I’LL admit it. When speaking in public and on a subject I feel passionate about – and yes, there are plenty – I can lose track of time. Or as the less charitable might put it, go on a bit.

So I am not offended when I see someone in the audience stifling a yawn. I just take it as a hurry-up call, in contrast to some of my old teachers who saw yawning as a sign of open rebellion.

I wasn’t annoyed – just worried –when I was met with an outbreak of yawning when I went to visit a school a while back.

It was at Macmillan College, Middlesbrough, and I was there with our Director of Public Health, Edward Kunonga, for their induction course for new students from the feeder primary schools.

The focus for the three days was how to stay healthy. It was brilliantly done and a real credit to the school. But on the final day when we all met up to discuss what we had learned, I was genuinely puzzled by the number of young people who were yawning and looking dead beat.

As I said to Edward afterwards, it wasn’t boredom that was making them nod off, it was plain and simple tiredness.

So I was interested this week to read some research that has concluded that more than half of all teenagers are sleep deprived.

The findings come from, Russell Foster, Professor of Circadian Neuroscience at Oxford University, and while you might say this is just another ivory tower academic stating the obvious, I think his research is well worth studying.

Hormonal changes in teenagers, the professor has concluded, effectively programme them to get up and go to bed late. But added to the natural turmoil of growing up, the modern adolescent has at his or her fingertips a whole array of computers, TVs, mobile phones all primed to provide mental stimulus exactly when they should be winding down.

Tired teenagers do less well at school. They make the wrong choices about food, going for the high fat, high sugar junk that gives them a quick lift, rather than solid nutrition. And, as we all know, they can be murder to live with.

Teenagers should get around nine hours sleep. That’s to be taken nightly, of course, not as we’ve all seen by lying comatose for 36 hours after three days and nights of non-stop partying. Getting teenagers to see things like this is quite a battle though.

After our visit to the school, I asked Edward to ensure that we gave sleep just as much attention as healthy eating and exercise in our public health strategy. Schools and colleges are more clued up and alert to the issue than ever before.

It is another example of how the key to good health isn’t fancy diets or magic pills.

It is based on simple commonsense solutions that require, not a lot of money, but quite a bit of self-discipline. Maybe that’s why we’re so reluctant to follow them.

When you’re a teenager you think you’re invincible. Pushing yourself to the limit is part of growing up. But when I see what some young people put themselves through, I shudder. If someone was forcing them to act like that they’d be done for cruelty.

So next time, you hear the cry “just another five minutes”, as you demand lights out maybe it’s time for one of those talks that all parents and teenagers dread, but which we all have to have. Whatever they’re doing will still be there in the morning and will probably look better after a good night’s sleep.