• Question: how much do you grow in your sleep?

    Asked by thanly on 28 Jun 2019.
    • Photo: Nina Rzechorzek

      Nina Rzechorzek answered on 28 Jun 2019:

      Great question – growth can happen during waking periods as well as sleep, and the vertebral column (spine) undergoes small amounts of compression during standing that are relieved when lying down (but this is not ‘true growth’ once the vertebral column has matured). However, rapid eye movement (REM) sleep in particular is really important for maturation of the brain. Proportionately, the amount of REM sleep we (and other mammals) get is highest just before birth when massive bursts of electrical activity during REM sleep promote brain cell growth and new connections between brain cells (neurons). There is a correlation between reduced amounts of REM sleep and autism – although whether this lack of REM is a cause, consequence, or an unrelated ‘bystander’ of the disorder remains to be proven. At 6 months of age there is roughly a 50/50 split between the amount of REM and non-REM sleep we experience in a night; by the late teen years it is more like 80/20 in favour of non-REM – the reason being that in adolescence lots of deep non-REM sleep is needed to ‘prune’ the brain connections we have made, removing useless connections and refining the circuits so that they become super-efficient. Although the amount of brain cell connectivity decreases overall during this brain development process, the physical size of our brain cells, and thus the physical size of the brain increases. In teenagers and young adults with schizophrenia there is a two-to-three-fold reduction in deep non-REM sleep, and it remains possible that this could be due to faulty ‘pruning’. Although most brain ‘growth’ has completed by the end of adolescence, some plasticity is retained in the system throughout adulthood – which is how we can form new memories and learn new things (although it gets harder!). Sleep is critical to consolidate these experiences and so I would argue that brain ‘growth’ continues during sleep throughout life.
      More generally, growth hormone normally surges at night, but this surge is shut down in people who are sleep deprived – so not getting enough sleep could certainly impact on your general growth whilst you are developing. Growth hormone is still important in adults too though, especially for replenishing the lining of blood vessels (the endothelium). This is one of the many reasons why sleep deprivation increases the risk of atherosclerosis, heart attack and stroke. Interesting point of note: at the turn of the millennium, there was an economic pressure in Greece to reduce the siestas (afternoon naps) typical of Greek culture – in a study of 23,000 adults followed over 6 years, those that stopped having siestas had a 37% increase in their risk of death from heart disease.
      Much of what I have discussed above is adapted from the book ‘Wy We Sleep’ by Matthew Walker – it’s based on a wealth of scientific evidence, beautifully written for a general audience, and covers all the latest things we know about the benefits of sleep and what happens to our bodies when we don’t get enough of it.