Can one alcoholic drink be enough to wreck your sleep?

An NHS survey reports that 55% of men and 42% of women drink alcohol at least once a week.

And many people incorporate an alcoholic drink into their evening routine - known as a "nightcap."

Gary Brecka, a human biologist and longevity expert, says: "Even one drink close to bedtime interrupts your sleep, and it isn't really the alcohol that does it, it's what the alcohol becomes."

He warns that the notion of a "nightcap" can be more damaging than people think.

"Your liver converts it into a compound called acetaldehyde, a toxin that your body, and your brain, then have to process while you are trying to rest," says Gary, who spent 20 years researching mortality science and identified sleep as one of the biggest variabilities in life expectancy.

And there's a reason you wake up in your sleep after a night drinking.

"Alcohol also converts to sugar while you sleep," Gary, host of The Ultimate Human podcast, explains.

"Your blood sugar climbs, almost like having a candy bar in your sleep, and rising glucose pulls you back towards a waking state."

So despite the initial sedative effect, you're unlikely to get clean, deep sleep. And this has a knock-on effect on both your physical and mental health.

"Physically... alcohol dehydrates you, it burns through the glutathione your body needs to recover, and it makes your liver process a toxin every time."

Glutathione is a natural antioxidant produced by the liver that breaks down toxins and supports the immune system.

"Do that regularly and you feel it in your energy, your skin and your recovery. Mentally, the bigger cost is usually the sleep you lost.

"Poor sleep leaves you more emotionally reactive and less able to think clearly the next day," he explains.

"So the drink you had to take the edge off can leave you more wound up, not less."

Over time, sleep deprivation can build up, the expert warns.

"One nightcap feels harmless. But deep sleep is when your brain runs its own overnight clean-up and clears out waste, and alcohol trades that repair time for processing time, every time you drink.

"Even one night of poor sleep has been shown to raise waste levels in the brain."

Because of this, he believes a regular drink before bed is not a treat you get away with, and the cumulative effect can be dangerous.

Current health guidance says you should be drinking no more than 14 units a week - which roughly equates to four to five glasses of wine, or four to six pints (depending on strength).