Q. My husband stays up late and gets by on just four or five hours’ sleep. Is that enough?

Lisa Artis of The Sleep Charity is here to help.

While there is no magic number for how much sleep we should get, there is a general consensus that around seven to eight hours is best.

Experts believe that most adults require somewhere between six and nine hours in order to feel refreshed and to function well both mentally and physically.

The best way to judge if you’ve slept well is to look at how you feel the next day. If you feel exhausted, need a nap or are still feeling groggy a couple of hours after waking up, then chances are you aren’t sleeping properly.

While your husband may think he’s OK with just four to five hours of sleep, it may be worth pointing out the rise in the number of people getting less than six hours sleep is certainly a concern, with research suggesting that mental and physical problems become more pronounced in those sleeping for less than six hours.

The stats all point to the fact that those who frequently get fewer than six hours a night are at significantly increased risk of stroke and heart disease. Not sleeping enough may ramp up the “fight or flight” response to stress, releasing hormones that speed up heart rate and raise blood pressure. So lack of sleep can increase health risks.