heart say that they're lovely to work with. Phillip and Fern were there when my son died and I would not have been able to go back to work without them. As for Holly… if I had a daughter, I would want her to be exactly like Holly.
Do people come up to you and tell you their personal problems?
My husband once joked that when he's with me, the supermarket run is four times longer than it needs to be. Almost every conversation or letter begins with, "I know I really haven't got a problem compared with the ones you get, but…" and then they tell you something that's a huge problem. They just feel self-conscious asking for help.
Do you hear from people after you've helped them and see the happy ending?
That's one of the nicest parts of the job. I'll open a letter and it will be a snap of a new-born baby from someone who was struggling to get pregnant. Sometimes I worry because we can't always provide a listening ear, like when we did the Christmas bonanza. I told the editor I was worried and we decided that I would stop halfway through the show and acknowledge that not everyone would have a merry Christmas. It's become a tradition, and what I'm trying to tell people is that it may be bad now, but there is a new year.
Have you noticed a difference in problems over the years?
Human nature hasn't changed and I don't think it ever will, so core problems never change. The huge difference comes with the internet. I do love it, but at the same time it's increased the numbers of people who are now finding out about infidelity. Half the nation is checking its partner's mobile phones. It's made a huge difference to an agony aunt's postbags.
Do you think there's the same number of affairs, or that it's just made it easier to have one?
I think there's been an increase because there is less of a taboo about it. I don't think there's been a huge shift, I just think we're just more open about it. Infidelity has always existed – even the Romans did it! Across all the years of being an agony aunt, I don't think I've seen a huge change in human nature, but modern technology has made a difference. We're less afraid of consequences.
Who do you turn to when you have a problem?
The truth is that I'm not very good at turning to anybody. I know my own shortcomings in that direction, but I do tend to keep things to myself. I'm afraid it's not quite a "Do as I say and say as I do" situation.
Do you get emotional on screen?
I'm not as bad as I used to be but I am sometimes affected. For example, after I had my first grandchild, we had a caller phoning in to say she wasn't allowed to see her grandchildren and I immediately really felt for her. I'm definitely better though, I'm not such a cry baby as I was at the beginning!
Are there times when things stay with you after you've spoken to callers?
Of course, you get involved because you throw yourself so much into the business of solving things. I find the letters from people who know they're going to lose someone they love are very hard to answer. You can feel very down about your own life, then you open the letters and realise how lucky you are, because there's so many people in so much more trouble than you're in.
What are the certain types of questions you get at the beginning of a new year?
It's 50/50. Half the nation looks at the new year as a chance to move forward, whilst the other half say, "last year was awful, this year will be worse". At the start of the year I did 'divorce week' because a lot of people think, "I'll get Christmas over for the kids and then I'll grasp the problem by the throat".
Do you think that everyone re-evaluates their lives in the New Year?
I think that in emotional terms, last year was a hard year for the majority of people. As a country, it was a tough year, and what's happening in the country is reflected in the postbag. So I'm quite optimistic for this year, purely on the basis that it can't be as bad as last year. I'm hoping for a lighter postbag and more good cheer. Let's hope I'm right.
Catch Denise on This Morning, weekdays, 10.30am on ITV. To vote for This Morning in the National Television Award's visit www.nationaltvawards.com