You Can Close Your Eyes (For 7 Hours)

There is an advert on the TV which uses the song  'Lucky, Lucky, Lucky Me' to explain how the singer works eight hours, sleeps eight hours which leaves eight hours for fun and i have always assumed that eight hours of shut eye is some sort of scientific fact to allow our brains to do whatever brains do when we are sleeping, but turns out that the sweet spot is less than that.
A report by Sleep Specialists have narrowed it down to between 6 hours 24 minutes and 7 hours 48 minutes and anything more or less than that is linked to poorer brain, heart and immune health.
There is a gender factor because women need 15 to 20 minutes more sleep than men which i assume is due to ladies have bigger, more complex brains so we need those extra minutes and to be fair if length of sleep needed was due to how much brain there was to rearrange, i know some who could happily get by with a 10 minute nap but i'm no scientist so i may have made that bit up.   
The report does then go on to complicate things by saying that the actual correct amount of sleep varies depending on factors such as season, workload, stress, illness and safety but a rule of thumb is aim for about 7 hours sleep and you will be in the pink although the lyrics for that song may need to be rewritten because 8 hours kip is doing no favours to your brain, heart and immune system.