I'm a heart surgeon - this is the most crucial lifestyle change you need to make before you're 40

A heart surgeon has shared the most 'important lifestyle factor' to prioritize before turning 40, after admitting he 'personally struggles' with it.

Whether turning 40 seems a long way off or perhaps just around the corner, many doctors claim it's often around this age that the effects of years of poor lifestyle habits begin to catch up.

And speaking with UNILAD, Dr Jeremy London has shared the lifestyle factor you absolutely must prioritize, particularly as you move into your fifth decade of life.

"I believe sleep is the most important factor to prioritize, while smoking is the most important factor to avoid.

"If your sleep is off, it affects every other aspect of your life."

And while general guidance suggests adults need around 7-8 hours of sleep per night, the number of hours actually changes by age.

The doctor was very clear about what people should be avoiding. (@drjeremylondon/YouTube)

How much sleep do you really need based on your age?

According to the Centers for Disease Control and Prevention, experts say most healthy adults aged 18 to 60 should aim for at least seven hours of sleep each night.

Teenagers between 13 and 17, however, need slightly more, with eight to 10 hours recommended, while younger children require significantly longer to support their growth and development.

Newborns need the most sleep of all, with experts recommending between 14 and 17 hours a day, including naps.

How much sleep adults need (UNILAD)

Speaking in a video on his YouTube channel, Dr London added: "Don't trade sleep for other activities, and this is something that I personally struggle with.

"Recovery is so important throughout our lives, but it's really important when we get older."

What are the benefits of sleeping?

Getting enough sleep can have a major impact on your overall health, according to the CDC.

It often helps to prevent sickness, maintain a healthy weight, reduce stress and improve your mood.

But on a more serious note, it also supports heart health and metabolism, while lowering your risk of chronic conditions such as type 2 diabetes, heart disease, high blood pressure and stroke.

But the benefits don't stop there.

Prioritizing a good night's sleep comes with a wide range of health benefits. (Getty Stock Images)

On top of that, getting sufficient sleep can improve alertness, reducing the risk of motor vehicle crashes and related injuries or death.

What habits should people avoid regardless of age?

The doctor also highlighted two things people should absolutely steer clear of at any age.

"The first one would be alcohol," he said in the clip.

"If you really want to set the stage for yourself long-term, limit or remove alcohol - it's toxic to every cell in the body.

"I realize this can be hard because alcohol is everywhere, it is a personal choice. But just be thoughtful."

Next up, he says, is smoking and vaping.

"I don't think anybody would disagree that these are bad for you.

"It increases your risk of lung cancer, heart attack, and stroke. Don't vape, don't smoke."